The world has more fat people today than any other time in history and the number is increasing.

Worldwide obesity has more than doubled since 1980. There are over 1.5 billion adults who are overweight. Of these over 200 million men and nearly 300 million women are obese. Approximately 43 million of children under age of 5 are obese.

Overweight adults and children are traumatised as the society stigmatizes them as chubby, plump and fat.

The media’s emphasis on skinny models, TV presenters, and celebrities does not help the situation because this implies that plus-size people are to blame for their plight.

But,  what causes obesity?

The fundamental cause of obesity and overweight is an energy imbalance between energy consumed and energy expended.

The two blamed causes are; an increased intake of energy-dense foods that are high in fat, and sugars but low in vitamins, minerals and other micronutrients; and a decrease in physical activity due to the increasingly sedentary nature of modern lifestyle.

However I feel that some overweight people are unfairly blamed for being lazy, not exercising enough and eating junk food. There are other reasons for adding weight which are beyond their control.

What is Obesity and overweight?

Before exploring other factors that cause increase in body mass, let us look at what are overweight and obesity and their unwanted effects.

According to World Health Organisation (WHO), ‘Overweight and obesity are abnormal or excessive fat accumulation that may impair health’.

Body mass index (BMI) is the simplest parameter that is used to measure overweight and obesity in adults.

BMI is defined as a person’s weight in kilograms (kg) divided by the square of height in meters (m). Therefore the units for BMI are kg/m².

Generally, a BMI greater than or equal to 25 is overweight while a BMI greater than or equal to 30 is obesity. These values should be considered as a rough guide as there are different levels of fatness.

Why is overweight and obesity bad?

High BMI is a major risk factor for several modern diseases such as cardiovascular diseases (mainly heart disease and stroke), diabetes and some cancers (endometrial, breast, and colon).

Overweight and obesity are the fifth leading risk for deaths globally. At least 2.8 million adults die each year as a result of being overweight or obese.

The ‘Big two’

The energy imbalance that is blamed for obesity is based on the first law of thermodynamics.

The first law of thermodynamics, popularly known as law of conservation of energy states that ‘energy can neither be created nor destroyed, but can be transformed from one form to another’.

According to this law, if you drink half litre of beer, the body has two options. The first option is either to use all of it or pass all of it out. The second option is pass some quantity and the remainder is used by the body. All foods follow the same chain, a portion is used in the body, and another share is converted into fat or expelled.

The law of conservation of energy dictates that the energy equation has to balance; the energy consumed in form of food has to be equal to what is used up in the body plus the expelled waste.

According to the law of energy, the weight gain is only blamed on the ‘big two’. Firstly, eating excess calories and secondly lack of physical exercise to convert the excess calories into some other form of energy.

Ideally men should take approximately 2500 Kilocalories while women take 2000 Kilocalories per day. Excess calories above these quantities has to be expelled, otherwise they will be deposited as fat and manifest as overweight.

However the first law of thermodynamics does not tell us how other factors in the body such as gene, gender, age, and ethnicity affect the energy balance equation.

For example, law of energy does not tell us why women deposit fat in different parts of the body from men.

Also, this law is numb on why some ethnic groups such as those with Indians ancestry tend to be prone to weight problems than others.

The energy balance school of thought ignores many other factors which could also be responsible for increasing waste lines.

No doubt that excess calories and lack of physical exercise are the salient factors that contribute to human weight gain. However, the evidence to their contributory role is circumstantial.

For example, those two factors cannot also explain why those who take psychotropic medications such as antidepressants and mood stabilizers or even steroid hormones and contraceptives gain weight. This is despite the fact that most of these medications are calorie free.

Majority of those who follow regular exercise and control calorie intake lose weight. However, others watch their calories and engage in physical exercise, but feel helpless and sometimes guilty when they find themselves piling on kilos.

The  less traveled road

There must be other factors that contribute to this quandary of weight gain than just excess calories and reduced physical exercise.

Let us take the less travelled road and look at some unacknowledged factors that are leading to increased population of overweight people world wide.

The evidence among these factors could also be circumstantial but there is strong scientific evidence to link them to overall increase in weight gain around the world overtime.

1. Maternal age

Surprisingly, a risk factor to obesity is having an elderly mother.

Generally, the age of mothers before having the first baby is increasing globally. This is necessitated by need to advance in education and career before taking up the role of motherhood.

In early 70s and 80s most women became first time mothers at early 20s. Now that age is increasing and majority are not having babies until late 30s.

Babies born by mothers at such advanced ages are at higher risk of becoming obese.

