Previously, in Part I, Part II, Part III, Part IV and Part V of this series, we addressed these 7 concepts:

     #1 — What is cholesterol?

     #2 — What is the relationship between the cholesterol we eat and the cholesterol in our body?

     #3 — Is cholesterol bad?

     #4 – How does cholesterol move around our body?

     #5 – How do we measure cholesterol?

     #6 – How does cholesterol actually cause problems?

     #7 – Does the size of an LDL particle matter?

In this post we’ll continue to build out the story with the next concept:

     #8 – Why is it necessary to measure LDL-P, instead of just LDL-C?

(Not so) quick refresher on take-away points from previous posts, should you need it:

1. Cholesterol is “just” another fancy organic molecule in our body but with an interesting distinction: we eat it, we make it, we store it, and we excrete it – all in different amounts.
2. The pool of cholesterol in our body is essential for life.  No cholesterol = no life.
3. Cholesterol exists in 2 forms – unesterified or “free” (UC) and esterified (CE) – and the form determines if we can absorb it or not, or store it or not (among other things).
4. Much of the cholesterol we eat is in the form of CE. It is not absorbed and is excreted by our gut (i.e., leaves our body in stool). The reason this occurs is that CE not only has to be de-esterified, but it competes for absorption with the vastly larger amounts of UC supplied by the biliary route.
5. Re-absorption of the cholesterol we synthesize in our body (i.e., endogenous produced cholesterol) is the dominant source of the cholesterol in our body. That is, most of the cholesterol in our body was made by our body.
6. The process of regulating cholesterol is very complex and multifaceted with multiple layers of control.  I’ve only touched on the absorption side, but the synthesis side is also complex and highly regulated. You will discover that synthesis and absorption are very interrelated.
7. Eating cholesterol has very little impact on the cholesterol levels in your body. This is a fact, not my opinion.  Anyone who tells you different is, at best, ignorant of this topic.  At worst, they are a deliberate charlatan. Years ago the Canadian Guidelines removed the limitation of dietary cholesterol. The rest of the world, especially the United States, needs to catch up.  To see an important reference on this topic, please look here.
8. Cholesterol and triglycerides are not soluble in plasma (i.e., they can’t dissolve in water) and are therefore said to be hydrophobic.
9. To be carried anywhere in our body, say from your liver to your coronary artery, they need to be carried by a special protein-wrapped transport vessel called a lipoprotein.
10. As these “ships” called lipoproteins leave the liver they undergo a process of maturation where they shed much of their triglyceride “cargo” in the form of free fatty acid, and doing so makes them smaller and richer in cholesterol.
11. Special proteins, apoproteins, play an important role in moving lipoproteins around the body and facilitating their interactions with other cells.  The most important of these are the apoB class, residing on VLDL, IDL, and LDL particles, and the apoA-I class, residing for the most part on the HDL particles.
12. Cholesterol transport in plasma occurs in both directions, from the liver and small intestine towards the periphery and back to the liver and small intestine (the “gut”).
13. The major function of the apoB-containing particles is to traffic energy (triglycerides) to muscles and phospholipids to all cells. Their cholesterol is trafficked back to the liver. The apoA-I containing particles traffic cholesterol to steroidogenic tissues, adipocytes (a storage organ for cholesterol ester) and ultimately back to the liver, gut, or steroidogenic tissue.
14. All lipoproteins are part of the human lipid transportation system and work harmoniously together to efficiently traffic lipids. As you are probably starting to appreciate, the trafficking pattern is highly complex and the lipoproteins constantly exchange their core and surface lipids.
15. The measurement of cholesterol has undergone a dramatic evolution over the past 70 years with technology at the heart of the advance.
16. Currently, most people in the United States (and the world for that matter) undergo a “standard” lipid panel, which only directly measures TC, TG, and HDL-C.  LDL-C is measured or most often estimated.
17. More advanced cholesterol measuring tests do exist to directly measure LDL-C (though none are standardized), along with the cholesterol content of other lipoproteins (e.g., VLDL, IDL) or lipoprotein subparticles.
18. The most frequently used and guideline-recommended test that can count the number of LDL particles is either apolipoprotein B or LDL-P NMR, which is part of the NMR LipoProfile.  NMR can also measure the size of LDL and other lipoprotein particles, which is valuable for predicting insulin resistance in drug naïve patients, before changes are noted in glucose or insulin levels.
19. The progression from a completely normal artery to a “clogged” or atherosclerotic one follows a very clear path: an apoB containing particle gets past the endothelial layer into the subendothelial space, the particle and its cholesterol content is retained, immune cells arrive, an inflammatory response ensues “fixing” the apoB containing particles in place AND making more space for more of them.
20. While inflammation plays a key role in this process, it’s the penetration of the endothelium and retention within the endothelium that drive the process.
21. The most common apoB containing lipoprotein in this process is certainly the LDL particle. However, Lp(a) and apoB containing lipoproteins play a role also, especially in the insulin resistant person.
22. If you want to stop atherosclerosis, you must lower the LDL particle number. Period.
23. At first glance it would seem that patients with smaller LDL particles are at greater risk for atherosclerosis than patients with large LDL particles, all things equal.
24. “A particle is a particle is a particle.”  If you don’t know the number, you don’t know the risk.
25. To address this question, however, one must look at changes in cardiovascular events or direct markers of atherosclerosis (e.g., IMT) while holding LDL-P constant and then again holding LDL size constant.  Only when you do this can you see that the relationship between size and event vanishes.  The only thing that matters is the number of LDL particles – large, small, or mixed.

Concept #8 – Why is it necessary to measure LDL-P, instead of just LDL-C?

In the growing list of reasons why I used to refer to myself as “chick-repellant” in college, I have a confession to make: I find the topic of statistical concordance and discordance to be so exciting, I sometimes have a hard time containing myself. This may explain the paucity of girlfriends in college. Let me use an example to illustrate the distinction between these terms.  Let’s say you want to predict the change in home prices in the following year (I used to model this for a living).   There are at least a dozen parameters linked to this, including: GDP growth, unemployment, interest rates (both short term and long term, though to different degrees), housing inventory (i.e., how many houses are on the market), housing absorption (i.e., how quickly houses go from being on the market to being sold), major stock indices, and consumer confidence.  Historically, from the mid-1990’s until about the fourth quarter of 2006, this worked like clockwork.  While each of these variables had differing strengths of predicting changes in home prices, they all moved together.  For example, when GDP growth was robust, unemployment was low, interest rates were modest, housing inventories were about 60 to 90 days, etcetera.  All of these variables pointed to a predictable change in home values.

Around Q42006 (i.e., last 3 months of 2006), one of these variables began to deviate from the others.   The details aren’t important, but the point is one variable began to suggest home prices would fall while the others all pointed to a continued rise.   Prior to Q42006 these parameters were said to be concordant – they all predicted the same thing – either up or down.  By 2007, they became discordant – one variable said the sky was falling while others said everything was fine.

This was true on the “micro” level, too. [What I described above is called “macro” level.]  As a lender, it should be very important to know the risk of each and every loan you make (clearly this was part of the root problem in the age of mass securitization).  Will this person pay the loan back or will they default?

Same game here, but now a new set of even greater variables.  As a lender, if I want to know if YOU will default, I will want to know a lot of things about you, such as your agency credit risk scores, your bank account activity, payroll activity, how much you’re borrowing relative to the value of your house, where your house is located, and about 50 other things (literally).

Not surprisingly, the same thing that happened on the macro side happened on the micro side.  It became difficult to predict who would default and would not default because there were so many variables to consider and lenders didn’t know which ones were still predictive.  The models that predict default are very sensitive to the balance of these inputs.  When all of the variables are concordant, their accuracy is prophetic, as was the case from the mid-1990s until late 2006.  When some variables become discordant with each other, especially variables that were historically concordant with each other, really bad stuff happens, as became evident to me, personally, one Thursday afternoon in November 2007.  It became clear the sky was about to fall.  And, of course, it did.

What does real estate have to do with atherosclerosis?

Fortunately, predicting heart disease is a little easier than predicting changes in home prices.  It’s not perfect, of course, but it’s pretty good.  Why is it not perfect? For one thing, we can’t do the “perfect” experiment.  The “perfect” experiment would look something like this:

Take 100,000 people and randomize them into four matched groups, A, B, C, and D.  Wave a magic wand (you can see why this experiment hasn’t been and won’t be done) and give the folks in Group A an LDL particle concentration of, say, 700 nmol/L; those in Group B you give 1,200 nmol/L; those in Group C you give 1,600 nmol/L; and those in Group D get 2,000 nmol/L.

In our dream world, due to the randomization process, these four groups would be statistically identical in every way except one – they would, thanks to our magic wand, have a different number of LDL particles.  We would follow them without further intervention for 10 years and then compare their rates of heart disease, stroke, and death.

There are some areas in medicine where we can do such experiments.  But, we can’t do this experiment for this question.  Even when we do the next best thing — give people a drug that lowers their LDL-P and measure the impact of this intervention — there is always a chance we’ve done something in addition to “just” lowering LDL-P.   If you’ve been reading this series, you no doubt know my thoughts on this: while other factors are likely to be involved the pathogenesis of atherosclerosis (e.g., endothelial “health”, normal versus abnormal inflammatory response) the primary driver of atherosclerosis is the number of apoB trafficking lipoproteins in circulation, of which LDL particles are the vast majority.

The data below should further clarify this association.

What do concordant LDL-C and LDL-P values look like?

Among the two largest studies tracking the association between cholesterol and atherosclerotic mortality are the Framingham study and the MESA trial (the two largest trials were AMORIS and INTERHEART).  The figure below, which I’ve graciously borrowed from Jim Otvos, shows the risk stratification of LDL-C (top) and LDL-P (bottom) from the Framingham study and MESA trial, respectively. As you can see, conveniently, LDL-C values in mg/dL are about 10x off from LDL-P values in nmol/L.   In other words, in the Framingham population, the 20^th percentile value of LDL-C was 100 mg/dL, while the MESA trial found the 20^th percentile of the population to have an LDL-P concentration of 1,000 nmol/L.  As you will see by the end of this post, this “rule of the thumb” should never be used to infer LDL-P from LDL-C.

If this were always the case – that is, if LDL-C and LDL-P were always concordant – we could conclude that LDL-C and LDL-P would be of equal value in predicting heart disease.  Obviously this is not the case, or I wouldn’t be making such a fuss over the distinction.  But how bad is it?

What do discordant LDL-C and LDL-P values look like?

The figure below, from the Journal of Clinical Lipidology, shows the cumulative incidence of cardiovascular events (e.g., myocardial infarction, death) over time in three sub-populations:

1. Those with concordant LDL-P and LDL-C (black line);
2. Those with discordant LDL-P and LDL-C (LDL-P>LDL-C, shown by the red line);
3. Those with discordant LDL-P and LDL-C (LDL-P<LDL-C, shown by the blue line).

This analysis was done using a Cox proportional hazard model and was adjusted for age, sex, and race.  The steeper the line the more people in that sub-population died or experienced adverse cardiac events relative to other sub-populations.  In other words, the folks in the red group had the worst outcomes, followed by the folks in the black group, followed by the folks in the blue group.

What can we infer from these data?

First, we confirm what I alluded to above.  Namely, that a non-zero percent of the population do not have LDL-C and LDL-P values that predict the same level of risk.  However, and perhaps more importantly, we get another look at an important theme of this series: LDL-P is driving atherosclerotic risk, not LDL-C.   If LDL-P and LDL-C were equally “bad” – even when discordant – you would expect the blue line to be as steep as the red line (and both to be steeper than the black line). But this is not the case.

Let’s look at these data parsed out another way.  Below we see the four possible subgroups, from the top:

1. Not low LDL-P, low LDL-C (red line);
2. Not low LDL-P, not low LDL-C (yellow line);
3. Low LDL-P, low LDL-C (black line); and
4. Low LDL-P, not low LDL-C (blue line).

Note that “low” is defined below the 30^th percentile and “not low” is defined as greater than 30^th percentile for each variable.   This figure is even more revealing than the one above.  Again, it demonstrates the frequency of discordance (about 20% in this population with these cut-off points), and it shows the importance of LDL-P’s predictive power, relative to that of LDL-C.

In fact, though not statistically significant, the highest risk group has high LDL-P and actually has low LDL-C (I’ll give you a hint of why, below) while the lowest risk group has low LDL-P and not-low LDL-C.  *This is not a typo.

The highest risk and lowest risk groups are those with discordant LDL-C and LDL-P.  The high risk group has high LDL-P and low LDL-C, while the lowest risk group has high LDL-C with low LDL-P. Only a minority of physicians would know that there is a segment of the population with elevated LDL-C who are at low risk! The same conclusion will be drawn from the next study.

Let’s look at an even longer-term follow up study, below.  This study followed a Framingham offspring cohort of about 2,500 patients over a median time period of almost 15 years in each of the four possible groups (i.e., high-high, high-low, low-high, and low-low) and tracked event-free survival.  In this analysis the cut-off points for LDL-P and LDL-C were the median population values of 1,414 nmol/L and131 mg/dL, respectively. So “high” implies above these values; “low” implies below these values.  Kaplan-Meier survival curves are displayed over a 16 year period – the steeper the slope of the line the worse the outcome (survival).

The same patterns are observed:

1. LDL-P is the best predictor of adverse cardiac events.
2. LDL-C is only a good predictor of adverse cardiac events when it is concordant with LDL-P; otherwise it is a poor predictor of risk.

Amazingly the persons with the worst survival had low (below median) LDL-C but high LDL-P.  The patients most likely to have high LDL-P with unremarkable or low LDL-C are those with either small LDL particles, or TG-rich / cholesterol poor LDL particles, or both (e.g., insulin resistant patients, metabolic syndrome patients, T2DM patients).   This explains why small LDL particles, while no more atherogenic on a per particle basis than large particles, are a marker for something sinister.

Populations where LDL-P and LDL-C discordance are even more prevalent

As I described above, the discordance between LDL-P and LDL-C is exacerbated in patients with metabolic syndrome.   The figure below, MESA data, again borrowed from Jim Otvos, presents this difference in an elegant way.  The horizontal axes show LDL-P concentration in the usual units, nmol/L.

Patients with LDL-C between 100 and 118 mg/dL (i.e., second quartile of risk: 25^th to 50^th percentile) are shown without metabolic syndrome (top) and with metabolic syndrome (bottom).  In the patients without metabolic syndrome, LDL-C under-predicts cardiac risk 22% of the time, consistent with the population data I have shown you earlier.  However, when you look at the patients with metabolic syndrome, you can see that 63% of the time their risk of cardiac disease is under-predicted.  Again, not a typo.

There are so many subsets and cut-off points that I could devote ten more posts to showing you every one of these analyses.  Let me finish this point with the most recent, hot-off-the-press (actually, still in press in the American Journal of Cardiology, though you can get a preprint here) analysis of which Tom Dayspring is one of the authors.

These data were collected from nearly 2,000 patients with diabetes who presented with “perfect” standard cholesterol numbers: LDL-C < 70 mg/dL; HDL-C > 40 mg/dL; TG <150 mg/dL.  However, only in 22% of cases were their LDL-P concordant with LDL-C.  That is, in only 22% of cases did these patients have an LDL-P level below 700 nmol/L.

Remember, LDL-C < 70 mg/dL is considered VERY low risk – the 5^th percentile.  Yet, by LDL-P, the real marker of risk, 35% of these patients had more than 1,000 nmol/L and 7% were high risk.  When you do this analysis with the same group of patients stratified by less stringent LDL-C criteria (e.g., <100 mg/dL) the number of patients in the high risk group is even higher.

The real world tragedy: 90-95% of physicians, including cardiologists, would bet their own lives that persons with an LDL-C < 70 mg/dL have no atherosclerotic risk. 

Tim Russert, shortly before his death, had his LDL-C level checked.  It was less than 70 mg/dL.  Sadly, his doctors didn’t realize they should also have been checking his LDL-P or apoB.  The figure below, which is from one of Tom Dayspring’s presentations, shows data from this study of nearly 137,000 patients hospitalized for coronary artery disease between 2000 and 2006.  As you can see, LDL-C fails to even reasonably predict cardiovascular disease in a patient population sick enough to show up in the hospital with chest pain or outright myocardial infarction.

Why are LDL-C and LDL-P so often discordant?

Think back to what you learned in a previous post in this series.  LDL particles traffic not only cholesterol ester but also triglycerides.  Each and every LDL particle has a variable number of cholesterol molecules which, because of constant particle remodeling, is constantly changing.  In other words, of the several quadrillion LDL particles floating in your plasma, no two are carrying the exact same number of cholesterol molecules. It takes many more cholesterol-depleted LDL particles than cholesterol-rich LDL particles to traffic a given cholesterol mass (i.e., number of cholesterol molecules) per volume of plasma (i.e., per dL).  Core cholesterol mass is related to both LDL particle size (the volume of a sphere is a third power of the radius — it can take 40-70% more small particles than large LDL particles to traffic a given cholesterol mass) and the number of TG molecules per LDL particle.

TG molecules are larger than cholesterol ester molecules, so as the number of TG molecules per particle increases, the number of cholesterol molecules will be less – in a very non-linear manner. Regardless of size it takes many more TG-rich LDL particles (which are necessarily cholesterol-depleted) to traffic a given cholesterol mass than TG-poor LDL particles.  The persons with the highest LDL particles typically (though not always) have small LDL particles that are TG-rich.  These are incredibly cholesterol-depleted LDL particles.

