Body Fat Explained

What Is The Purpose Of Storing Body Fat?
Storage of fat on the body is a critical defence mechanism. Remember, the human body has not changed essentially since the Stone Age. At that time starvation and famine were ever-present dangers to survival, while over-consumption and obesity were unheard of. To enable Stone Age humans to survive periods of food scarcity, the human body was designed to store energy which could then be drawn upon in times of famine. Thus for example, people could overeat during the hunting season, or when food was plentiful, and the surplus would be stored as fat tissue (adipose tissue). And when food was short, the body would burn the deposite fat as energy. Of course Stone Age life and body chemistry was/is much more complicated than this simple explanation suggests, but it suffices to explain why we have a built-in fat storage facility.

How Are Carbs, Protein And Fat Absorbed And Stored?
The human body needs energy to power muscles and to fuel the millions of chemical and biological reactions which take place throughout our system every day. This energy comes from the food we consume in our diet. Food consists mainly of water and three types of nutrient - protein, dietary fats and carbohydrate - which are found in varying proportions in most foods. These nutrients are broken down, digested and absorbed by the body in the gastrointestinal tract, running from the mouth to the anus. Each of these macronutrients is processed and absorbed by the digestive system in different ways.

How Are Surplus Carbs Used And Stored?
Carbohydrate is the major source of energy for the body. This is because, of all nutrients, it converts most readily to glucose which is the body's preferred fuel. When we eat carbohydrate, it is converted to glucose in the digestive tract and distributed via the liver to cells throughout the body for use as energy. Once our immediate energy needs are satisfied, the remaining carb glucose is handled in one of two ways. Either it is converted to liquid glycogen (a temporary source of readily available energy) and stored in the liver or muscles. Or, it is converted into fatty acids by the liver and stored in adipose cells (fat-cells) around the body.

How Is Surplus Protein Used And Stored?
Protein is broken down into amino acids in the stomach and small intestine, then distributed via the liver to cells throughout the body for a variety of uses included cell formation and repair. Some surplus protein amino acids are kept circulating in the bloodstream, the remainder is either converted into a type of simple sugar and used as energy, or (like carbohydrate) is converted to fatty acid and stored in adipose cells.

How Is Surplus Dietary Fat Used And Stored?
Dietary fat is broken down into fatty acids and glycerol by the stomach and small intestine. It is then distributed (in the form of triglycerides) via the lymphatic system and bloodstream to the cells for a variety of specialized uses or, in the absence of sufficient carbs, for energy. However, since dietary fat cannot be converted into protein and only about 5 percent (the glycerol part) is convertible into glucose, and because dietary fat is not the body's preferred choice of fuel, a significant amount ends up being stored as body fat in the adipose tissue.

Conversion Of Body Fat To Energy
If energy is required suddenly, the body first uses up its glycogen reserves. After this, it converts the body fat in the adipose cells into energy by a catabolic process called lipolysis. During lipolysis, triglycerides within the adipose cells are acted upon by a complex enzyme called hormone sensitive lipase (HSL). This converts the triglyceride into fatty acids and glycerol. The fatty acids are then transported via the bloodstream to tissues for use as energy, or (along with the glycerol) taken to the liver for further processing.

Adipose Tissue
Adipose cells which make up adipose tissue are specialized cells which contain and can synthesize globules of fat. This fat either comes from the dietary fat we eat or is made by the body from surplus carbohydrate or protein in our diet. Adipose tissue is mainly located just under the skin, although adipose deposits are also found between the muscles, in the abdomen, and around the heart and other organs. The location of fat deposits is largely determined by genetic inheritance. Thus it is not possible to affect where we store fat. Nor is it possible to influence from which area the body burns fat for energy purposes.

Why Do We Get Fat?
Most of us develop body fat because we eat more calories than we burn in exercise. Given a culture which emphasises "value for money food portions" and "super-sizing", along with an steady increase in serving size, an upsurge of new tasty high-calorie foods and energy drinks, such over-consumption is perhaps only to be expected. Lack of exercise is also a major contributory factor. However, overeating and lack of fitness is not the whole story.