In Britain, a study of girls aged 9-10 years old found that odds of obesity increased by 14 percent for every 5 year increment in their mother’s age.

2. Body weight associated with greater reproductive fitness

According to natural selection, physically endowed women are associated with fertility and health-child bearing. Consequently, the number of offsprings is directly related to body weight in women.

BMI (or adiposity) has a heritable component of approximately 65% which is well supported by studies. This suggests that obese mothers can pass overweight genes to their children leading to a higher population of overweight people.

It is also true that leanness to certain point impairs women fertility. This limits their ability to bear children and transfer genes of fineness.

Read the other factors in the next article.

I wrote this article for Kenya’s leading newspaper, Daily Nation on 8th November 2011. You can read it online here. 

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By following simple guidelines when storing food in the refrigerator it can help food to store longer and minimise risks of cross-contamination.

It is safe to store all non dripping foods such as packaged milk, cheese and similar products on the top shelf.

Store cooked salads below cooked meat in the middle shelves but always above raw meat and chicken. This reduces chances of drip (juices) from raw meat contaminating the salads. The juices from raw meat are blood and water, but they are normally loaded with some bacteria. Salads are never cooked, therefore, if contaminated they pose a serious health risk.

Salads should always be covered or wrapped with cling film to minimize any chance of contamination and should be washed thoroughly before use.

Uncooked meat and sausages must be stored at the bottom of the fridge and above raw chicken but not the other way round. This is because chicken are normally prone to higher level of bacterial contamination than meat.

Store leafy vegetables such as kales (sukumawiki), cabbages, celery, broccoli in the crisper which is usually at the lowest shelf in the fridge. Crispers are designed to control the amount of humidity for maximum storage of vegetables and fruits.

Effects of power failure to refrigerated food

The refrigerator with food should always be powered on. In case there is a breakdown or prolonged power failure, all the food should be consumed within the shortest time possible. Absence of power to the refrigerator means that the temperature of the food goes up and reaches danger zone (10 – 40 °C).

Danger zone temperatures create conducive environment for the bacteria to reproduce, multiply and grow causing food spoilage or poisoning.

It is an extreme health risk to switch off refrigerator loaded with food at night or any other time to save power. This is because bacteria can grow in the food posing a health risk. Switching off empty refrigerator to save power is a good practice though.

Which foods freeze well?

Most meat products freeze well including beef, pork, chicken, sea foods, some fruits, bread and pastry products.

Before freezing, these products should be packaged in water tight wraps or freezer bags. Otherwise they will lose their texture and quality following removal from the freezer and defrosting.

Which foods should not be frozen?

Never freeze eggs in the shell or they will burst. However, cooked eggs can be frozen.

Also never freeze any canned foods although the canned products can be emptied and frozen.

Mayonnaise and milk should not be frozen as they sometimes curdle.

Fruits and vegetables that contain high water content do not freeze well, and the change in their texture is extremely noticeable on thawing. Examples include lettuce, celery, radishes, strawberries, melon, cucumber, spinach and cabbage. These foods are not usually frozen at all.

Strawberries can be frozen if they will be used in frozen state. This is common in making smoothies.

Is frozen food safe?

Frozen food is safe for human consumption. Freezing puts germs and enzymes that spoil food into dormancy but does not kill them. Once frozen foods are thawed the germs become alive again and multiply spoiling the food or even causing illness.

Why does frozen food develop black marks?

The discoloured spots or marks on frozen food are as a result of freeze injury or freeze burn.

Freezer burns are some greyish-brown spots on frozen foods such as meat or vegetables. Freezer burn is caused by air coming in contact with the surface of the food. They are merely dry spots and they do not render food unsafe.

Cut freezer-burned portions away either before or after cooking the food.

Freezer burns can be prevented by three ways, either by wrapping foods tightly before freezing, ensuring temperature in the freezer does not go above zero or avoiding storing foods for very long periods.

What should you do if power to the freezer fails?

For some unknown or known reason, there could be power black-out or power failure to the freezer. The first thing to do is keep the door closed. If the door is ajar the food will thaw faster and go bad. If the freezer is full, it can keep food for up to 2 days. However, if it is half-full, food will store for shorter periods. Regroup foods together, especially put meat and poultry products together so that their juice does not contaminate other foods until the power is fixed. Avoid consuming food that has reached room temperatures in a broken freezer.

Which are the best and safest methods for defrosting foods?

Let’s say you have some frozen meat that you want to cook. One of the simplest ways is to cook it directly from the frozen state. This is safe but takes longer time, approximately double the time required to cook unfrozen meat.