Summary

Take a look at this figure below from the 2011 Otvos et al. paper I referenced above.  It’s a scatterplot of each data point (i.e., patient) in the study. The solid red line shows perfect concordance between LDL-P and LDL-C.  The dashed red lines show a +/- 12% margin on each side.  Look at how many dots (remember: each dot represents a person) lie OUTSIDE of the dashed red lines. Now look again.

When people argue with me about why it’s unnecessary to check LDL-P or apoB because it’s much easier and cheaper to check LDL-C, I like to remind them of what Clint Eastwood would probably say in such a situation:  “You’ve got to ask yourself one question: Do I feel lucky? Well, do ya, punk?”

1. With respect to laboratory medicine, two markers that have a high correlation with a given outcome are concordant – they equally predict the same outcome. However, when the two tests do not correlate with each other they are said to be discordant.
2. LDL-P (or apoB) is the best predictor of adverse cardiac events, which has been documented repeatedly in every major cardiovascular risk study.
3. LDL-C is only a good predictor of adverse cardiac events when it is concordant with LDL-P; otherwise it is a poor predictor of risk.
4. There is no way of determining which individual patient may have discordant LDL-C and LDL-P without measuring both markers.
5. Discordance between LDL-C and LDL-P is even greater in populations with metabolic syndrome, including patients with diabetes.  Given the ubiquity of these conditions in the U.S. population, and the special risk such patients carry for cardiovascular disease, it is difficult to justify use of LDL-C, HDL-C, and TG alone for risk stratification in all but the most select patients.
6. This begs the question: if indeed LDL-P is always as good and in most cases better than LDL-C at predicting cardiovascular risk, why do we continue to measure (or calculate) LDL-C at all?

In Part I, Part II, Part III and Part IV of this series, we addressed these 6 concepts:

     #1 — What is cholesterol?

     #2 — What is the relationship between the cholesterol we eat and the cholesterol in our body?

     #3 — Is cholesterol bad?

     #4 – How does cholesterol move around our body?

     #5 – How do we measure cholesterol?

     #6 – How does cholesterol actually cause problems?

In this post we’ll continue to build out the story with the next concept:

     #7 – Does the size of an LDL particle matter?

Quick refresher on take-away points from previous posts, should you need it:

1. Cholesterol is “just” another fancy organic molecule in our body but with an interesting distinction: we eat it, we make it, we store it, and we excrete it – all in different amounts.
2. The pool of cholesterol in our body is essential for life.  No cholesterol = no life.
3. Cholesterol exists in 2 forms – unesterified or “free” (UC) and esterified (CE) – and the form determines if we can absorb it or not, or store it or not (among other things).
4. Much of the cholesterol we eat is in the form of CE. It is not absorbed and is excreted by our gut (i.e., leaves our body in stool). The reason this occurs is that CE not only has to be de-esterified, but it competes for absorption with the vastly larger amounts of UC supplied by the biliary route.
5. Re-absorption of the cholesterol we synthesize in our body (i.e., endogenous produced cholesterol) is the dominant source of the cholesterol in our body. That is, most of the cholesterol in our body was made by our body.
6. The process of regulating cholesterol is very complex and multifaceted with multiple layers of control.  I’ve only touched on the absorption side, but the synthesis side is also complex and highly regulated. You will discover that synthesis and absorption are very interrelated.
7. Eating cholesterol has very little impact on the cholesterol levels in your body. This is a fact, not my opinion.  Anyone who tells you different is, at best, ignorant of this topic.  At worst, they are a deliberate charlatan. Years ago the Canadian Guidelines removed the limitation of dietary cholesterol. The rest of the world, especially the United States, needs to catch up.  To see an important reference on this topic, please look here.
8. Cholesterol and triglycerides are not soluble in plasma (i.e., they can’t dissolve in water) and are therefore said to be hydrophobic.
9. To be carried anywhere in our body, say from your liver to your coronary artery, they need to be carried by a special protein-wrapped transport vessel called a lipoprotein.
10. As these “ships” called lipoproteins leave the liver they undergo a process of maturation where they shed much of their triglyceride “cargo” in the form of free fatty acid, and doing so makes them smaller and richer in cholesterol.
11. Special proteins, apoproteins, play an important role in moving lipoproteins around the body and facilitating their interactions with other cells.  The most important of these are the apoB class, residing on VLDL, IDL, and LDL particles, and the apoA-I class, residing for the most part on the HDL particles.
12. Cholesterol transport in plasma occurs in both directions, from the liver and small intestine towards the periphery and back to the liver and small intestine (the “gut”).
13. The major function of the apoB-containing particles is to traffic energy (triglycerides) to muscles and phospholipids to all cells. Their cholesterol is trafficked back to the liver. The apoA-I containing particles traffic cholesterol to steroidogenic tissues, adipocytes (a storage organ for cholesterol ester) and ultimately back to the liver, gut, or steroidogenic tissue.
14. All lipoproteins are part of the human lipid transportation system and work harmoniously together to efficiently traffic lipids. As you are probably starting to appreciate, the trafficking pattern is highly complex and the lipoproteins constantly exchange their core and surface lipids.
15. The measurement of cholesterol has undergone a dramatic evolution over the past 70 years with technology at the heart of the advance.
16. Currently, most people in the United States (and the world for that matter) undergo a “standard” lipid panel, which only directly measures TC, TG, and HDL-C.  LDL-C is measured or most often estimated.
17. More advanced cholesterol measuring tests do exist to directly measure LDL-C (though none are standardized), along with the cholesterol content of other lipoproteins (e.g., VLDL, IDL) or lipoprotein subparticles.
18. The most frequently used and guideline-recommended test that can count the number of LDL particles is either apolipoprotein B or LDL-P NMR, which is part of the NMR LipoProfile.  NMR can also measure the size of LDL and other lipoprotein particles, which is valuable for predicting insulin resistance in drug naïve patients, before changes are noted in glucose or insulin levels.
19. The progression from a completely normal artery to a “clogged” or atherosclerotic one follows a very clear path: an apoB containing particle gets past the endothelial layer into the subendothelial space, the particle and its cholesterol content is retained, immune cells arrive, an inflammatory response ensues “fixing” the apoB containing particles in place AND making more space for more of them.
20. While inflammation plays a key role in this process, it’s the penetration of the endothelium and retention within the endothelium that drive the process.
21. The most common apoB containing lipoprotein in this process is certainly the LDL particle. However, Lp(a) and apoB containing lipoproteins play a role also, especially in the insulin resistant person.
22. If you want to stop atherosclerosis, you must lower the LDL particle number. Period.

Concept #7 – Does the size of an LDL particle matter?

There are few, if any, topics in lipidology that generate more confusion and argument that this one.  I’ve been leading up to it all month, so I think the time is here to address this issue head on.  I’ve read many papers and seen many lectures on this topic, but the one that stole my heart was a lecture given by Jim Otvos at the ADA 66^th Scientific Sessions in Washington, DC.   Some of the figures I am using in this post are taken directly or modified from his talk or subsequent discussions.

At the outset of this discussion I want to point out two clinical scenarios to keep in mind:

1. The most lethal lipoprotein disorder is familial hypercholesterolemia, which I have discussed in previous posts.  Such patients all have large LDL particles, but most of these patients die in childhood or early adulthood if not treated with medications to reduce particle number.
2. Conversely, diabetic patients and other patients with advanced metabolic syndrome have small LDL particles, yet often live well into their 50s and 60s before succumbing to atherosclerotic diseases.

The common denominator is that both sets of patients in (1) and (2) have high LDL-P.  What I’m going to attempt to show you today is that once adjusted for particle number, particle size has no statistically significant relationship to cardiovascular risk.  But first, some geometry.

“Pattern A” versus “Pattern B” LDL

The introduction of gradient gel electrophoresis about 30 years ago is what really got people interested in the size of LDL particles.  There is no shortage of studies of the past 25 years demonstrating that of the following 2 scenarios, one has higher risk, all other things equal.  [This is a big disclaimer and I went back and forth for a while before deciding to include this point.  It is an uncharacteristic oversimplification. If you’ve been reading this blog for a while, you’ll know I’m rarely accused of that sin – but I’m about to be].

Here’s the example: Consider 2 patients, both with the same total content of cholesterol in their LDL particles, say, 130 mg/dL.  Furthermore, assume each has the “ideal” ratio of core cholesterol ester-to-triglyceride (recall from Part I and III of this series, this ratio is 4:1).  I’m going to explain in a subsequent post why this assumption is probably wrong as often as it’s right, but for the purpose of simplicity I want to make a geometric point.

1. LDL-C = 130 mg/dL, Pattern A (large particles) – person on the left in the figure below
2. LDL-C = 130 mg/dL, Pattern B (small particles) – person on the right in the figure below

Under the set of assumptions I’ve laid out, case #2 is the higher risk case.  In other words, at the same concentration of cholesterol within LDL particles, assuming the same ratio of CE:TG, it is mathematically necessary the person on the right, case #2, has more particles, and therefore has greater risk.

Bonus concept: What one really must know is how many cholesterol molecules there are per LDL particle.  It always requires more cholesterol-depleted LDL particles than cholesterol-rich LDL particles to traffic cholesterol in plasma, and the number of cholesterol molecules depends on both size and core TG content.  The more TG in the particle, the less the cholesterol in the particle.

So why does the person on the right have greater risk?  Is it because they have more particles?  Or is it because they have smaller particles?

This is the jugular question I want to address today.

If you understand that the person on the right, under the very careful and admittedly overly simplified assumptions I’ve given, is at higher risk than the person on the left, there are only 4 possible reasons:

1. Small LDL particles are more atherogenic than large ones, independent of number.
2. The number of particles is what increases atherogenic risk, independent of size.
3. Both size and number matter, and so the person on the right is “doubly” at risk.
4. Neither feature matters and these attributes (i.e., size and number) are markers for something else that does matter.

Anyone who knows me well knows I love to think in MECE terms whenever possible.  This is a good place to do so.

I’m going to rule out Reason #4 right now because if I have not yet convinced you that LDL particles are the causative agent for atherosclerosis, nothing else I say matters.  The trial data are unimpeachable and there are now 7 guidelines around the world advocating particle number measurement for risk assessment. The more LDL particles you have, the greater your risk of atherosclerosis.

But how do we know if Reason #1, #2, or #3 is correct?

This figure (one of the most famous in this debate) is from the Quebec Cardiovascular Study, published in 1997, in Circulation.  You can find this study here.

This is kind of a complex graph if you’re not used to looking at these.  It shows relative risk – but in 2 dimensions.  It’s looking at the role of LDL size and apoB (a proxy for LDL-P, you’ll recall from previous posts).  What seems clear is that in patients with low LDL-P (i.e., apoB < 120 mg/dl), size does not matter.  The relative risk is 1.0 in both cases, regardless of peak LDL size.  However, in patients with lots of LDL particles (i.e., apoB > 120 mg/dl), smaller peak LDL size seems to carry a much greater risk – 6.2X.

If you just looked at this figure, you might end up drawing the conclusion that both size and number are independently predictive of risk (i.e., Reason #3, above).  Not an illogical conclusion…

What is not often mentioned, however, is what is in the text of the article:

“Among lipid, lipoprotein,and apolipoprotein variables, apo B [LDL-P] came out as the best and only significant predictor of ischemic heart disease (IHD) risk in multivariate stepwiselogistic analyses (P=.002).”

“LDL-PPD [peak LDL particle diameter] — as a continuous variable did not contribute to the risk of IHD after the contribution of apo B levels to IHD risk had been considered.”

What’s a continuous variable?  Something like height or weight, where the possible values are infinite between a range.  Contrast this with discrete variables like “tall” or “short,” where there are only two categories. For example, if I define “tall” as greater than 6 feet, the entire population of the world could be placed in two buckets: Those who are “short” (i.e., less than 6 feet tall) and those who are “tall” (i.e., those who are 6 feet tall and taller). This figure shows LDL size like it’s a discrete variable – “large” or “small” – but obviously it is not. It’s continuous, meaning it can take on any value, not just “large” or “small.”  When this same analysis is done using LDL size as the continuous variable it is, the influence of size goes away and only apoB (i.e., LDL-P) matters.

This effect has been observed subsequently, including the famous Multi-Ethnic Study of Atherosclerosis (MESA) trial, which you can read here.  The MESA trial looked at the association between LDL-P, LDL-C, LDL size, IMT (intima-media thickness – the best non-invasive marker we have for atherosclerosis), and many other parameters in about 5,500 men and women over a several year period.

This study used the same sort of statistical analysis as the study above to parse out the real role of LDL-P versus particle size, as summarized in the table below.

This table shows us that when LDL-P is NOT taken into account (i.e., “unadjusted” analysis), an increase of one standard deviation in particle size is associated with 20.9 microns of LESS atherosclerosis, what one might expect if one believes particle size matters.  Bigger particles, less atherosclerosis.

However, and this is the important part, when the authors adjusted for the number of LDL particles (in yellow), the same phenomenon was not observed.  Now an increase in LDL particle size by 1 standard deviation was associated with an ADDITIONAL 14.5 microns of atherosclerosis, albeit of barely any significance (p=0.05).

Let me repeat this point: Once you account for LDL-P, the relationship of atherosclerosis to particle size is abolished (and even trends towards moving in the “wrong” direction – i.e., bigger particles, more atherosclerosis).

Let me use another analysis to illustrate this point again.  If you adjust for age and sex, but not LDL-P [left graph, below], changes in the number of LDL particles (shown in quintiles, so each group shows changes by 20% fractions) seem to have no relationship with IMT (i.e., atherosclerosis).

However, when you adjust for small LDL-P [right graph, below], it becomes clear that increased numbers of large LDL particles significantly increase risk.

I’ve only covered a small amount of the work addressing this question, but this issue is now quite clear.  A small LDL particle is no more atherogenic than a large one, but only by removing confounding factors is this clear.   So, if you look back at the figure I used to address this question, it should now be clear that Reason #2 is the correct one.

This does not imply that the “average” person walking around with small particles is not at risk.  It only implies the following:

1. The small size of their particles is probably a marker for something else (e.g., metabolic derangement due to higher trafficking of triglycerides within LDL particles);
2. Unless you know their particle number (i.e., LDL-P or apoB), you actually don’t know their risk.

Let’s wrap it up here for this week.  Next week we’ll address another question that’s probably been on your mind: Why do we need to measure LDL-P or apoB?  Isn’t the LDL-C test my doctor orders enough to predict my risk?

Summary

• At first glance it would seem that patients with smaller LDL particles are at greater risk for atherosclerosis than patients with large LDL particles, all things equal.  Hence, this idea that Pattern A is “good” and Pattern “B” is bad has become quite popular.
• To address this question, however, one must look at changes in cardiovascular events or direct markers of atherosclerosis (e.g., IMT) while holding LDL-P constant and then again holding LDL size constant.  Only when you do this can you see that the relationship between size and event vanishes.  The only thing that matters is the number of LDL particles – large, small, or mixed.
• “A particle is a particle is a particle.”  If you don’t know the number, you don’t know the risk.

(To Part VI »)

Previously, in Part I, Part II and Part III of this series, we addressed these 5 concepts:

     #1 — What is cholesterol?

     #2 — What is the relationship between the cholesterol we eat and the cholesterol in our body?

     #3 — Is cholesterol bad?

     #4 – How does cholesterol move around our body?

     #5 – How do we measure cholesterol?

In this post we’ll continue to build out the story with the next concept:

     #6 – How does cholesterol actually cause problems?

Asked another way, how does someone end up with a coronary artery that looks like the one in the picture above?

Quick refresher on take-away points from previous posts, should you need it:

1. Cholesterol is “just” another fancy organic molecule in our body but with an interesting distinction: we eat it, we make it, we store it, and we excrete it – all in different amounts.
2. The pool of cholesterol in our body is essential for life.  No cholesterol = no life.
3. Cholesterol exists in 2 forms – unesterified or “free” (UC) and esterified (CE) – and the form determines if we can absorb it or not, or store it or not (among other things).
4. Much of the cholesterol we eat is in the form of CE. It is not absorbed and is excreted by our gut (i.e., leaves our body in stool). The reason this occurs is that CE not only has to be de-esterified, but it competes for absorption with the vastly larger amounts of UC supplied by the biliary route.
5. Re-absorption of the cholesterol we synthesize in our body (i.e., endogenous produced cholesterol) is the dominant source of the cholesterol in our body. That is, most of the cholesterol in our body was made by our body.
6. The process of regulating cholesterol is very complex and multifaceted with multiple layers of control.  I’ve only touched on the absorption side, but the synthesis side is also complex and highly regulated. You will discover that synthesis and absorption are very interrelated.
7. Eating cholesterol has very little impact on the cholesterol levels in your body. This is a fact, not my opinion.  Anyone who tells you different is, at best, ignorant of this topic.  At worst, they are a deliberate charlatan. Years ago the Canadian Guidelines removed the limitation of dietary cholesterol. The rest of the world, especially the United States, needs to catch up.  To see an important reference on this topic, please look here.
8. Cholesterol and triglycerides are not soluble in plasma (i.e., they can’t dissolve in water) and are therefore said to be hydrophobic.
9. To be carried anywhere in our body, say from your liver to your coronary artery, they need to be carried by a special protein-wrapped transport vessel called a lipoprotein.
10. As these “ships” called lipoproteins leave the liver they undergo a process of maturation where they shed much of their triglyceride “cargo” in the form of free fatty acid, and doing so makes them smaller and richer in cholesterol.
11. Special proteins, apoproteins, play an important role in moving lipoproteins around the body and facilitating their interactions with other cells.  The most important of these are the apoB class, residing on VLDL, IDL, and LDL particles, and the apoA-I class, residing for the most part on the HDL particles.
12. Cholesterol transport in plasma occurs in both directions, from the liver and small intestine towards the periphery and back to the liver and small intestine (the “gut”).
13. The major function of the apoB-containing particles is to traffic energy (triglycerides) to muscles and phospholipids to all cells. Their cholesterol is trafficked back to the liver. The apoA-I containing particles traffic cholesterol to steroidogenic tissues, adipocytes (a storage organ for cholesterol ester) and ultimately back to the liver, gut, or steroidogenic tissue.
14. All lipoproteins are part of the human lipid transportation system and work harmoniously together to efficiently traffic lipids. As you are probably starting to appreciate, the trafficking pattern is highly complex and the lipoproteins constantly exchange their core and surface lipids.
15. The measurement of cholesterol has undergone a dramatic evolution over the past 70 years with technology at the heart of the advance.
16. Currently, most people in the United States (and the world for that matter) undergo a “standard” lipid panel which only directly measures TC, TG, and HDL-C.  LDL-C is measured or most often estimated.
17. More advanced cholesterol measuring tests do exist to directly measure LDL-C (though none are standardized), along with the cholesterol content of other lipoproteins (e.g., VLDL, IDL) or lipoprotein subparticles.
18. The most frequently used and guideline-recommended test that can count the number of LDL particles is either apolipoprotein B or LDL-P NMR which is part of the NMR LipoProfile.  NMR can also measure the size of LDL and other lipoprotein particles, which is valuable for predicting insulin resistance in drug naïve patients (i.e., those patients not on cholesterol-lowering drugs), before changes are noted in glucose or insulin levels.

Concept #6 – How does cholesterol actually cause problems?

If you remember only one factoid from the previous three posts on this topic, remember this: If you were only “allowed” to know one metric to understand your risk of heart disease it would be the number of apoB particles (90-95% of which are LDLs) in your plasma.  In practicality, there are two ways to do this:

1. Directly measure (i.e., not estimate) the concentration of apoB in your plasma (several technologies and companies offer such an assay). Recall, there is one apoB molecule per particle;
2. Directly measure the number of LDL particles in your plasma using NMR technology.

If this number is high, you are at risk of atherosclerosis.  Everything else is secondary.

Does having lots of HDL particles help?  Probably, especially if they are “functional” at carrying out reverse cholesterol transport, but it’s not clear if it matters when LDL particle count is low. In fact, while many drugs are known to increase the cholesterol content of HDL particles (i.e., HDL-C), not one to date has ever shown a benefit from doing so.  Does having normal serum triglyceride levels matter? Probably, with “normal” being defined as < 70-100 mg/dL, though it’s not entirely clear this is an independent predictor of low risk. Does having a low level of LDL-C matter?  Not if LDL-P (or apoB) are high, or better said, not when the two markers are discordant.

But why?

As with the previous topics in this series, this question is sufficiently complex to justify several textbooks – and it’s still not completely understood.  My challenge, of course, is to convey the most important points in a fraction of that space and complexity.

Let’s focus, specifically, on the unfortunately-ubiquitous clinical condition of atherosclerosis – the accumulation of sterols and inflammatory cells within an artery wall which may (or may not) narrow the lumen of the artery.

Bonus concept: It’s important to keep in mind that this disease process is actually within the artery wall and it may or may not affect the arterial lumen, which is why angiograms can be normal in persons with advanced atherosclerosis.  As plaque progresses it can encroach into the lumen leading to ischemia (i.e., lack of oxygen delivery to tissues) as the narrowing approaches 70-75%, or the plaque can rupture leading to a thrombosis: partial leading to ischemia or total leading to infarction (i.e., tissue death).

To be clear, statistically speaking, this condition (atherosclerotic induced ischemia or infarction) is the most common one that will result in the loss of your life.  For most of us, atherosclerosis (most commonly within coronary arteries, but also carotid or cerebral arteries) is the leading cause of death, even ahead of all forms of cancer combined.    Hence, it’s worth really understanding this problem.

In this week’s post I am going to focus exclusively on what I like to call the “jugular issue” – that is, I’m going to discuss the actual mechanism of atherosclerosis.   I’m not going to discuss treatment (yet).  We can’t get into treatment until we really understand the cause.

“It is in vain to speak of cures, or think of remedies, until such time as we have considered of the causes . . . cures must be imperfect, lame, and to no purpose, wherein the causes have not first been searched.”

–Robert Burton, The Anatomy of Melancholy, 1893

The sine qua non of atherosclerosis is the presence of sterols in arterial wall macrophages.  Sterols are delivered to the arterial wall by the penetration of the endothelium by an apoB-containing lipoprotein, which transport the sterols.  In other words, unless an apoB-containing lipoprotein particle violates the border created by an endothelium cell and the layer it protects, the media layer, there is no way atherogenesis occurs. 

For now, let’s focus only on the most ubiquitous apoB-containing lipoprotein, the LDL particle. Yes, other lipoproteins also contain apoB (e.g., chylomicrons, remnant lipoproteins such as VLDL remnants, IDL and Lp(a)), but they are few in number relative to LDL particles.  I will address them later.

The endothelium is the one-cell-thick-layer which lines the lumen (i.e., the “tube”) of a vessel, in this case, the artery.  Since blood is in direct contact with this cell all the time, all lipoproteins – including LDL particles – come in constant contact with such cells.

So what drives an LDL particle to do something as sinister as to leave the waterway (i.e., the bloodstream) and “illegally” try to park at a dock (i.e., behind an endothelial cell)?  Well, it is a gradient driven process which is why particle number is the key driving parameter.

As it turns out, this is probably a slightly less important question than the next one: what causes the LDL particle to stay there?  In the parlance of our metaphor, not only do we want to know why the ship leaves the waterway to illegally park in the dock, but why does it stay parked there?  This phenomenon is called “retention.”

Finally, if there was some way an LDL particle could violate the endothelium, AND be retained in the space behind the cell (away from the lumen on the side aptly called the sub-endothelial side) BUT not elicit an inflammatory (i.e., immune) response, would it matter?

I don’t know.  But it seems that not long after an LDL particle gets into the sub-endothelial space and takes up “illegal” residence (i.e., binds to arterial wall proteoglycans), it is subject to oxidative forces and as one would expect an inflammatory response is initiated.  The result is full blown mayhem.  Immunologic gang warfare breaks out and cells called monocytes and macrophages and mast cells show up to investigate.  When they arrive, and find the LDL particle, they do all they can to remove it.  In some cases, when there are few LDL particles, the normal immune response is successful.  But, it’s a numbers game.  When LDL particle invasion becomes incessant, even if the immune cells can remove some of them, it becomes a losing proposition and the actual immune response to the initial problem becomes chronic and maladaptive and expands into the space between the endothelium and the media.

The multiple-sterol-laden macrophages or foam cells coalesce, recruit smooth muscle cells, induce microvascularization, and before you know it complex, inflamed plaque occurs. Microhemorrhages and microthrombus formations occur within the plaque. Ultimately the growing plaque invades the arterial lumen or ruptures into the lumen inducing luminal thrombosis. Direct luminal encroachment by plaque expansion or thrombus formation causes the lumen of the artery to narrow, which may or may not cause ischemia.

Before we go any further, take a look at the figure below from an excellent review article on this topic from the journal Circulation – Subendothelial Lipoprotein Retention as the Initiative Process in Atherosclerosis.  This figure also discuss treatment strategies, but for now just focus on the pathogenesis (i.e., the cause of the problem).

In this figure you can see the progression:

1. LDL particles (and a few other particles containing apoB) enter the sub-endothelium
2. Some of these particles are retained, especially in areas where there is already a bit of extra space for them (called pre-lesion susceptible areas)
3. “Early” immune cells initiate an inflammatory response which includes the direct interaction between the LDL particle and proteins called proteoglycans.
4. The proteoglycans further shift the balance of LDL particle movement towards retention.  Think of them as “cement” keeping the LDL particles and their cholesterol content in the sub-endothelial space.
5. More and more apoB containing particles (i.e., LDL particles and the few other particles containing apoB) enter the sub-endothelial space and continue to be retained, due to the existing “room” being created by the immune response.
6. As this process continues, an even more advanced form of immune response – mediated by cells called T-cells – leads to further retention and destruction of the artery wall.
7. Eventually, not only does the lumen of the artery narrow, but a fibrous cap develops and plaques take form.
8. It is most often these plaques that lead to myocardial infarction, or heart attacks, as they eventually dislodge and acutely obstruct blood flow to the portion of muscle supplied by the artery.

Another way to see this progression is shown in the figure below, which shows the histologic progression of atherosclerosis in the right coronary artery from human autopsy specimens.  This figure is actually a bit confusing until you understand what you’re looking at.  Each set of 3 pictures shows the same sample, but with a different kind of histological stain.  Each row represents a different specimen.

• The column on the left uses a stain to highlight the distinction between the intimal and media layer of the artery call.  The intima, recall, is the layer just below the endothelium and should not be as thick as shown here.
• The middle column uses a special stain to highlight the presence of lipids within the intimal layer.
• The right column uses yet a different stain to highlight the presence of macrophages in the intima and the media.  Recall, macrophages are immune cells that play an important role of the inflammatory cascade leading to atherosclerosis.

What is particularly compelling about this sequence of figures is that you can see the trigger of events from what is called diffuse intimal thickening (“DIT”), which exacerbates the retention of lipoproteins and their lipid cargo, only then to be followed by the arrival of immune cells, which ultimately lead the inflammatory changes responsible for atherosclerosis.

Why LDL-P matters most

You may be asking the chicken and egg question:

Which is the cause – the apoB containing LDL particle OR the immune cells that “overreact” to them and their lipid cargo?

You certainly wouldn’t be alone in asking this question, as many folks have debated this exact question for years.  The reason, of course, it is so important to ask this question is captured by the Robert Burton quote, above.  If you don’t know the cause, how can you treat the disease?

Empirically, we know that the most successful pharmacologic interventions demonstrated to reduce coronary artery disease are those that reduce LDL-P and thus delivery of sterols to the artery. (Of course, they do other things also, like lower LDL-C, and maybe even reduce inflammation.)

Perhaps more compelling is the “natural experiment” of people with genetic alterations leading to elevated or reduced LDL-P.  Let’s consider an example of each:

1. Cohen, et al. reported in the New England Journal of Medicine in 2006 on the cases of patients with mutations in an enzyme called proprotein convertase subtilisin type 9 or PCSK9 (try saying that 10 times fast).   Normally, this proteolytic enzyme degrades LDL receptors on the liver.  Patients with mutations (“nonsense mutations” to be technically correct, meaning the enzyme is somewhat less active) have less destruction of hepatic LDL receptors.  Hence, they have more sustained expression of hepatic LDL receptors, improved LDL clearance from plasma and therefore fewer LDL particles.  These patients have very low LDL-P and LDL-C concentrations (5-40 mg/dL) and very low incidence of heart disease.  Note that a reduction in PCSK9 activity plays no role in reducing inflammation.
2. Conversely, patients with familial hypercholesterolemia (known as FH) have the opposite problem.  While there are several variants and causes of this disease, the common theme is having decreased clearance of apoB-containing particles, often but not always due to defective or absent LDL receptors, leading to the opposite problem from above.  Namely, these patients have a higher number of circulating LDL particles, and as a result a much higher incidence of atherosclerosis.

So why does having an LDL-P of 2,000 nmol/L (95^th percentile) increase the risk of atherosclerosis relative to, say, 1,000 nmol/L (20^th percentile)?  In the end, it’s a probabilistic game.  The more particles – NOT cholesterol molecules within the particles and not the size of the LDL particles – you have, the more likely the chance a LDL-P is going to ding an endothelial cell, squeeze into the sub-endothelial space and begin the process of atherosclerosis.

What about the other apoB containing lipoproteins?

Beyond the LDL particle, other apoB-containing lipoproteins also play a role in the development of atherosclerosis, especially in an increasingly insulin resistant population like ours.  In fact, there is some evidence that particle-for-particle Lp(a) is actually even more atherogenic than LDL (though we have far fewer of them).  You’ll recall that Lp(a) is simply an LDL particle to which another protein called apoprotein(a) is attached, which is both a prothrombotic protein as well as  a carrier of oxidized lipids – neither of which you want in a plaque. The apo(a) also retards clearance of Lp(a) thus enhancing LDL-P levels. It may foster greater penetration of the endothelium and/or greater retention within the sub-endothelial space and/or elicit an even greater immune response.

In summary

1. The progression from a completely normal artery to an atherosclerotic one which may or may not be “clogged” follows a very clear path: an apoB containing particle gets past the endothelial layer into the sub-endothelial space, the particle and its cholesterol content is retained and oxidized, immune cells arrive, an initially-beneficial inflammatory response occurs that ultimately becomes maladaptive leading to complex plaque.
2. While inflammation plays a key role in this process, it’s the penetration of the apoB particle, with its sterol passengers, of the endothelium and retention within the sub-endothelial space that drive the process.
3. The most numerous apoB containing lipoprotein in this process is certainly the LDL particle, however Lp(a) (if present) and other apoB containing lipoproteins may play a role.
4. If you want to stop atherosclerosis, you must lower the LDL particle number. Period.

(To Part V »)

Previously, in Part I and Part II of this series, we addressed 4 concepts:

   #1 — What is cholesterol?

   #2 — What is the relationship between the cholesterol we eat and the cholesterol in our body?

   #3 — Is cholesterol bad?

   #4 – How does cholesterol move around our body?

This week we’ll address the following concept:

   #5 – How do we measure cholesterol?

Quick refresher on take-away points from previous posts, should you need it

1. Cholesterol is “just” another fancy organic molecule in our body but with an interesting distinction: we eat it, we make it, we store it, and we excrete it – all in different amounts.
2. The pool of cholesterol in our body is essential for life.  No cholesterol = no life.
3. Cholesterol exists in 2 forms – unesterified or “free” (UC) and esterified (CE) – and the form determines if we can absorb it or not, or store it or not (among other things).
4. Much of the cholesterol we eat is in the form of CE. It is not absorbed and is excreted by our gut (i.e., leaves our body in stool). The reason this occurs is that CE not only has to be de-esterified, but it competes for absorption with the vastly larger amounts of UC supplied by the biliary route.
5. Re-absorption of the cholesterol we synthesize in our body (i.e., endogenous produced cholesterol) is the dominant source of the cholesterol in our body. That is, most of the cholesterol in our body is made by our body.
6. The process of regulating cholesterol is very complex and multifaceted with multiple layers of control.  I’ve only touched on the absorption side, but the synthesis side is also complex and highly regulated. You will see that synthesis and absorption are very interrelated.
7. Eating cholesterol has very little impact on the cholesterol levels in your body. This is a fact, not my opinion.  Anyone who tells you different is, at best, ignorant of this topic.  At worst, they are a deliberate charlatan. Years ago the Canadian Guidelines removed the limitation of dietary cholesterol. The rest of the world, especially the United States, needs to catch up.  To see an important reference on this topic, please look here.
8. Cholesterol and triglycerides are not soluble in plasma (i.e., they can’t dissolve in water) and are therefore said to be hydrophobic.
9. To be carried anywhere in our body, say from your liver to your coronary artery, they need to be carried by a special protein-wrapped transport vessel called a lipoprotein.
10. As these “ships” called lipoproteins leave the liver they undergo a process of maturation where they shed much of their triglyceride “cargo” in the form of free fatty acid, and doing so makes them smaller and richer in cholesterol.
11. Special proteins, apoproteins, play an important role in moving lipoproteins around the body and facilitating their interactions with other cells.  The most important of these are the apoB class, residing on VLDL, IDL, and LDL particles, and the apoA-I class, residing for the most part on the HDL particles.
12. Cholesterol transport in plasma occurs in both directions, from the liver and small intestine towards the periphery and back to the liver and small intestine (the “gut”).
13. The major function of the apoB-containing particles is to traffic energy (triglycerides) to muscles and phospholipids to all cells. Their cholesterol is trafficked back to the liver. The apoA-I containing particles traffic cholesterol to steroidogenic tissues, adipocytes (a storage organ for cholesterol ester) and ultimately back to the liver, gut, or steroidogenic tissue.
14. All lipoproteins are part of the human lipid transportation system and work harmoniously together to efficiently traffic lipids. As you are probably starting to appreciate, the trafficking pattern is highly complex and the lipoproteins constantly exchange their core and surface lipids. This is a big reason why measuring how much cholesterol is within various lipoprotein species will in many circumstances be so misleading, as we’ll discuss subsequently in this series.

Concept #5 – How do we measure cholesterol?

All this talk about cholesterol probably has some of you wondering how one actually measures the stuff.  Much of the raw content I’m going to present here is actually material I’ve had to learn recently.  One of the best resources I’ve found on this topic is the text book Contemporary Cardiology: Therapeutic Lipidology, in particular, chapter 14 by Tom Dayspring and chapter 15 by Bill Cromwell and Jim Otvos.  Anyone aspiring to be a lipid savant like these three pioneers probably ought to get a copy.  The other book that tells this story well is The Cholesterol Wars: The Skeptics versus the Preponderance of Evidence. For most folks, however, I’m hoping this series is sufficient and I’ll do my best to get the important points across.