Certain foods such as frozen oven chips are supposed to be baked direct from the frozen state.

Other foods require defrosting or thawing before cooking, which is the process of converting ice in the frozen food to water. Safe methods for defrosting frozen foods are;

Defrosting in the refrigerator

This is most recommended defrosting method because at refrigeration temperatures, the possibility of bacteria to reproduce and multiply is reduced. Defrosting in the refrigerator, however, requires considerable amount of time, it might require up to a whole day to defrost half kilogram of beef or chicken.

Foods defrosted in the refrigerators such as poultry, stew meat and minced beef can remain safe for one more day before cooking. Red meat such as steaks and pork chops can remain safe for 2-3 days before cooking.

Foods defrosted in the fridge can be refrozen again immediately if they have not been exposed to room temperature.

Cold water defrosting

This method of defrosting is quicker than in the refrigerator but requires extra care. Food has to be put in water-impermeable and leak-proof packages otherwise the food can get watery or contaminated from the water and atmosphere.

Submerge leak proof plastic bag with food in cold tap water and keep changing the water every half an hour.

Foods defrosted by water should be cooked immediately and if they have to be refrozen, they should be cooked first.

Defrosting half kilo of meat with cold water can take about 1 hour or less.

Defrosting in the microwave

This is the fastest method of thawing food but be prepared to cook the defrosted food immediately. Most of the microwaves come with a defrosting option for different foods on the control panel.

Once food is defrosted in a microwave, it should be cooked immediately since some sections might have reached what is called danger zone temperatures that are favourable for multiplication and growth of bacteria.

Microwave defrosted food should never be refrigerated or refrozen unless after cooking.

Recommended storage times for common foods

Uncooked steaks, pork chops, whole chicken or pieces can store for 3-5 days in the fridge. However minced and diced cubes of meat should not be stored for more than 2 days. Fish can keep for 1-2 days, while packet milk can keep for up to 5 days after opening. It should be noted that fresh milk obtained directly from the cow will keep for shorter period of time if not boiled (pasteurized). Cooked meat and chicken can keep for 3 – 4 days. Steaks and chicken can be frozen for 6-12 months.

Tips to safe storage of foods in the fridge

1. Maximum hygiene of the food products and the refrigerator should be observed. Refrigerator does not kill germs!
2. Refrigerate and freeze foods immediately to minimize risks of microbial growth and multiplication.
3. Keep raw meat away from other foods to avoid cross-contamination.
4. Never switch off fridge loaded with food to save power. This may pose a serious health risk. In case of power failure, the food can keep for up to six hours. If more than that, consume the food within the shortest time possible.
5. Foods does not store forever in the fridge. Store food for the recommended time only. Food spoils after a given period of time.

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Food refrigeration and freezing are the modern methods of choice for preserving food. Most often refrigeration has positive results; the food keeps safe for long, nevertheless, sometimes the unexpected happens. For example, refrigerated bananas and a variety of vegetables develop black marks; tomatoes turn soggy, frozen meat turn brown and even some foods go bad.

These unexpected changes invite a flurry of questions such as: is refrigerated and frozen food safe? Why do some foods go bad instead of keeping longer in the fridge? Which foods should/should not be refrigerated and which should be frozen? Does refrigeration kill nutrients? Welcome to the answers to these and other burning questions about food refrigerators and freezers.

Why do foods go bad?

Food go bad because micro-sized unwanted animals called bacteria breed, multiply and grow in it. Not all bacteria cause food to go stale and some are even beneficial. The specific group of bacteria that spoil food are called spoilage (from the word spoil) bacteria.

Stale food is recognized either by bad smell, unusual colour, bad taste or slimy texture which render it unpalatable. These undesirable sensorial properties originate from waste matter expelled by the bacteria.

There is another category of relatively more harmful bacteria that can grow in food but rarely cause any undesirable flavour or discolouration. These bacteria are called pathogenic (from the word pathogen) bacteria. They either release poisonous chemicals into the food or they grow into large numbers that are toxic.

Although food contaminated by pathogenic bacteria does not show any sensorial noticeable changes, if consumed, it causes food borne illness which is usually referred to as food poisoning.

How does refrigeration preserve food?

Spoilage bacteria thrive well in high temperatures ranging from room temperature to 40 °C but, do poorly in cold temperatures.

Refrigeration provides low temperatures that slow reproduction, multiplication and growth of spoilage, pathogenic and poison producing bacteria.

Refrigeration does not kill the bacteria!

What is the origin of refrigeration and freezing?

The use of cold storage to preserve food dates back to pre-historic ages. Ancient man discovered that his hunted game meat could be stored in coolness of caves or covered with snow for the time of scarcity.