As far back as the 1940’s scientists understood that cholesterol and lipids could not simply travel freely within the bloodstream without something to carry them and obscure their hydrophobicity, but it certainly wasn’t clear what these carriers looked like.

The initial breakthrough came during the Second World War when two researchers, E.J. Cohn and J.L. Oncley at Harvard developed a complex and elaborate technique to fractionate (i.e., separate) human serum (serum is blood, less the cells and clotting factors) into two “classes” of lipoproteins: those with alpha mobility and those with beta mobility.  [“Alpha” versus “beta” mobility describes a pattern of movement seen by different particles, relative to fluid, under a uniform electric field, which is the essence of electrophoresis.]

You’ll recall that LDL particles are also called “beta” particles and HDL particles are also called “alpha” particles.  Now you see why.

This work set the stage for subsequent work, by a physicist named John Gofman, using the techniques of preparative and analytic ultracentrifugation to fully classify the major classes of human lipoproteins. The table below summarizes what was gleaned by these experiments.

Cool, huh?  Well, sort of.  While this was an enormous breakthrough scientifically, it didn’t really have an inexpensive and quick test that could be used clinically the way, say, one could measure glucose levels or hemoglobin levels in patients routinely. What became crucial with Gofman’s discovery is that lipoproteins were now a recognized entity and they got their names according to their buoyancy: very low density, intermediate density, low density and high density.

There is more interesting history to this tale, but let’s fast-forward to where we are today.  When you go to your doctor to have your cholesterol levels checked, what do they actually do?

Let’s start at the finish line. What do they report? The figure below is a representative result.  It reports serum cholesterol (in total), serum triglycerides, HDL cholesterol (i.e., HDL-C), LDL cholesterol (i.e., LDL-C) and sometimes non-HDL-C (i.e., LDL-C + VLDL-C).  But where do these numbers come from?

Blood is drawn into a tube called a serum separator tube (SST) and immediately spun in centrifuge to separate the blood from “whole blood” into serum (normally clear yellow, top) and blood cells (dark red, bottom). A gel film, from the SST, separates the serum and blood cells, as shown below.  The tube is kept cool and sent from the phlebotomy lab to the processing lab.

As early as the 1950’s scientists figured out clever chemical tricks to directly measure the content of total cholesterol in the serum.  The chemical details probably are not interesting to non-chemists, but I was able to find a great paper from 1961 that details the methodology.  The point is this: initially it was only possible to measure the total content of cholesterol (TC), or concentration to be technically correct, in plasma. By that I mean it is the total mass (weight of all the cholesterol molecules) of cholesterol trafficked within all of the lipoprotein species that exist in a specified unit of volume: in the United States, we measure this in milligram of cholesterol per deciliter of plasma abbreviated as mg/dL, or in the rest of the world as mmol/Liter or mmol/L.  Why?  Think back to our analogy from last week:

Cholesterol is a passenger on a ship — the “ship,” of course, being a lipoprotein particle. The early methods of measuring cholesterol had to break apart the hull of the ship to quantify the cargo.  The assays to do so, like the one described above, were pretty harsh.  If you had a bunch of LDL ships, HDL ships, VLDL ships, and IDL ships, these assays ripped them all apart and told you the sum total of the cargo.  Obviously this was a great breakthrough in the day, but it was limited. From this assay, one could conclude, for example, that a person had 200 mg/dL of cholesterol hiding out in all their lipoprotein particles.

Good to know, but what next? It turns out there were two other important factors that could be measured directly in blood: triglycerides and the cholesterol content within the HDL particle, HDL-C. Early on laboratories could easily separate apoA-I-containing particles (i.e., HDL) from the apoB-containing particles (i.e., VLDLs, IDLs and LDLs), but they could not easily and economically separate the various apoB-containing particles from one another.  A full description of these methods is not necessary to appreciate this discussion, but for those interested, methodologies can be found here (TG) and here (HDL-C).

Important digression for context

What becomes critical to understand for our subsequent discussions is that the apoB particles have the potential to deliver cholesterol into an artery wall (the problem we’re trying to avoid), and 90-95% of the apoB particles are LDL particles.  Hence, it is LDL particle number (LDL-P or apoB) that drives the particles into the artery wall. Thus, physicians need to be able to quantify the number of LDL particles present in a given individual. For decades there was no way of doing that. Then LDL-C (read on) became available and it served as a way (not entirely accurate, but nonetheless a way) of quantitating LDL particles.

Back to the story

How can one figure out the concentration of cholesterol in the LDL particle? As you may recall from last week, LDL is the “ship” that carries the most cholesterol cargo. More importantly, as I mentioned above, it is also the key ship that traffics cholesterol directly into the artery wall. Thus, there has always been an enormous interest in knowing how much cholesterol is trafficked within LDL particles.

For a long time it was not possible to directly measure LDL-C, the cholesterol content of an LDL particle.  However, we did know the following had to be true:

          TC = LDL-C + HDL-C + VLDL-C + IDL-C + chylomicron-C + remnant-C + Lp(a)-C

where X-C denotes the cholesterol content of a respective cholesterol-carrying particle.  There are 2 particles in the equation above that I didn’t specifically mention last week, the remnant particle and the Lp(a) particle (pronounced “EL – pee – little – a,” which sounds less silly than, “Lip-a”). Lp(a) is an LDL-like particle but with a special apoprotein attached to it, aptly called apoprotein(a), which is actually “attached” to the apoB molecule of a standard LDL particle.  Think of Lp(a) as a “special” kind of LDL particle.  As we’ll learn later in this series, Lp(a) particles are bad dudes when it comes to atherosclerosis.

“Remnants” are nearly-empty-of-triglyceride particles of chylomicrons and VLDL.  In essence they are larger TG-rich particles that have lost a lot of their TG core content as well as surface phospholipids and are thus smaller than, or remnants of, their “parent particles.” Hence,they are cholesterol-rich particles. Under fasting conditions, in a not-too-terribly-insulin-resistant person, IDL-C, chylomicron-C, and remnant-C are negligible.  Furthermore, in most people Lp(a)-C does not exist or is not very high.

So we’re left with this simplification:

          TC ~ LDL-C + HDL-C + VLDL-C

which is clearly an improvement in convenience over the first equation.  But what to do about that pesky VLDL-C?

There are a number of variations, but essentially a breakthrough (mid 1970s) formula, called the Friedewald Formula, estimates VLDL-C as one-fifth the concentration of serum triglycerides (some variants use 0.16 instead of one-fifth, or 0.20).  This assumes all TG are trafficked in one’s VLDL particles and that a normally composed VLDL contains five times more TG than cholesterol.

Rearranging the above simplified formula we have:

           LDL-C ~ TC – HDL-C – TG/5

Let’s plug in the numbers from the above figure, as an example.  TC = 234 mg/dL; HDL-C = 48 mg/dL, and TG = 117 mg/dL.  Hence, LDL-C is approximately 234 – 48 – 117/5 = 163 mg/dL.

Kind of a long run for a short slide, huh? Perhaps, but it is important to understand that when you go to your doctor and get a “cholesterol test,” odds are this is exactly what you’re getting.

Therefore LDL-C can be estimated knowing just TC, HDL-C, and TG, assuming LDL-C matters (hint: it doesn’t matter much in many folks). 

Furthermore, what if the LDL particle is cholesterol-depleted instead of its normal state of being cholesterol-enriched?  Unfortunately, especially in an insulin resistant population (i.e., the United States), both TG content within lipoproteins and the exchange of TG for cholesterol esters between particles is very common, and using this formula can significantly underestimate LDL-C.  Worse yet, LDL-C becomes less meaningful in predicting risk, as I will address next week.

What about direct measurement of LDL-C?

To chronicle the entire history of direct LDL-C measurement is beyond the scope of this post.  Many companies have developed proprietary techniques to measure LDL-C directly, along with apoB, and ultimately LDL-P.  I’ll address two “major players” here: Atherotech and LipoScience.

Atherotech developed an assay, called a VAP panel (VAP stands for Vertical Auto Profile) to do everything described above, but also to directly measure the amount of cholesterol contained within the LDL particle.  Furthermore, they have developed assays to directly measure the cholesterol in IDL particles, VLDL particles, and even Lp(a) particles.  Below is a snapshot of how VAP reporting looks.

A couple of things are worth mentioning:

1. Subparticle cholesterol content information is also generated, including 2 different classes of HDL particles (HDL-2, HDL-3) and 4 different classes of LDL particles (LDL-1, LDL-2, LDL-3, LDL-4).
2. LDL particles, based on the subparticle information, are classified as “pattern A,” “pattern B,” or “pattern A/B.”  Pattern A implies more large, buoyant LDL particles, while pattern B implies more small, dense LDL particles.

Remember, though, while cholesterol mass concentration numbers may correlate with the number of particles, they often do not.  They only convey the mass concentration of cholesterol molecules within all of the particle subtypes per unit of volume.  VAP tests do not report the number of LDL or HDL particles, but they do attempt to estimate atherogenic particle number (apoB) using a proprietary formula based on subparticle cholesterol concentration and particle sizes.  I should point out that the formula, to my knowledge, has not been validated in any study and not published in a peer reviewed journal.

A high estimate of apoB100 (i.e., what the VAP reports) is said to correlate with the actual measurement of apoB.  Since apoB is found on each LDL particle, this serves as a proxy of LDL-P. The American Diabetic Associate and the American College of Cardiology Consensus Statement on Lipoproteins and the new National Lipid Association biomarker paper stipulates that apoB must be done using a protein immunoassay, not an estimate, such as that of VAP.

But how can one actually count the number of LDL particles and HDL particles?

There are several methods of doing this, but only one company, LipoScience, has the FDA approved technology to do so using nuclear magnetic resonance spectroscopy, or NMR for short. The other available methodologies are ion mobility transfer and ultracentrifugation (by Quest) and separation of LDL particles with particle staining (by Spectracell).  Virtually all guidelines (e.g., ADA, ACC, AACC and NLA) only advise LDL-P via NMR at this time.

NMR, which is the basis for not only how to count lipoprotein particles, but also diagnostic tests such as MRI scans, is really one of my favorite technical topics.  In residency I wrote a surgical handbook and on page145-146, if you’re interested, you can read a brief description of how MRI technology works, which will explain how NMR technology can actually count lipoprotein particles.

As an aside, and just to give you an idea of what a great sport my wife is, I wrote this surgical handbook over the course of a year while in residency.  To do so, I had to read approximately 8,000 pages of surgical textbooks and try to distill them down to just this 160 page summary.  Doing so required reading about 22 pages every day while working about 110 hours per week, typical of a surgical residency “back in the day.”  Besides exercising, I spent every single moment of my “free” time reading for and writing this handbook.  Finally, a few months into it, my wife asked, “Why the hell are you doing this?  You never watch TV, you never go out, you never do anything else!”  I responded that it was the best way I could learn this material, but also, that I wanted to have a legacy when I left residency.  Half joking, I asked her, “What’s your legacy?” Blank stare.  A few months later, for Valentine’s Day, she gave me this t-shirt. I think it’s safe to say not a single person has read this handbook.  So much for my legacy…

A brief explanation of how NMR works to count (and measure) particles can also be found here.

Below is a snapshot of how NMR reporting looks.  This particular report is from Health Diagnostics Laboratory (HDL), Inc.  LipoScience performs the actual NMR test, but HDL, Inc. runs a number of complimentary biomarkers I will discuss in subsequent posts.  I now use the HDL, Inc. test exclusively for reasons I will explain later.

In addition to counting the actual total number of LDL particles (LDL-P) and HDL particles (HDL-P) per liter, HDL, Inc. (not LipoScience) directly measures apoB and apoA-I.  Furthermore, the size of each particle is measured using NMR in nanometers (to give you a sense of how small these things are, and why we need to use nanometers to measure them, about 1.3 million LDL particles stacked side-by-side would measure only one inch).

The final point I’ll make about the value of NMR reported subparticle sizes and diameters is particularly telling when it comes to insulin resistance.  In the panel below, you can see that this person has small VLDL particles, small HDL particles, and LDL particles. Why is this interesting? The presence of increased large VLDL-P, large VLDL size, increased small LDL- P, small LDL size, reduced large HDL-P, small HDL size are early markers for insulin resistance, and such findings may actually precede more conventional signs of insulin resistance (insulin levels, glycemic abnormalities) by several years.  In other words, the number and size of the lipoprotein particles is perhaps the earliest warning sign for insulin resistance.

In summary

1. The measurement of cholesterol has undergone a dramatic evolution over the past 70 years with technology at the heart of the advance.
2. Currently, most people in the United States (and the world for that matter) undergo a “standard” lipid panel which only directly measures TC, TG, and HDL-C.  LDL-C can be measured directly, but is most often estimated.
3. More advanced cholesterol measuring tests do exist to directly measure LDL-C (though none are standardized), along with the cholesterol content of other lipoproteins (e.g., VLDL, IDL) or lipoprotein subparticles.
4. The most frequently used and guideline recommended test that can count the number of particles is the NMR LipoProfile.  In addition to counting the number of particles – the most important predictor of risk – NMR can also measure the size of each lipoprotein particle, which is valuable for predicting insulin resistance in drug naïve patients, before changes are noted in glucose or insulin levels.
   

I know some of you are getting antsy.  I thank you for your patience, and I hope you appreciate that it was a necessary step to get through this somewhat technical material and nomenclature.  Next week we’ll get to the “fun” stuff – what does all of this cholesterol have to do with heart disease?

In addition, we’ll get further into the importance of using LDL-P as the best predictor of risk.  If anyone wants to read up on another very important topic, especially for understanding why LDL-P is more important to know than LDL-C, get familiar with the concepts of discordant and concordant variables.  You’ll be hearing a lot about these.

(To Part IV »)

In this post I’m going to tackle the next set of logical (at least in my mind) questions to follow up on last week’s post, Part I in this series.

Last week we addressed these 3 concepts:

     #1 — What is cholesterol?

     #2 — What is the relationship between the cholesterol we eat and the cholesterol in our body?

     #3 — Is cholesterol bad?

This week we’ll address the following concept:

      #4 – How does cholesterol move around our body?

I want to thank folks for doing their best to resist the following two urges:

1. Please resist asking me questions beyond the scope of this post.  If it’s not in here, it will probably be in a subsequent post in this series.
2. Please resist sending me your cholesterol numbers.  Share your story with me and others, but understand that I can’t really comment other than to say what I pretty much say to everyone: standard cholesterol testing (including VAP) is of limited value and you should have a lipoprotein analysis using NMR spectroscopy (if you don’t know what I mean by this, that’s ok… you will soon). I can’t practice medicine over the internet.

Remember last week’s take away messages:

1. Cholesterol is “just” another fancy organic molecule in our body but with an interesting distinction: we eat it, we make it, we store it, and we excrete it – all in different amounts.
2. The pool of cholesterol in our body is essential for life.  No cholesterol = no life.
3. Cholesterol exists in 2 forms – unesterified or “free” (UC) and esterified (CE) – and the form determines if we can absorb it or not, or store it or not (among other things).
4. Much of the cholesterol we eat is in the form of CE. It is not absorbed and is excreted by our gut (i.e., leaves our body in stool). The reason this occurs is that CE not only has to be de-esterified, but it competes for absorption with the vastly larger amounts of UC supplied by the biliary route.
5. Re-absorption of the cholesterol we synthesize in our body (i.e., endogenous produced cholesterol) is the dominant source of the cholesterol in our body. That is, most of the cholesterol in our body was made by our body.
6. The process of regulating cholesterol is very complex and multifaceted with multiple layers of control.  I’ve only touched on the absorption side, but the synthesis side is also complex and highly regulated. You will discover that synthesis and absorption are very interrelated.
7. Eating cholesterol has very little impact on the cholesterol levels in your body. This is a fact, not my opinion.  Anyone who tells you different is, at best, ignorant of this topic.  At worst, they are a deliberate charlatan. Years ago the Canadian Guidelines removed the limitation of dietary cholesterol. The rest of the world, especially the United States, needs to catch up.  To see an important reference on this topic, please look here.

Concept #4 – How does cholesterol move around our body?

To understand how cholesterol travels around our body requires some understanding of the distinction between what is hydrophobic and hydrophilic.  A molecule is said to be hydrophobic  (also called nonpolar) if it repels water, while a molecule is said to be hydrophilic (also called polar) if it attracts water.  I could spend a lot of time getting in to the nuances of these properties, but I think it’s best to just focus on the major issues.  Think of your veins, arteries, and capillaries as the “waterways” or rivers of your body.

BONUS concept: Another important concept is that cell membranes are lipid bilayers (which are hydrophobic) as I wrote about last week.  Hence, a hydrophilic substance cannot pass through lipid membranes. Substances that can pass through lipid membranes are said to be lipophilic. A substance that has both polar (hydrophilic) and nonpolar (hydrophobic) properties is called amphipathic. The fact that unesterified cholesterol (UC) is an amphipathic molecule is a crucial property for its location in cell membranes. CE in which the –OH group has been replaced by a long chain fatty acid is a very nonpolar or hydrophobic molecule.

If a molecule needs to travel from your gastrointestinal tract (A) to, say, a cell in your quadriceps muscle (B) it needs to get on the river and travel from point A to point B.  Because blood is effectively water, (the “water” part of blood is called plasma, an aqueous solution with a bunch of “stuff” in it (e.g., red blood cells, white blood cells, other proteins, ions) there are two ways to move down the river – swim or hitch a ride on a boat.

If a molecule is hydrophilic, it can be transported in our bloodstream without any assistance – sort of like swimming freely in the river – because it is not repelled by water.  Conversely, if a molecule is hydrophobic, it must have a “transporter” to move about the river because the plasma (water) wants to repel it.  I know this seems like a strange concept, but if you think about it, you’ve already seen great examples in your day-to-day life:

Sugar and salt will easily dissolve in water.  They are, therefore, hydrophilic.  Oil does not dissolve in water.  It is, therefore, hydrophobic.

By extension, a molecule of glucose (sugar) or sodium and chloride ions (salt), because of their chemical properties which I won’t detail here, will travel through plasma without assistance.  A lipid will not.

All of this is a long way of saying that sterol lipids (of which cholesterol ester is the predominant form in plasma), because they are hydrophobic, need to be carried around our bloodstream.  They can’t move from one place to the next without a protein transporting molecule.

In other words, cholesterol doesn’t exist in our bloodstream without something to carry it from point A to point B.

So what are these “transporting molecules” called?

The proteins that traffic collections of lipids are called apoproteins. Once bound to lipids they are called apolipoproteins, and the protein wrapped “vehicle” that transports the lipids are called lipoproteins.  Many of you have probably heard this term before, but I’d like to ensure everyone really understands their important features.  A crucial concept is that, for the most part, lipids go nowhere in the human body unless they are a passenger inside a protein wrapped vehicle called a lipoprotein. As their name suggests lipoproteins are part lipid and part protein.   They are mostly spherical structures which are held together by a phospholipid membrane (which, of course, contains free cholesterol).  The figure below shows a schematic of a lipoprotein.

You will also notice variable-sized proteins on the surface of the lipid membrane that holds the structure together.  The most important of these proteins are called apolipoproteins, as I alluded to above.   The apolipoproteins on the surface of lipoprotein molecules serve several purposes including:

1. Assisting in the structural integrity and solubility of the lipoprotein;
2. Serving as co-factors in enzymatic reactions;
3. Acting as ligands (i.e., structures that help with binding) for situations when the lipoprotein needs to interact with a receptor on a cell.

Apolipoproteins come in different shapes and sizes which determine their “class.”  Without getting into the details of protein structure and folding, let me focus on two important classes: apolipoprotein A-I and apolipoprotein B.  Apoprotein A-I (abbreviated apoA-I), which is composed of alpha-helicies, form lipoproteins which are higher in density.  (The “A” class designation stems from the fact that apoA’s migrate with alpha-proteins in an electrophoretic field).  Conversely, apoprotein B (abbreviated apoB), which is predominantly composed of beta-pleated-sheets, form lipoproteins which are lower in density.  (The “B” class designation stems from the fact that apoB’s migrate with beta-proteins in an electrophoretic field.)

Virtually all apoB in our body is found on low-density lipoprotein – LDL, while most apoA-I in our body is found on high-density lipoprotein – HDL.  Going one step further, the main structural apoprotein on the LDL is called apoB100 (though we often shorten this to just “apoB”), and there is only one apoB molecule per particle. It’s starting to come together now with “high” and “low” density lipoproteins, isn’t it?

But there’s actually more to it.

Everything I just described above deals with the structure and surface of the lipoprotein molecule – sort of the like the hull of the ship.  But, what about the cargo?  Remember what started this discussion.  It’s all about transporting cholesterol (and lipids) which can’t freely travel in the bloodstream.  The “cargo” of these ships, what they actually carry both on their surface [molecules of cholesterol and phospholipids] and in their core [cholesteryl esters (CE) and triglycerides (TG, or triacylglycerols)] is what we’ll now turn our attention to.

The ratio of lipid-to-protein in the lipoprotein structure determines its density – which is defined as mass per unit volume.  Something that has a high density is heavier for a given volume than something with a low density.  The table in this link (which I’ve also included below) shows the relative density of the five main classes of lipoproteins (from most dense to least dense) as they were originally discovered using ultracentrifugation: high density lipoprotein (HDL), low density lipoprotein (LDL), intermediate density lipoprotein (IDL), very low density lipoprotein (VLDL), and chylomicron.

Note the very subtle difference in density between the most and least dense lipoprotein – about 10 or 15%.  Conversely, note the very large difference in diameter between each lipoprotein – as much as 2 orders of magnitude.  Later in this series, when we start to talk about the volume of a lipoprotein particle, this difference will be amplified 1,000 times (because volume is calculated to the third power of diameter).

Below is a figure I’ve borrowed graciously from one of Tom Dayspring’s remarkable lectures which gives you a sense of the diversity of each of these classes of lipoproteins as well as the subclasses within each class.  If this topic wasn’t confusing enough, there are actually multiple nomenclatures for the HDL subparticles.  Originally, nomenclature was based on their buoyancy.  Today nomenclature is based on the following methods, dependent on the technology used to measure them:

1. Particle separation using gradient gel electrophoretic fractionation (deployed by Berkeley Heart Lab).
2. Magnetic resonance assaying of lipid terminal methyl groups, called Nuclear Magnetic Resonance, or NMR (deployed by Liposcience).
3. Two-dimensional gradient gel electrophoresis and apoA-I staining (deployed by Boston Heart Lab).

We’ll cover this later, but I want to point this out now to avoid (unnecessary) confusion in the figure below, which uses the first two of these.

A few things probably jump out as you look at this figure:

1. ApoA-I lipoproteins (i.e., HDLs) are tiny compared to ApoB lipoproteins (i.e., VLDL’s, IDL’s, and LDL’s) [this figure is not actually to scale – the “real” difference is even more pronounced.]
2. As a general rule (with pathological exceptions), as particles move from being larger to smaller, the relative content of triglycerides (TG) goes down while the relative content of protein goes up, hence the density change.
3. Actual cholesterol mass is greatest in the LDL particle.
4. Each specific lipoprotein has a different core make up – meaning the variable ratio of TG to cholesterol ester changes. A particle of VLDL has 5 times more CE than TG whereas a particle of LDL typically has 4 or more times more CE than TG (i.e., ratio > 4:1), and an HDL has 90-95% CE and < 10% TG in its core.
5. The TG trafficking lipoproteins are chylomicrons from the intestine and VLDLs from the liver.

Deep breath. Anyone left wondering why this topic is NOT covered in medical school? I think I can conservatively say 95% to 99% of physicians do not know what you have just learned — not because they aren’t “smart,” but because this topic is simply not covered in medical school, and the pace at which the field is developing is too great for most doctors to keep up with.

Why is cholesterol concentration increasing and triglyceride concentration decreasing as lipoproteins progress from larger to smaller?

The liver exports VLDL which, after chylomicrons (used to get triglycerides to muscles and adipocytes and cholesterol from the gut to the liver) are the largest of the lipoprotein particles.  VLDL particles “give up” some of their triglycerides in the form of free fatty acids and shrink as they also release surface phospholipids. Once a certain size or buoyancy is reached it is called a “VLDL remnant” and ultimately an IDL.  Some (though not all) of the IDL particles undergo continued lipolysis to reduce in size and become the famous (or infamous) LDL particles.  However, most of the IDL particles are actually cleared by liver LDL receptors and do not become LDL particles. 

All along this process, the larger particles “shed” phospholipids and fatty acids and thus become cholesterol-rich.  It is the LDL particle that is the ultimate delivery vehicle of cholesterol back to the liver in a process now called “indirect reverse cholesterol transport.” However, under certain circumstances the LDL will penetrate and deliver its cholesterol load to the artery walls.  THIS IS EXACTLY WHAT WE DON’T WANT TO HAPPEN.  (Sorry for the bold ALL CAPS – I know some of you may have fallen asleep by now, but I didn’t want anyone missing the punch line.)  Because almost all cells in the body de-novo synthesize all the cholesterol they need, LDLs are not actually needed to deliver cholesterol to most cells.

The final important point I want to make about cholesterol transport is that it goes BOTH ways.  Lipoprotein particles carry triglycerides and cholesterol from the gut and liver to the periphery (muscles and adipocytes – fat cells) for energy, cellular maintenance, and other functions like steroid creation (called “steroidogenic” purposes – remember the figure last week showing a cholesterol molecule and steroid molecule).  Historically this process of returning cholesterol to the liver was thought to be performed only by HDL’s and has been termed reverse cholesterol transport (RCT) [you’ll need to subscribe -- for free -- to lecturepad.org to access this last link, which is well worth the time].

This RCT concept is outdated as we now know LDL’s actually perform the majority of RCT. While the HDL particle is a crucial part of the immensely complex RCT pathway, a not-so-well-known fact is that apoB lipoproteins (i.e., LDL’s and their brethren) carry most of the cholesterol back to the liver.  In other words, the “bad” lipoprotein, LDL, does more of the cleaning up (i.e., taking cholesterol back to the liver) than the “good” lipoprotein, HDL!

The problem, as we’ll discuss subsequently, is that LDL’s actually do the bad stuff, too – they dump cholesterol into artery walls.

Let’s put this all together to summarize how cholesterol gets around our body

1. Cholesterol and triglycerides are not soluble in plasma (i.e., they can’t dissolve in water) and are therefore said to be hydrophobic.
2. To be carried anywhere in our body, say from your liver to your coronary artery, they need to be carried by a special protein-wrapped transport vessel called a lipoprotein.
3. As these “ships” called lipoproteins leave the liver they undergo a process of maturation where they shed much of their triglyceride “cargo” in the form of free fatty acid, and doing so makes them smaller and richer in cholesterol.
4. Special proteins, apoproteins, play an important role in moving lipoproteins around the body and facilitating their interactions with other cells.  The most important of these are the apoB class, residing on VLDL, IDL, and LDL particles, and the apoA-I class, residing on the HDL particles.
5. Cholesterol transport occurs in both directions, towards the periphery and back to the liver.
6. The major function of the apoB-containing particles is to traffic energy (triglycerides) to muscles and phospholipids to all cells. Their cholesterol is trafficked back to the liver. The apoA-I containing particles traffic cholesterol to steroidogenic tissues, adipocytes (a storage organ for cholesterol ester) and ultimately back to the liver, gut, or steroidogenic tissue.
7. All lipoproteins are part of the human lipid transportation system and work harmoniously together to efficiently traffic lipids. As you are probably starting to appreciate, the trafficking pattern is highly complex and the lipoproteins constantly exchange their core and surface lipids. This is a big reason why measuring how much cholesterol is within various lipoprotein species will in many circumstances be so misleading, as we’ll discuss subsequently in this series.

This was a bit of a tough one, so let’s stop there.  Next week we’ll discuss how to actually measure cholesterol levels.  In other words, if you’re looking at the river, with all its floating ships carrying their cargo, how do we measure the amount of cargo actually contained within the ships?  Furthermore, is this the most important thing to be measuring?  Ironically, it’s easier to measure the cargo in the ships, but more important to know the number of ships in the river. But now I’m getting ahead of myself.

P.S. Happy Birthday Dad (now I’ll know if you’re reading my blog!)

(To Part III »)

I’ve been planning to write at length about this topic for a few months, but I’ve been hesitant to do so for several reasons:

1. To discuss it properly requires great care and attention (mine and yours, respectively).
2. My own education on this topic only really began about 9 months ago, and I’m still learning from my mentors at a geometric pace.
3. This topic can’t be covered in one post, even a Peter-Attia-who-can’t-seem-to-say-anything-under-2,000-word post.
4. I feel a bit like an imposter writing about lipidology because my mentors on this topic (below) have already addressed this topic so well, I’m not sure I have anything to add.

But here’s the thing.  I am absolutely – perhaps pathologically – obsessed with lipidology, the science and study of lipids.  Furthermore, I’m getting countless questions from you on this topic.  Hence, despite my reservations above, I’m going to give this a shot.

A few thoughts before we begin.

1. I’m not even going to attempt to cover this topic entirely in this post, so please hold off on asking questions beyond the scope of this post.
2. Please resist the urge to send me your cholesterol numbers.  I get about 30 such requests per day, and I cannot practice medicine over the internet.  By all means, share your story with me and others, but understand that I can’t really comment other than to say what I pretty much say to everyone: standard cholesterol testing (including VAP) is largely irrelevant and you should have a lipoprotein analysis using NMR spectroscopy (if you don’t know what I mean by this, that’s ok… you will soon).
3. This topic bears an upsettingly parallel reality to that of nutrition “science” in that virtually all health care providers have no understanding of it and seem to only reiterate conventional wisdom (e.g., “LDL is bad,” “HDL is good”).  We’ll be blowing the doors off this fallacious logic.

By the end of this series, should you choose to internalize this content (and pick up a few homework assignments along the way), you will understand the field of lipidology and advanced lipid testing better than 95% of physicians in the United States.  I am not being hyperbolic.

One last thing before jumping in:  Everything I have learned and continue to learn on this topic has been patiently taught to me by the words and writings of my mentors on this subject: Dr. Tom Dayspring, Dr. Tara Dall, Dr. Bill Cromwell, and Dr. James Otvos. I am eternally in their debt and see it as my duty to pass this information on to everyone interested.

Are you ready to start an exciting journey?

Concept #1 – What is cholesterol?

Cholesterol is a 27-carbon molecule shown in the figure below. Each line in this figure represents a bond between two carbon atoms.  Sorry, I’ve got to get it out there.  That’s it.  Mystery over.

All this talk about “cholesterol” and most people don’t actually know what it is.  So there you have it.  Cholesterol is “just” another organic molecule in our body.

I need to make one important distinction that will be very important later.  Cholesterol, a steroid alcohol, can be “free” or “unesterified” (“UC” as we say, which stands for unesterified cholesterol) which is its active form, or it can exist in its “esterified” or storage form which we call a cholesterol ester (“CE”).  The diagram above shows a free (i.e., UC) molecule of cholesterol.  An esterified variant (i.e., CE) would have an “attachment” where the arrow is pointing to the hydroxyl group on carbon #3, aptly named the “esterification site.”

Since cholesterol can only be produced by organisms in the Animal Kingdom it is termed a zoosterol. In a subsequent post I will write about a cousin of cholesterol called phytosterol, but at this time I think the introduction would only confuse matters.  So, if you have a question about phytosterols, please hang on.

Concept #2 – What is the relationship between the cholesterol we eat and the cholesterol in our body?

We ingest (i.e., take in) cholesterol in many of the foods we eat and our body produces (“synthesizes”) cholesterol de novo from various precursors.   About 25% of our daily “intake” of cholesterol – roughly 300 to 500 mg — comes from what we eat (called exogenous cholesterol), and the remaining 75% of our “intake” of cholesterol — roughly 800 to 1,200 mg – is made by our body (called endogenous production).  To put these amounts in context, consider that total body stores of cholesterol are about 30 to 40 gm (i.e., 30,000 to 40,000 mg) and most of this resides within our cell membranes.  Every cell in the body can produce cholesterol and thus very few cells actually require a delivery of cholesterol. Cholesterol is required by all cell membranes and to produce steroid hormones and bile acids.

Of this “made” or “synthesized” cholesterol, our liver synthesizes about 20% of it and the remaining 80% is synthesized by other cells in our bodies.  The synthesis of cholesterol is a complex four-step process (with 37 individual steps) that I will not cover here (though I will revisit), but I want to point out how tightly regulated this process is, with multiple feedback loops.  In other words, the body works very hard (and very “smart”) to ensure cellular cholesterol levels are within a pretty narrow band (the overall process is called cholesterol homeostasis).  Excess cellular cholesterol will crystalize and cause cellular apoptosis (programmed cell death). Plasma cholesterol levels (which is what clinicians measure with standard cholesterol tests) often have little to do with cellular cholesterol, especially artery cholesterol, which is what we really care about. For example, when cholesterol intake is decreased, the body will synthesize more cholesterol and/or absorb (i.e., recycle) more cholesterol from our gut. The way our body absorbs cholesterol is so amazing, so I want to spend a bit of time discussing it.

In medical school, whenever we had to study physiology or pathology I always had a tendency to want to anthropomorphize everything. It’s just how my brain works, I guess, and understanding cholesterol absorption is a great example of this sort of thinking.  The figure below shows a cross-section of a cell in our small intestine (i.e., our “gut”) called an enterocyte that governs how stuff in our gut actually gets absorbed.  The left side with the fuzzy border is the side facing the “lumen” (the inside of the “tube” that makes up our gut).  You’ll notice two circles on that side of the cell, a blue one and a pink one.

[What follows is a bit more technical than I would have liked, but I think it’s very important to understand how this process of cholesterol absorption works.  It’s certainly worth reading this a few times to make sure it sinks in.]