Before the first millennium, Chinese, Romans, Hebrews and Greek harvested ice and stored it in pits on the ground insulated with wood or straw for food preservation.

The first record of man who paved the way for modern refrigeration is William Cullen of Glasgow University, Scotland who produced cold by evaporating ether in 1748.

Jacob Perkins developed the first practical refrigerator machine in London in 1834 by using ether as a refrigerant.

In 1897, William Singer of New York patented the earliest automatic electric unit for small scale refrigeration.  From then on refrigeration evolved into what we have today, domestic, commercial and transport refrigeration systems.

How does refrigeration differ from freezing?

In refrigeration, food is stored between a temperature of 3-7 degrees Celsius which are slightly higher than the sub zero temperatures of the freezer.

Freezing causes the water in the food to turn into ice which is normally not the case with refrigeration. Therefore, frozen foods store longer (up to 6 months) compared to a maximum of 7 days in a fridge because freezing eliminates the free water available for bacterial growth, chemical and biochemical reactions.

How does the refrigerator work?

A refrigerator cools food and remains cool even under the blistering heat of Mombasa by employing two principles of gas laws. One is compressing air; the other is depressurizing the air. To do this, the refrigerator has a small unit called compressor at bottom rear that makes a refrigerator to hum so often.

Running from the compressor is a continuous loop of coils, one loop to the inside of the refrigerator, regarded as evaporator and the other to the outside (condenser). The coils to the inside are invisible while those to the outside are exposed.

Gas laws state that if you compress a gas into a small volume the temperature increases and when you expand a gas it temperatures drop. That is why when you pump a bicycle tyre, the tyre and the pump gets warm because you are trying to fit large amount of gas into a small volume.

On the other hand when you decompress a gas or spray an already pressurised gas such as deodorant you get a really cold sensation. This is because the released gas from deodorant nozzle expands and occupies a large volume, cooling down.

The refrigerator compressor pumps a type of special gas called refrigerant or coolant into the coil running to the inside of the refrigerator. As the coil enter the fridge the diameter gradually increases, the refrigerant passes through a valve, evaporates and expands dramatically cooling down. This is known as the Joule-Thomson (or Joule-Kelvin) effect after the physicists who discovered it, James Prescott Joule (1818–1889) and William Thomson (1824–1907).

The second law of thermodynamics states that when a substance at higher temperature is in contact with a cooler substance, the heat flows from the hotter material to the colder one. This is the magic the fridge uses to do the job, the heat from the food in the fridge moves to the colder refrigerant in the coils.

As the refrigerant is leaving the refrigerator it passes from wider tube to narrower rear coil (condenser), gets compressed and turns into liquid releasing the heat to the outside. That is why the rear of the refrigerator is normally warm.

The constant and continuous flow of the refrigerant picks up heat from the inside of the refrigerator and carries it to the outside like a heat conveyor belt. Voila, food is cooled.

Does refrigeration kill food nutrients?

Refrigeration does not kill nutrients. However some foods can change the colour, become soggy or develop dark marks. This is due to different injuries they suffer in the refrigerator but these does not in any way affect the nutrients unless food is stored for unsuitably long periods.

Why does pepper and tomatoes develop black marks in the fridge?

Some fruits and vegetables undergo chilling injury in the fridge. Signs of chilling injury include; surface lesions, discoloration and wilting. Fruits and vegetables susceptible to chilling injury which should not be refrigerated are apples, tomatoes, cucumber, oranges, pawpaw, pineapple, banana, mango, pepper and lemons.

Which food should be refrigerated?

The best guide on foods to be refrigerated is your local supermarket. Take note of foods that are stored at ambient temperature and those refrigerated and do the same at home. The exception arises to some products though. For example packed fruit juices and pasteurised milk should be refrigerated after opening. Check for such instructions on the package.

Common foods that are refrigerated are vegetables, some fruits, milk, yoghurt, meat and meat products and fresh fruit juices.

Can bacteria grow in a refrigerator?

Yes. This occurs if food is stored for longer than recommended time or if the refrigerator is dirty and contaminated with bacteria.

Both spoilage and pathogenic bacteria can grow. If spoilage bacteria grow, they cause food to have objectionable flavour and smell. However, pathogenic bacteria will not cause such unpleasant odour, flavour or texture to the food. Therefore it is not possible tell if these bacteria are present or not. But once that food is consumed it causes illness.

To avoid such instances, observe strict hygiene of the food and the fridge and store food only for the recommended periods. It is also a good practice to clean the fridge at least once a month.

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