• The blue circle represents something called a Niemann-Pick C1-like 1 protein (NPC1L1).  It sits at the apical surface of enterocytes and it promotes active influx (i.e., bringing in) of gut luminal unesterified cholesterol (UC) as well as unesterified phytosterols into the enterocyte.  Think of this NPC1L1 as the ticket-taker at the door of the bar (where the enterocyte is the “bar”); he lets most cholesterol (“people”) in.  However, NPC1L1 cannot distinguish between cholesterol (“good people”) and phytosterol (“bad people” – I will discuss these guys later, so no need to worry about it now) or even too much cholesterol (“too many people”). [I can’t take any credit for this anthropomorphization – this is how Tom Dayspring explained it to me!]
• The pink circle represents an adenosine triphosphate (ATP)-binding cassette (ABC) transporters ABCG5 and ABCG8.  This complex promotes active efflux (i.e., kicking out) of unesterified sterols (cholesterol and plant sterols – of which over 40 exist) from enterocytes back into the intestinal lumen for excretion.  Think of ABCG5,G8 as the bouncer at the bar; he gets rid of the really bad people (e.g., phytosterols as they serve no purpose in humans) you don’t want in the bar who snuck past the ticket-taker (NPC1L1).  Of course in cases of hyperabsorption (i.e., in cases where the gut absorbs too much of a good thing) they can also efflux out un-needed cholesterol.  Along this analogy, once too many “good people” get in the bar, fire laws are violated and some have to go. The enterocyte has “sterol-excess sensors” (a nuclear transcription factor called LXR) that do the monitoring and these sensors activate the genes that regulate NPC1L1 and ABCG5,G8).

There is another nuance to this, which is where the CE versus UC distinction comes in:

• Only free or unesterified cholesterol (UC) can be absorbed through gut enterocytes.  In other words, cholesterol esters (CE) cannot be absorbed because of the bulky side chains they carry.
• Much (> 50%) of the cholesterol we ingest from food is esterified (CE), hence we don’t actually absorb much, if any, exogenous cholesterol (i.e., cholesterol in food).  CE can be de-esterified by pancreatic lipases and esterolases – enzymes that break off the side branches and render CE back to UC — so some ingested CE can be converted to UC.
• Furthermore, most of the unesterified cholesterol (UC) in our gut (on the order of about 85%) is actually of endogenous origin (meaning it was synthesized in bodily cells and returned to the liver), which ends up in the gut via biliary secretion and ultimately gets re-absorbed by the gut enterocyte.  The liver is only able to efflux (send out via bile into the gut) UC, but not CE, from hepatocytes (liver cells) to the biliary system.  Liver CE cannot be excreted into bile. So, if the liver is going to excrete CE into bile and ultimately the gut, it needs to de-esterify it using enzymes called cholesterol esterolases which can convert liver CE to UC.
• Also realize that the number one way for the liver to rid itself of cholesterol is to convert the cholesterol into a bile acid, efflux that to the bile (via a transporter called ABCB11) and excrete the bile acids in the stool (typically most bile acids are reabsorbed at the ileum).

Concept #3 – Is cholesterol bad?

One of the biggest misconceptions out there (maybe second only to the idea that eating fat makes you fat) is that cholesterol is “bad.”  This could not be further from the truth.  Cholesterol is very good!  In fact, there are (fortunately rare) genetic disorders in which people cannot properly synthesize cholesterol.  Once such disease is Smith-Lemli-Opitz syndrome (also called “SLOS,” or 7-dehydrocholesterol reductase deficiency) which is a metabolic and congenital disorder leading to a number of problems including autism, mental retardation, lack of muscle, and many others.

Cholesterol is absolutely vital for our existence.  Let me repeat: Cholesterol is absolutely vital for our existence. Every cell in our body is surrounded by a membrane.  These membranes are largely responsible for fluidity and permeability, which essentially control how a cell moves, how it interacts with other cells, and how it transports “important” things in and out. Cholesterol is one of the main building blocks used to make cell membranes (in particular, the ever-important “lipid bilayer” of the cell membrane).

Beyond cholesterol’s role in allowing cells to even exist, it also serves an important role in the synthesis of vitamins and steroid hormones, including sex hormones and bile acids.  Make sure you take a look at the picture of steroid hormones synthesis and compare it to that of cholesterol (above). If this comparison doesn’t convince you of the vital importance of cholesterol, nothing I say will.

One of the unfortunate results of the eternal need to simplify everything is that we (i.e., the medical establishment) have done the public a disservice by failing to communicate that there is no such thing as “bad” cholesterol or “good” cholesterol.  All cholesterol is good!

The only “bad” outcome is when cholesterol ends up inside of the wall of an artery, most famously the inside of a coronary artery or a carotid artery, AND leads to an inflammatory cascade which results in the obstruction of that artery (make sure you check out the pictures in the links, above). When one measures cholesterol in the blood – we really do not know the final destination of those cholesterol molecules!

And that’s where we’ll pick it up next time – how does “good” cholesterol end up in places it doesn’t belong and cause “bad” problems?  If anyone is looking for a little extra understanding on this topic, please, please, please check out my absolute favorite reference for all of my cholesterol needs, LecturePad. It’s designed primarily for physicians, but I suspect many of you out there will find it helpful, if not now, certainly once we’re done with this series.

To summarize this somewhat complex issue

1. Cholesterol is “just” another fancy organic molecule in our body, but with an interesting distinction: we eat it, we make it, we store it, and we excrete it – all in different amounts.
2. The pool of cholesterol in our body is essential for life.  No cholesterol = no life.
3. Cholesterol exists in 2 forms – UC and CE – and the form determines if we can absorb it or not, or store it or not (among other things).
4. Most of the cholesterol we eat is not absorbed and is excreted by our gut (i.e., leaves our body in stool). The reason is it not only has to be de-esterified, but it competes for absorption with the vastly larger amounts of UC supplied by the biliary route.
5. Re-absorption of the cholesterol we synthesize in our body is the dominant source of the cholesterol in our body. That is, most of the cholesterol in our body was made by our body.
6. The process of regulating cholesterol is very complex and multifaceted with multiple layers of control.  I’ve only touched on the absorption side, but the synthesis side is also complex and highly regulated. You will discover that synthesis and absorption are very interrelated.
7. Eating cholesterol has very little impact on the cholesterol levels in your body. This is a fact, not my opinion.  Anyone who tells you different is, at best, ignorant of this topic.  At worst, they are a deliberate charlatan. Years ago the Canadian Guidelines removed the limitation of dietary cholesterol. The rest of the world, especially the United States, needs to catch up.

(To Part II »)

For the sake of this discussion, let’s ignore the fact that the “historically” lean countries (e.g., France, Italy, Japan) are catching up to our levels of obesity and metabolic syndrome, especially in certain affluent subsets.  After all, we did get a 40 year head start on how to eat poorly.   So, let’s ask the question this way:

How does the average person living in, say, Japan stay leaner and healthier than the average American while still consuming >70% of their caloric intake in the form of carbohydrates?  

I don’t claim to know the answer this question, but I’ve got a few ideas.

Before getting to this question I want to mention that I have reorganized a page on the blog, Media, which now has a lot of videos and interviews.  A lot of the questions I get asked are addressed in these videos and interviews (both of me and others), so please check there for answers to your questions. Last week I was interviewed by Ben Greenfield. Ben asked a lot of great questions which many of you have also asked over the past few months. Take a look here and see the questions Ben posed.  If you’re interested in hearing my thoughts, listen to the audio clip from the interview.

Back to the question at hand

These data are a bit dated, but you can see the point: the United States is leading the way in the obesity race, while other countries (including those eating at least as high a total percent of their intake from carbohydrates) are not.  How is this possible if insulin – stimulated by carbohydrate intake – is an important hormone in the body’s drive to accumulate fat?  

This problem has many layers to it, but for the purpose of simplicity (always a danger when aspiring to explain complex phenomena) I’ll limit the discussion to three main points – think of them as the “higher order terms” – in their order of importance.

1. Lower consumption of sugar
2. Lower absolute consumption of carbohydrates
3. More favorable consumption of polyunsaturated fatty acids (PUFA)

These reasons are not independent.  In other words, they are highly correlated and linked to each other, which actually amplifies their effects.

One other point to keep in mind: There is no definitive experiment I will point to that can prove my assertion beyond a reasonable doubt – for that I would need a prospective, well-controlled experiment comparing the eating habits of these countries over decades.  Many things I’m discussing are observational in nature, so you’ll have to really scrutinize my thesis on your own. [SURGEON’S WARNING: Uncharacteristic cheap-shot coming up.]  I don’t want to commit the same errors in logic that folks like Colin Campbell and Walter Willett commit for a living.

Reason #1 — Sugar intake

There is a great disparity between U.S. sugar consumption and the sugar consumption of countries like France, Italy, and Japan (and most countries, actually).  When I say “sugar,” of course, I mean sucrose, high fructose corn syrup, beet sugar, cane sugar, and liquid fructose (e.g., fruit juice) to name just a few forms.  Why does this matter?  If you’re not currently up on the why-sugar-is-bad-for-you data, it’s worth reading this post, and watching the lecture by Dr. Lustig.  For a quicker answer, watch this video from 60 Minutes.

Think of sugar as a “metabolic bully” or the proverbial Trojan Horse of metabolic syndrome – you let sugar in, and before you know it, you have diabetes, heart disease, and cancer.  Consumption of sugar makes us metabolically inflexible as part of a vicious cycle I’ve diagrammed below.  The more sugar you eat, the more insulin resistant you become.  The more resistant you are to the effects of insulin, the more insulin your pancreas needs to secrete in response to all carbohydrates, including the not-so-bad “non-sugar” ones. The more insulin your pancreas needs to secrete to manage your glycemic load, the higher your average insulin levels, which is manifested by higher levels of circulating insulin at all times – fed and not fed. Higher levels of insulin lead to less fat oxidation and more fat storage (from both ingested fats AND ingested carbohydrates – de novo lipogenesis).  This, not surprisingly, leads to greater insulin resistance, and so the cycle continues.  There is a reason “vicious cycles” are called “vicious.”

Reason #2 — Total glycemic load

It’s important to keep in mind that the percent of carbohydrate consumed is nowhere near as important as the absolute amount of carbohydrate consumed. Failure to understand this point may be one of the most significant reasons for the calories-are-everything-argument.  Recall my post on why Weight Watchers and most commercial diets are actually low-carb diets.  Virtually any diet that reduces caloric intake also reduces glycemic load.  Worth repeating: Virtually any diet that reduces caloric intake also reduces glycemic load. That is, cutting calories almost always means cutting carbohydrates, cutting insulin, and cutting fat storage.  So what does this have to do with folks in Japan eating rice?  While these cultures may consume a higher percentage of their intake from carbohydrates, their actual glycemic load is lower. In other words, they actually consume fewer total carbohydrates in most cases than a typical Westerner (and in the presence of much less sugar!).  Contrast “typical” carbohydrates consumed by these “high” carbohydrate societies:

Sure, they eat rice and bread and pasta.  But how much at one time?  And what are they eating it with?

Compare the figure above with that below, showing “typical” American carbohydrate consumptive patterns:

Are we eating the same amount of pasta per meal as the folks in Italy?  Perhaps, though I don’t think so.  Furthermore, while they make their own pasta sauce out of home-grown tomatoes, garlic, and olive oil, we dump a pound of Prego on ours (the second or third ingredient is nearly always sugar).  While the French are eating baguettes, we’re eating sugar-filled bread.  While the Japanese are eating a small bowl of rice, we’re stuffing our face with a plate of fries and breaded onion rings.

Why does consuming more glucose matter, notwithstanding the point that the glucose we consume is virtually always linked to sugar?  The human body can only store a finite amount glycogen, so any excess glucose we ingest actually does 2 harmful things:

1. Continues to raise insulin levels, which inhibits fat mobilization,  and
2. Gets stored as fatty acid, and ultimately ends up as triglyceride in fat cells.  Remember, this is a one-way metabolic street.  When your body turns glucose into fat (technically, we turn acetyl-CoA into malonyl-CoA into palmitate), you can’t turn that fat back into glycogen.

More absolute glucose, regardless of the relative percent, still leads to more fat accumulation.

Reason #3 — Inflammation

While insulin is certainly near the top of the list of pro-inflammatory factors in our bodies, it’s important to keep in mind the role of some other factors whose balance plays a role in inflammation such as eicosapentaenic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (AA) to name a few.  I will, in a separate dedicated post, compose a thorough discussion on the metabolism of omega-3 and omega-6 fatty acids. To be clear, the science around this is not fully worked out, and much of what we speculate is based on indirect cause-and-effect inference, coupled with “sound” mechanistic reasoning and, of course, strong observation.  In other words, this is not close to bulletproof logic.

What is known is that diets high in omega-6 polyunsaturated fatty acid (PUFA) (e.g., mostly plant oils like sunflower, canola, safflower, and corn oil) relative to omega-3 PUFA (e.g., fish and fish oils) create a disproportionate ratio of AA to EPA and DHA. When I go through the biochemistry of this (which is super-cool!) it will be obvious why this is true: Eat a huge excess of omega-6 PUFA relative to omega-3 PUFA and your blood and tissues will show a lot of AA relative to EPA and DHA.  Same logic holds in reverse.

What does this mean?

Here’s where the story goes from being “clear” to “less clear,” at least to me. There is reasonable evidence that too little EPA and DHA (omega-3) predisposes us to certain diseases, in particular, cardiovascular disease.  There is some evidence that the relative amounts of EPA to AA and DHA to AA matter, too (i.e., what happens when you eat too much omega-6 PUFA relative to omega-3 PUFA).  What is not clear is if too much AA relative to EPA and DHA (i.e., much more omega-6 than omega-3) leads to clinically significant inflammation in the body that fosters other disease states.  In fact, a case can be made that high amounts of omega-3 PUFA are outright protective from many diseases including the disease spectrum of metabolic syndrome (e.g., diabetes, heart disease, cancer, Alzheimer’s disease), independent of omega-6 PUFA intake.

Observationally, this seems “clear” – societies whose ratio of omega-6 to omega-3 consumption are lowest (e.g., 3-to-1 or better) have far less disease than societies whose ratio is much higher in favor of omega-6 (e.g., 30-to-1).  Of course, this does not prove anything, since uncontrolled observations are just that.  This is how folks like Ancel Keys and Colin Campbell have caused so much trouble and confusion in the field of nutrition.  It is possible that some other factor, beyond this, is resulting in the differential disease pattern.   In other words, it is not clear if this observation is correct because of the relative amounts of omega-3 and omega-6, OR if it is true because of the absolute amount of omega-3, OR if it is true for some other reason? I don’t know (yet), but will continue to work on this.

That said, there is some indirect evidence linking differential consumption of PUFA (i.e., relative differences in omega-3 versus omega-6) with actual disease states.  A paper published in 1993 in the New England Journal of Medicine showed that patients with more EPA/DHA precursors than AA precursors in cell membranes had greater insulin sensitivity and less heart disease (though, obviously, these are linked).  I will review this in much greater detail in a dedicated omega-3/omega-6 post, but I want to point out that there is some evidence beyond just the observational data suggesting more omega-3 and less omega-6 in your diet leads to better insulin sensitivity:

Eating more omega-3 and less omega-6 may lead to more EPA/DHA precursors in cell membranes than AA precursors, which is correlated [not causally linked] with less insulin resistance.

Hence, Western diets, where we don’t consume much omega-3 PUFA, and it is very difficult to avoid omega-6 PUFA (they show up in virtually every processed and packaged food we touch, not to mention all sauces and dressing, and even our grain-fed meat), may predispose us to greater insulin resistance and inflammation.  As you can see in the figure below, a (historically) typical Japanese diet was nearly equal in omega-6 to omega-3, while our diets are typically much higher in omega-6 than omega-3 – BOTH because we don’t eat much omega-3 AND because we eat much more omega-6.  The same is true of a traditional Mediterranean diet.

Let me reiterate: I do not know if the relevant issue is the denominator (i.e., absolute amount of omega-3 consumed) or the ratio (i.e., relative amount of omega-6 to omega-3).

[Personal note: Pending resolution, I do both: I maximize my omega-3 intake and minimize my omega-6 intake to a ratio of about 1:1 with lots of EPA and DHA and little omega-6.  What is not clear to me yet from current data is if I should be minimizing my omega-6 intake.]

What can we learn from this?

I alluded to how multifactorial this issue was, but I hope it’s clearer to you now.  Let me try to summarize why some cultures have historically been able to consume rice and pasta and baguettes but stay leaner and healthier than Americans:

1. They consume a fraction of the sugar we do.  More sugar consumption leads to greater insulin resistance, more fat creation, less fat breakdown, and more fat accumulation.
2. They consume less total glucose, AND the glucose they consume is accompanied by less sugar (and less omega-6 PUFA, if it matters).
3. They consume a ratio of omega-6 to omega-3 PUFA that is much lower than we do.  This may further reduce any insulin resistance brought on by the glucose they do consume (in smaller doses and with less sugar).

Let me close with one personal and anecdote.  When I began my nutritional journey, for over 18 months I still consumed a modest amount of carbohydrate, probably on the order of what a typical person in Japan would consume.  The biggest elimination in my diet was sucrose, HFCS, and “junk” carbohydrates. The results were impressive.  I went from being about 200 pounds at 25% body fat to being 177 pounds at 10% body fat while still consuming some carbohydrates (by that point I was down to maybe 100-150 gm per day).   However, I was able to get leaner (170 pounds, 7.5% body fat) and further improve my risk profile for disease by going below 50 gm per day (i.e., entering nutritional ketosis).  Was this last step of nutritional ketosis necessary? Of course not, but it was a nice way to experience the full spectrum of carbohydrate restriction.  Will I ever go back to eating 100-150 gm per day of the “right” carbohydrates at some point? Probably, provided I don’t go back to eating sugar and stuffing my face with carbohydrates.  It will depend on what I’m optimizing for.

My point is this: Just modifying your diet by the 3 factors I mention in this post — elimination of sugar, less total glucose load, and improved omega-3/omega-6 profile — even if you are not genetically programmed to be lean, will probably deliver 80% of the value in terms of disease risk and body composition.

Is carbohydrate reduction or outright restriction “right” for everyone?  I doubt it.  Besides oxygen and water the list of “universal truths” for human health is pretty short.  Parenthetically, one can still overdose on both oxygen and water – in other words, even these two completely essential compounds can be toxic outside of their ideal ranges.

If you’ve been following this blog and/or this general discussion, you’ve probably asked yourself the question I’m about to pose.  If you haven’t asked it yourself, you’ve likely been asked by someone as you’ve had the discussion with friends or family.  Here’s the question:

If insulin is so important in regulating fat metabolism, why do some people eat whatever they want and not get fat? Conversely, why do some people following the strictest carbohydrate-reduced diet remain fat?

This is a paramount question, and I’m sorry it’s taken me four months to finally get to it.  Before we do get to it let me digress (seemingly) to discuss gravity.  If you know everything about gravitational forces, feel free to skip this section.

What is gravity?

For the purpose of simplicity I will limit this discussion to Newton’s law of universal gravitation, as it applies to virtually any “gravity scenario” we encounter in our lives, and it’s the law everyone thinks of when they hear the word “gravity.”  Newton’s law of universal gravitation states that every mass in the universe attracts every other mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

For those, like me, who love equations, here it is:

In this equation, m1 and m2 are the masses of the two spheres, and r is the distance between them.  G is a really, really, really tiny number called the gravitational constant which, as its name suggests, is a constant.

In other words, objects in the universe have attractive forces between them. These attractive forces depend on two things: the masses of the objects (the more the mass, the more the force, since mass is in the top of the equation) and the distance between them (the more the distance between them, the less the force, since distance – squared – is in the bottom of the equation).  No other amount of detail is really necessary to understand the point I’m going to make.

For most objects on earth (excluding the earth), this force of gravitation is actually not particularly dominant.  When I’m standing next to someone, neither of us can feel this force for two reasons: 1) our masses are not high enough, and 2) the distance between us is too great to overcome the really, really, really tiny gravitational constant.  For example, two 80 kg people standing even 1 cm apart only exert 0.004 Newtons on each other, which is completely unnoticeable.  [A Newton is the unit we use to measure force.]

It turns out for most objects on earth that we interact with, gravitational force is irrelevant (actually, it’s what we’d call a “higher order term” if you remember my discussion of ordered terms, or relative importance from this post).  But there is one enormous exception: the earth!  Because the earth weighs so much (about 6 trillion trillion kilograms; no, that’s not a typo – 6 followed by 24 zeros) for pretty much any object on earth ranging from a feather to a 747 to a skyscraper, the force the earth exerts on us (and us back on her) is equal to our own mass multiplied by 9.8 meters per second per second (this number is the acceleration we experience due to gravity).  You can verify this for yourself using the equation above (plug in your mass, the mass of the earth, and the distance from you to the center of the earth).

This is a long way of getting to one of the most often experienced applications of Newton’s Second Law: the net force that acts on a body is equal to the mass of that body multiplied by the change in the mass’s velocity (referred to as acceleration).   When you drop an object, the earth is pulling it towards itself with a force equal to the mass of object multiplied by 9.8 meters per second per second (this unit of m/s/s is the unit for acceleration – the rate of change of velocity).

Here’s a more visceral example: When you are in an airplane taking off on the runway you feel an enormous force on your back, though you’re traveling much slower than when in full flight, when you feel nothing.  Why? In full flight acceleration is zero – velocity, albeit high, is constant – so you feel no force.  On the runway, the plane is accelerating (i.e., changing velocity), so you feeeeel it.

Why did I just explain all of this?

We live in a world that is governed by physical laws, of which Newton’s laws are but an important subset.  Do you need to know them?  Nope.  Does understanding them change them?  Nope.  Can you “will” your way out of them? Nope.  Is it better to know them or be completely oblivious of them?  I guess it depends on your personality.  I prefer to know as much as possible about the physical world I live in.  It keeps me safe.

Some of you know everything about gravity that I just explained, and then some.  Some of you just heard it for the first time.  Regardless, the laws of gravitation are universally true and apply to every single one of us, whether we like or are aware of it or not.  Let’s consider a few examples.

Look at this fellow:

Or this fellow:

Are they “defying gravity?”

Are they experiencing a “different” form of gravity than, say, this fellow?

Or this fellow?

Not at all.  In fact, each of these four men is actually subject to the exact same universal truth of gravity.  So, why do the first two appear to challenge the law of gravity while the second two appear to exaggerate the law of gravity?

Lots of reasons, probably, but the two most obvious are differences in genetics and differences in conditioning.  No matter how you slice it, Michael Jordan was a completely gifted athlete.  He also outworked virtually everyone, and if you subscribe to the theories of Daniel Coyle, as described in The Talent Code, these two features are complexly weaved together.   What about the guy falling off the picnic table or the guy belly flopping into the pool? Not quite the same genes and nowhere near the same level of conditioning.  As a result, the impact of gravity is more obvious on them.

Here’s another example:  Consider a ledge 10 feet off the ground.  Let’s line these three gentlemen up and ask each of them to jump off the exact same ledge.

The same law of gravity applies to each of them. No exceptions. Will they all experience the law of gravity in the same way?  Of course, not.  First guy – no problem.  Second guy – probably breaks his leg.  Third guy – probably dies.

Let’s add one more layer of complexity to this.  When I was 16 years old, I could jump off a 10 foot ledge with zero difficulty.  Today, at 39, it would take a bit of practice and a lot of concentration to avoid spraining my ankle and tearing a ligament in my knee.  When I’m 65, I’ll be lucky not to break my leg.  When I’m 85, I’ll be lucky not to break my neck.  Why?  Same gravity, right?  Same genes, right? Yet over time, I will experience gravity differently.  Changes in my body over time lead to a differential experience of the same physical laws.

How does insulin fit into this discussion?

Insulin is the most important hormone in our body when it comes to fat mobilization (breakdown) and fat storage.  This is a fact.  There is not one person who studies the endocrine system who will not acknowledge the following quote from Lehninger’s Principles of Biochemistry (the “bible” of biochemistry).

“High blood glucose elicits the release of insulin, which speeds the uptake of glucose by tissues and favors the storage of fuels as glycogen and triglycerides, while inhibiting fatty acid mobilization in adipose tissue.”

In other words, eating glucose (carbohydrates) increases insulin levels in our body.  Insulin drives glucose into liver and muscle cells as glycogen (in small, finite amounts) and into fat cells as triglycerides (in unlimited amounts). Insulin also inhibits the breakdown and utilization of fat, as shown here.

Insulin does not act alone, and the story of fat storage and breakdown is complex if you want to understand every single detail, but the “first order term” is insulin.  I will spend time in the future writing about insulin’s “dance partner,” leptin.  But insulin is probably the General when it comes to determining how the body partitions fat.

So, insulin is sort of like gravity.  It’s in your body whether you know about it or not.  It’s acting on your cells whether you like it or not.  It’s playing a major role in determining your ability to mobilize versus store fat if you believe me or not.

Does this mean insulin has the same effect on everyone?  Does this mean insulin has the same effect on any given person over time? Of course not. Contrast me and my wife.  I look at carbohydrates and start to store fat. If you want a reminder of what I looked like on an “athlete’s diet” of complex carbs and little saturated fat, coupled with 3 to 4 hours of exercise a day, look here, here, and here.  On the other hand, my wife can eat a bag of Oreo cookies for dinner every night, coupled with all the pasta, bread, and rice the world has to offer and not put on one pound (she has weighed about 110 pounds her entire adult life).  How is this possible?  Does this mean insulin doesn’t control fat metabolism?  No, it means we have an entirely different genetic make-up.  Her grandmother is 86 years old, eats bread all day long, is healthy as a horse, and weighs 100 pounds. Conversely, I come from a family where every single man has died of heart disease and looked like the Pillsbury Dough Boy prior to doing so.  I’m genetically programmed to lean towards metabolic syndrome, but I’ve been able to reverse it through strict attention to my eating habits.

This isn’t unique to me and my wife. There is an entire spectrum – a distribution across the population – of people with varying degrees of susceptibilities to the effects of carbohydrate on insulin levels and the commensurate effects of insulin levels on fat storage and breakdown.

And like gravity, the effect of insulin on our metabolism of fat changes over time at the individual level, usually for the worse.

Consider, again, my example: When I was 16 years old I weighed 160 pounds, had between 4 and 5% body fat, a 28-inch waist and a 44-inch chest.  Breakfast consisted of a box (not a bowl) of cereal.  Lunch consisted of 7 turkey and tuna sandwiches (yes, 14 pieces of bread), a gallon of apple juice, and a plate of fries and gravy.  Dinner was a pound of pasta and half a chicken.  Despite eating over 1,000 gm of carbohydrate per day, I was quite resistant to them (i.e., I was very insulin sensitive) and remained exceptionally lean.

Fast forward to three years ago, at the age of 36, I weighed 200 pounds, had 25% body fat, a 36-inch waist and a 44-inch chest.  What changed over 20 years?  I was actually eating considerably less – in both absolute amounts and total carbohydrates – and yes, I was exercising a bit less (3 to 4 hours per day at 36 versus 6 hours per day when I was 16). But, is that the only thing that changed?  What changed in me, and what changes in most people over the same period of their lives, is that I became progressively more insulin resistant.  Most people casually observe that their “metabolism slows down” as they age, but what really happens?

I wish I could definitively tell you why this happens. I can’t. What I can tell you is how it happens. There are many factors, and they certainly vary by person and by individual significance.  The list below is a bit simplified and by no means complete.

1. Over time, endogenous production of sex hormones (e.g., testosterone, estrogen) becomes altered, and this seems to play a role in fat metabolism.  In addition to sex hormones, other non-sex steroid hormones (e.g., cortisol), which have a strong effect on fat metabolism, may be altered for a variety of reasons including sleep reduction and stress.
2. Perhaps (at least partially) related to this, the cellular distribution and density of lipoprotein lipase (LPL) also changes.  [Recall, LPL is a very important enzyme on the surface of muscle cells and fat cells.  On muscle cells, it fosters fat oxidation (good). On fat cells, it fosters fat accumulation (bad).]  As we age, we tend to have less LPL on muscle cells and more LPL on fat cells, both of which contribution to fat accumulation rather than fat oxidation.
3. The membranes of our cells tend to change in fatty acid composition, which may result in more difficulty getting the GLUT-4 transporter into cell membranes to foster glucose flux into cells.  I describe this process in this video.  The more difficult it is to get glucose into cells, the more insulin the pancreas must secrete to exert its eventual effect, the more exposure all cells have to circulating insulin levels.  Higher levels of insulin also exacerbate the phenomenon of more LPL on fat cells and reduced fat oxidation.

These changes are all linked, and probably play a different role of importance in different people at different times in our lives.

So what do gravity and insulin have in common?

The forces of gravity and effects of insulin are natural phenomena.  Sure, the comparison is not perfect, but it serves a very important purpose in making the following case:

1. These forces act on us whether we know it or not and whether we like it or not.
2. The net impact of these forces on you is highly dependent on your genes, your age, and the choices you make (e.g., practicing gymnastics versus siting on the couch, changing your eating habits versus eating the same old standard foods).
3. Just because some people seem to “defy” these forces does not negate their existence.  Michael Jordan dunking from the top of the free throw line doesn’t mean I can and doesn’t mean gravity is irrelevant.
4. What matters most is how these forces act on you. Be less concerned with the folks who lie to either side of you on the population distribution curve (i.e., those more or less impacted by gravity or insulin).  Figure out what works for you and be ready to modify the plan over time, because it will likely get less and less easy to maintain and improve your performance over time.  We may not be able to outrun Father Time, but we can keep him at bay.

Back to the topic of the week: What do anabolic steroids, EPO, and carbohydrates have in common?  I know what you’re thinking…what is he talking about?  I’m going to attempt to make the following case today: carbohydrates do, in fact, enhance some aspects of human athletic performance.  So do anabolic steroids, human growth hormone (HGH), synthetic erythropoietin (EPO), and countless other drugs classified loosely and broadly as “performance enhancing drugs.”  The question is, or at least should be, Is it worth using these substances to enhance your athletic performance?

Before we go any further, though, I want to ask you to suspend one thought – ignore the “legality” of these substances.  For example, if we were going to have a discussion about cigarettes and marijuana, I would ask that we have the discussion based solely on their pharmacologic, physiologic, and pathologic features.  The legal issue is actually arbitrary and, frankly, highly illogical at times.  So, let’s take legality off the table.  Carbohydrates are legal and anabolic steroids are not.  Cigarettes and alcohol are legal and marijuana is not.  Understood, but irrelevant for this discussion.

Many people question the logic of reducing or outright eliminating carbohydrates, given the possible reduction in athletic and physical performance.  I’ve written about the impact nutritional ketosis has had on my physical performance several times, including here, here, and here.

For those of you not familiar with “standard” performance enhancing drugs, let me digress momentarily to explain what they are, how they enhance performance, and their associated risks (besides being stripped of medals or going to jail).

Anabolic steroids

This class of drugs, broadly speaking, includes a group of molecules that mimic the male sex hormones testosterone and dihydrotestosterone (DHT).  There is a reason, on average, that men have more strength and muscle mass than women, and these hormones play the predominant role in causing this difference.   Exogenous (i.e., supplementing whatever amounts the body naturally produces) use of these synthesized molecules leads to an increase in muscular strength and size when an individual – male or female – combines their use with suitable training.  In other words, taking anabolic steroids and playing video games does not increase your ability to run faster or lift more weight.  You still have to train hard.  However, anabolic steroids provide at least three significant advantages over doing it the “old fashioned way.”

1. Using anabolic steroids allows you to recover much quicker, and therefore facilitates your ability to train harder than someone not using them.  The mechanism of this action is probably related to their ability to block inflammatory processes in your body.  Ever wonder why you hurt so much after a tough workout (or a long flight)?  Part of it is muscle tearing, which I’ll address in the next point.  Part of it, though, is your own immune system kicking up a fuss via an inflammatory cascade in an attempt to i) prevent you from causing more harm, and ii) repair the damage.  Blocking this process lets you feel better and workout longer and harder.
2. Through their ability to directly signal at the level of the cell nucleus (steroid hormones go right into the cell nucleus and interact directly with DNA), anabolic steroids also directly increase protein assimilation into muscle tissue.  In other words, they increase anabolism – muscle building.
3. Finally, anabolic steroids have been shown to decrease lipoprotein lipase (LPL) expression on adipose cells [Translation: anabolic steroids reduce the expression of an enzyme that sits on fat cells and “tells” them to store more fat].  Less LPL on fat cells = less body fat.

Taken together, these physiologic changes make you a leaner, more muscular, stronger person.

So what’s the catch? There is an enormous, and very contentious, body of work around the question of chronic toxicity associated with use of anabolic steroids.  I am not an expert in this, and I won’t pretend to be one.  I have read about it quite a bit and my take is that this field of study is shockingly parallel to that of nutrition, except with smaller sample sizes, worse science (if that’s possible), and even more involvement from Congress (it’s almost embarrassing how much Congress obsesses over this topic with public hearings relative to other problems in our society…but I digress).  If you want to see a fantastic (and highly factual) documentary on this topic, I’d recommend Bigger, Stronger, Faster*.

Chronic use of anabolic steroids is certainly associated with some undesirable consequences, such as increased blood pressure, dyslipidemia (especially reduced HDL-C concentration), acne, premature balding, erectile dysfunction, infertility, clitoral enlargement in women, and gynecomastia in men.

There is a lot of controversy around the psychiatric side-effects of anabolic steroids, especially with respect to depression leading to suicide and a condition commonly referred to as “roid rage.” Most data I have seen suggest anabolic steroids may amplify an already-existing condition but are unlikely to cause these symptoms.  Nevertheless, the side effects of using anabolic steroids are not negligible.

Anabolic steroids unquestionably enhance an athlete’s ability to do virtually anything that requires strength.  I can’t think of a sport where the use of anabolic steroids is not associated with a significant improvement in performance.  But this improvement comes at a cost.  The cost is, for most, dose-dependent (i.e., more use = more chance of side-effects), and certainly not always predictable.

EPO

Erythropoietin (EPO) is a hormone produced by the kidney which regulates the body’s production of red blood cells – the cells in our bloodstream that transport oxygen to all tissues and carbon dioxide back to the lungs.  Under normal circumstances the body highly regulates the concentration of red blood cells and hemoglobin. Hemoglobin is the protein carried by the red blood cells that actually binds oxygen and carbon dioxide and allows red blood cells to transport these gases in our bloodstream.  If you donate blood, for example, you are “giving away” red blood cells and hemoglobin.  Your kidneys, sensing this, make more EPO, which signals to your bone marrow to make more red blood cells and hemoglobin.

Blood doping, a practice carried out by athletes at a higher frequency until the development of synthetic (i.e., artificially produced) EPO, is the “messy” way of doing this.  An athlete would have about 10% of their blood drawn and stored a few months before competition.  In the ensuing period of time, their body would naturally produce EPO and return the hemoglobin level to normal.  Just prior to competition the athlete would re-inject their own previously removed red blood cells, giving them supra-normal levels of hemoglobin.  Today, synthetic administration of EPO gives the same result with less hassle.  There are subtle differences between these techniques, including how they are each detected in screening for the drug.

What are the benefits of using EPO?

If the average person walks around with a hemoglobin concentration of 13 to 15 g/dL, boosting that to, say, 17 or 18 g/dL provides a significant advantage in delivering oxygen to muscle cells and clearing carbon dioxide back to the lungs.  Any athlete whose performance is limited by oxygen carrying capacity (e.g., running, cycling, swimming, tennis, triathlon) will experience a great performance advantage using EPO.

The catch? There’s probably a teleological reason our bodies have evolved to regulate hemoglobin levels between about 13 and 15 g/dL.  Anything lower than that and we have less energy and deliver less oxygen to our muscles (though many people do live below this concentration).  But in a very non-linear way, as the concentration of hemoglobin rises above about 15 g/dL (which can occur naturally in a few disease states), the viscosity of blood increases, which directly increases the likelihood of blood clot formation.  In particular, increased blood viscosity is associated with an increased risk of myocardial infarction (heart attack), cerebrovascular thrombosis (stroke), and pulmonary embolism (blood clots in the lungs).  All of these conditions, obviously, can be fatal. While it’s unclear what percent of athletes who use EPO or blood dope suffer these adverse effects, it’s not zero.

Carbohydrates

Carbohydrates are one of the three macronutrients we consume (the others being protein and fat).  What makes carbohydrates unique is that our bodies can use them under anaerobic conditions.  This means that at levels of exertion so great that your body cannot get oxygen to cells quickly enough for oxidation (use of oxygen to fully harness the energy of fat or carbohydrate), you can still use a less efficient method to extract some energy.  For a quick refresher on this concept, refer back to this post.

It’s a bit more complicated, though.  You’ll recall from this post and this post, one can still carry out anaerobic activity without actually eating carbohydrates.  How? The quick answer is that consuming protein and fat, even without carbohydrates, generates sufficient substrate to produce glycogen, which is actually what our muscles use during these periods of cellular oxygen deprivation.  Do our muscles and liver contain as much glycogen without consuming carbohydrates?   Almost certainly not.  Are our muscles as efficient at utilizing glycogen in the absence of regular carbohydrate consumption?  Not in my experience.  In other words, eliminating carbohydrates from your diet can be detrimental to some aspects of your performance.  Stated yet another way, carbohydrates are a performance enhancing substance. 

I’m not going to spend any time discussing the “catch” (i.e., the drawback) with respect to carbohydrate consumption (e.g., insulin resistance, metabolic syndrome, obesity, diabetes, cancer, Alzheimer’s disease) since I devote this entire blog to that topic, so let’s revisit the original question.

What do anabolic steroids, EPO, and carbohydrates have in common?

For starters, they all enhance some aspect of your athletic and physical performance, depending on the activity you’re participating in.  Secondly, they all have variable efficacy depending on dosage and genetic/individual factors.  Finally, they all have side-effects, also dependent on dosage and genetic/individual factors.

Is it worth using performance enhancers?

Keeping legality out the discussion, (after all most of us are not Olympians subject to constant drug testing and regulations), should we use anabolic steroids, EPO, or carbohydrates to enhance our physical performance?

It depends.  Again, let’s keep legality out of it to normalize the discussion.  If your goal is to win the Tour de France, should you use EPO and some form of anabolic steroids?  It’s very hard to imagine how anyone, regardless of natural ability and training, could do what is expected of these athletes without some supplemental chemistry.

What if you want to be a starter in the NFL? Hit more home runs than anyone else? Set the world record in the 100-meter dash? I’m not saying you must use performance enhancing drugs to do these things, but it sure helps.  Furthermore, if anabolic steroids, EPO, and other performance enhancing drugs weren’t actually illegal, I’d be willing to bet their use would increase dramatically among both professionals and non-professionals.  [Non-professionals – i.e., “normal” folks like you and me – far outnumber professionals in the use of performance enhancing drugs, probably by over 10 to 1.]

I will pass no judgment on anyone who chooses to use anabolic steroids or EPO or carbohydrates to enhance their performance.  I will also pass no judgment on folks who use marijuana to ease their pain or to relax.   As I said earlier, I think the legality of these substances is arbitrary.  Cigarettes and alcohol are ok, but marijuana and anabolic steroids are not?

Everything has a tradeoff, which is exactly why I don’t like being asked, “Hey Doc, what should I be eating?”  How should I know?  It’s as illogical a question as, “Hey Doc, should I be using anabolic steroids?” If you are aspiring to win an Olympic medal (again, assuming all performance enhancers were legal), the answer is probably, “Of course you should…and while you’re at it, add some human growth hormone!”

You want to win the NCAA championship in the 200 yard freestyle?  Ketosis is probably not for you.  Sure you can (and should!) restrict sugar, but I think you’d be better off consuming, say, 40% of your calories from rice and non-wheat, non-sugar starches.

So why am I in ketosis, even though I might “perform” better at some things if I ate carbohydrates?  Because I’m a 39-year-old wannabe athlete whose athletic performance is irrelevant.  Not a single person cares how fast I swim or ride my bike beyond myself.  I have no sponsors. I will never earn a paycheck for how fast I can flip tires or climb Mount Palomar.  I am more than willing to give up some athletic performance (e.g., sprint speed, peak power) in exchange for other athletic benefits (e.g., greater aerobic capacity and metabolic flexibility), especially when the real gain is greater health and a reduction in my risk for all diseases associated with metabolic syndrome (heart disease, diabetes, cancer, Alzheimer’s disease, and others).

Can I tell you what to eat, what to drink, what to smoke, or what to inject?  Perhaps, though I’m not sure how relevant it would be (or why you’d want to listen to me).  What I really want to do is at least give you a sense of how to think about the tradeoffs involved in each of these decisions so you are better able to make the right decision for yourself about what to inject or what to eat to enhance your performance.

Remember, I was one of those doctors in the mainstream once upon a time.  While I always tried (and hopefully succeeded most of the time) to treat overweight patients with respect, I silently judged them.  Why can’t you just eat less and exercise more?  Only when I realized, despite my diet which rigorously adhered to formal recommendations and my 3 to 4 hours of exercise per day, that even I was getting too fat for comfort, did I begin to question the Conventional Wisdom of why we get fat.  Of course, not everyone (fortunately) was born with my level of genetic susceptibility to insulin resistance (stated another way, not everyone is born with my level of carbohydrate sensitivity).  In my experience, about 10-20% of the population (my lucky wife included) seem resistant to carbohydrates and maintain exquisite insulin sensitivity, almost independent of diet.   Roughly 30-40% of the population are, conversely, very sensitive to carbohydrates and appear to be quite insulin resistant until nearly the last gram of sugar and most carbohydrates are removed from their diets.  Then there is the rest of population, which includes me.  To varying degrees, we’re somewhere between these two groups.

So back to this question — If carbohydrate reduction is so effective for weight loss, why are so many people still overweight?  Beyond being asked this question, personally (and frequently), one can see the same logic in the academic literature (see comment by George Bray in Obesity Reviews) and in the press (see comment by Gina Kolata in the New York Times).

George Bray: “I thus conclude that if any diet ‘cured’ obesity as their proponents often claim, there would be no obesity and thus no need for the next diet.  Yet the past 150 years, since the publication of Banting’s first popular diet*, have seen a continuing stream of new diet books.”

Gina Kolata: “Low-carbohydrate diets have been popularized periodically since the 19th century. Best-selling book after best-selling book promoted them. Yet if they work so well, why are so many people still searching for an effective way to lose weight?”

*If you have not yet done so, and you’d like to put yourself in the ‘low-carb aficionado’ club, you must spend time reading the work of Banting.

Dr. Bray is generally regarded as one of the most erudite authorities on obesity in the United States, while Ms. Kolata is one of the leading reporters on the topic – so we’re not just talking about “anyone” asking such questions.  Bray and Kolata are both smart and thoughtful people who have devoted much of their lives to thinking about this problem. In other words, we’re actually all on the same “team” – we desperately want to help people lead more fulfilling, healthy lives by improving their eating habits.  But we disagree on this point.

It seems Dr. Bray and Ms. Kolata (and many others) have proposed an interesting Principle, below:

If a disease is prevalent, no treatment exists to eradicate it. In other words, if any condition exists, it implies there is no cure for that condition.  The reverse (and logically equivalent) statement is this: if a treatment exists for a disease, no one has the disease.

Is this a valid criticism of carbohydrate restriction?  Perhaps, but to be sure let’s consider a few examples of this Principle.

• Polio no longer exists in the United States, thanks to the development of two types of vaccines to immunize people against the poliovirus.
• Smallpox, a viral disease estimated to have taken between 300 and 500 million human lives in total, no longer exists thanks to two vaccines that eradicated the disease in 1979.
• Breast cancer still exists, and in 2011 claimed the lives of 40,000 women in the United States alone. While there are many treatments for breast cancer (surgery, radiation, chemotherapy, and combinations of these) depending on stage of disease, no cure exists to eradicate it once it is systemic (i.e., spread throughout the body), which is consistent with the Principle. [Remember “logic 101” tells us that if A implies B, no-B implies no-A.]

So far the Principle seems pretty compelling.  Of course, to be an all-singing-all-dancing-universal-truth, there cannot be any exceptions to this Principle.  Do any such exceptions exist?

• HIV, when progressed to AIDS, is responsible for nearly 2 million annual deaths worldwide (about 16,000 deaths per year in the United States), yet transmission of the HIV virus – the causative agent – is entirely preventable.  Furthermore, the current drug regimen for HIV can prevent nearly all patients with HIV from progressing to AIDS, thereby rendering HIV a chronic disease.
• Malaria, a disease transmitted by mosquitoes, is responsible for about 1 million deaths worldwide each year, yet this disease can be prevented successfully via two broad strategies: prophylactic treatment with anti-malarial agents (this is typically what folks do when traveling to regions where malaria is prevalent) and use of anti-mosquito “technology” (e.g., nets, DEET).  Furthermore, when a person, despite these measures, contracts malaria, prompt treatment with anti-malarial drugs will cure most.
• Polio, which has been eradicated in the Western world, is still prevalent in south Asia despite a clear method of prevention.

For the purpose of space and time I’ll stop here with examples, but it turns out there are far more examples of the Principle being violated than being upheld.  In other words, the Principle isn’t actually a Principle.  It’s an idea that is true less often than it is false.  Sort of like the idea dogs and children should never be together (which I used to believe after many years of suturing up the faces of children who had been ravaged by dogs).  I now realize that most children around most dogs are perfectly safe, and adult supervision can make the odds even better.

What is the common theme in each of these examples that defy the Principle?

It’s probably a combination of factors, and they differ across the examples, too. Let me use HIV as an example of this phenomenon.  I did my residency in general surgery at the Johns Hopkins hospital in Baltimore, Maryland.  For those of you not familiar with Baltimore, some background is warranted.  In the final weeks of medical school I took the advice of a friend and read the book, The Corner, by David Simon and Ed Burns.  This riveting true story was the single most valuable book I could have read prior to moving from posh Palo Alto to inner city Baltimore.  Through this book, other books, and eventually my own personal experience, I came to realize how Baltimore had become the heroin capital of the United States.  Furthermore, because of where Hopkins is situated in the city, I would come to spend many years taking care of patients in the emergency room and hospital wards who battled heroin addiction.

As a result of such high rates of heroin addiction, the number of patients walking (or being carried into) the Hopkins ER was very high.  If I recall correctly, and these numbers do change over time, approximately 60% of patients walking (or being carried) into the Hopkins ER were positive for HIV, hepatitis B, and/or hepatitis C.  Each of these diseases is transmitted through blood or other bodily fluids.   Needle sharing and sexual transmission are far and away the most common modes of transmission in the United States today.

Preventing HIV, hepatitis C, and hepatitis B is pretty straight forward today.  If you have sex, especially with “high risk” individuals, do so with a condom.  If you use IV drugs, do not share needles.  One could even go a step further and not use IV drugs at all and not have sex with high-risk individuals (e.g., prostitutes).  [Hepatitis B, while 10x more transmissible than hepatitis C and 100x more transmissible than HIV is the only one of these three viruses for which there currently exists a vaccine.]  While there are other ways these three viruses can get transmitted, practically all (>99% as of 2007) are contracted through these two routes of transmission in the United States.

Furthermore, the treatment for HIV using a treatment regimen called HAART (Highly Active Anti-Retroviral Therapy) has become highly efficacious at preventing HIV from even progressing to AIDS.   In other words, if one contracts HIV today, it’s quite likely to prevent HIV from progressing to AIDS.

How can it be possible, you ask, that anyone can contract a disease that is so easily preventable? Furthermore, for those who have contracted the disease, how can so many go without treatments that would easily render their condition a chronic one – a condition that will not lead directly to their death — rather than a condition that will lead to their death?

Information, infrastructure, and pain

One could (and I’m sure several have already done so) write an entire dissertation on this exact topic.  At the risk of oversimplifying, though, let me briefly explain why I believe a disease that has a preventable cause and effect can still exist.  There are three broad reasons, though they are not all equally contributory nor are they constant for all people (i.e., the dominant reason for one person might be less relevant for another person).

Poor information

While it might be “obvious” to many of us, it’s actually not clear to everyone that a virus can cause a disease like AIDS.  Heck, most folks don’t actually know what a virus even is.  Furthermore, some people do not know how the virus is transmitted or how, exactly, to prevent this transmission.

In the United States today, the group of people who contract HIV primarily because of what I call “poor information” is probably quite low. But in Africa, for example, this probably plays a significant role in transmission.

Poor infrastructure

Even if one realizes how the HIV virus gets transmitted and what the consequences are (i.e., “poor information” is not an issue), another feature – poor infrastructure – can play a role in facilitating spread of the disease.  While condoms and clean needles can greatly reduce the transmission of HIV, accessing them is not always easy, especially if one is on a tight budget, as many folks addicted to heroin are.   And while programs exist to literally give away needles and condoms, not everyone can access them in a time of need.

Pain versus consequence

Why do people use HIV infected needles when they can find clean needles at a shelter?  Why do people have sex with prostitutes without using condoms, even though they can access condoms for free?  I don’t think there is one clear reason or explanation.  Some of it is social support and surroundings.  Some of it is prioritization.  Some of it is pain.  Perhaps the pain transiently ameliorated by heroin or sex is deeper than the long-term cost?

What have we learned?

1. A disease can exist despite a means of prevention.
2. A disease can exist despite an effective treatment.
3. The barriers to prevention and treatment are likely multi-faceted and complex (and highly dependent on the disease).

While I’ve only used HIV (and by extension, hepatitis C and hepatitis B) to illustrate this point, I hope I’ve given you some idea how someone can still “get” a disease, while living in the United States circa 2012, despite all of the good information and infrastructure to prevent it.

As you undoubtedly know, the problem is far worse outside of the United States.  In many parts for the world the people being afflicted with HIV lack even the correct information, let alone a shred of infrastructure to combat the problem.

Back to the original question

How does obesity stack up?  Let’s evaluate using this framework.

Information

Unlike HIV which, at least in the United States, is appropriately understood, the study of nutrition and obesity is a relative debacle.  The formal recommendation of the USDA, AHA, AMA, ADA, and others actually tell us to eat the foods that make approximately two-thirds of us overweight.

Try asking your doctor for help, and you’re likely told to eat less food, eat less fat, eat more grains, and exercise more, stupid.

Infrastructure

Since approximately 1972, U.S. food policy has almost monotonically been shifting further and further towards all but making it impossible to avoid carbohydrates.  Countless books have been written about this topic from many levels from agricultural subsidies to the lobbying powers of those who sell sugar.

The results of these actions are particularly devastating on those individuals who are not affluent.  If you wonder why the economically disadvantaged are more likely to be obese, ponder this:  one can buy ten boxes of ramen noodles for one dollar at most grocery stores.  On a per calorie basis, few things are cheaper than sugar and other carbohydrates.

If you’re hungry in an airport or a mall (or virtually anywhere out of your own home), how easy is it to avoid sugars and simple carbohydrates?

Pain

Like Dr. Rob Lustig has said on many occasions, I don’t believe anyone chooses to be overweight.  I do believe most people who are overweight are so because of poor information and poor infrastructure.  However, these two features are not the only reason.  Many people still smoke cigarettes today in the United States, despite good information (i.e., everyone “knows” smoking is harmful) and good infrastructure (e.g., cigarettes are very expensive and most places don’t allow smoking – the default action is not to smoke).  There’s another reason people smoke.  Similarly, some people will always turn to the wrong foods.  I guess, for some, the acute pleasure food brings outweighs the chronic pain it causes, even when information about food is clear and unambiguous and when infrastructure does not essentially force people to eat the wrong foods.

I don’t know how much of a role this feature will play when the former two features are one day corrected, but I’m sure fixing the former two will go a long way to reversing the epidemic we find ourselves living and dying in.

Should we be surprised that 67% of Americans are overweight and that nearly 10% have diabetes?

We are outright told to eat the foods that make us fat via all formal and informal recommendations. We are surrounded by food infrastructure that makes our “default” eating patterns in line with those (flawed) recommendations. And for those of us who decide to go against the grain and overcome these two enormous hurdles, we are almost assuredly not supported.  In fact, we’re often condemned and ridiculed.

To Dr. Bray and Ms. Kolata:  While I respect your commitment to fighting obesity, diabetes, and their associated chronic diseases, I reject your reasoning for why reducing carbohydrates is not one of the most effective treatments.

p.s., when I wonder if my blog has any impact on people, I only need to see a picture like this one (from a loyal fan) to know I’m having some impact! [If you don't "get" it, check the video from this post a while back.]