FAT GAINS AND LOSSES
Fat is either gained or lost by increases or decreases in the size of the lipid pool in large numbers of fat cells. These ‘fill up’ in good times, like a water tank after heavy rain, and ‘empty out’ in bad times, like in a drought.
Which cells fill up or empty out most, and in what order, is a function of a range of factors including genetics, gender, age, race and the number of existing fat cells. One thing is clear though: the last cells to fill up are likely to be the first to empty out. If someone gains extra fat around the waist for example, this will usually be the first place it goes from when the energy balance becomes negative.
Fat cell enlargement through expansion of existing cells is called hypertrophy. A less common way of increasing fat is through an expansion of fat cell numbers or hyperplasia. Hyperplasia is
thought to occur only at certain periods in life, in particular during growth spurts when all body cells are rapidly increasing in number, such as early infancy (1-2 years) and early adolescence (12-14 years). Inappropriate lifestyles at these times may lead to a greater increase in fat cell numbers than might otherwise occur. A third stimulus to hyperplasia which is now well recognised is a large increase in body fat. As existing fat cells ‘fill up’, new cells come into existence and form a bigger ‘maximum capacity’ which is then capable of storing a total greater volume of fat. In contrast to the 30-50 billion fat cells of the average person, an obese person may have 70-80 or even up to 100 billion adipocytes.
Not a lot is known about these precursors; whether they are actually small fat cells in waiting, or whether they are just other (’stem’) cells that can be called on to make any other form of cell if needed. Some research suggests that they spring into action during the growth spurts mentioned above if conditions are right, or when increases in body weight exceed around 170 per cent of ideal or average weight. Once they mature however, they are there for life. Animal research has shown that with severe dietary restriction, fat cells can shrink to the point where they are virtually unrecognisable as adipocytes, but when overfeeding begins again, the shrunken cells rapidly fill up with fat.
With the expansion of fat cells in the waist region, some men, in particular, develop a ‘hard’ fat belly and some a ’soft’ or ‘wobbly fat one. The reasons for this are not quite clear but it’s possible that the big, hard abdomen represents a larger degree of visceral fat within the abdomen, which then pushes out more on the inner surface of the abdomen. Fat which is more ‘wobbly’ may represent more subcutaneous fat, although the evidence for this is not currently clear.
Irrespective of the type of fat stored, it’s clear that it is easier to prevent obesity and overfatness beyond a certain level than to cure it. Obviously, the function of fat as an energy store means that the human body has a certain capacity for increases and decreases in fat stores without permanent change. In the long term and for the very obese, however, there may be more permanent changes in fat cell numbers, metabolism and other fat maintaining factors, which make it more difficult to reduce body fat levels. People in this situation and those with a strong genetic component may be structurally and functionally different to the mildly overfat and in fat loss programs their outcomes may not be as favourable. They might need different programs to achieve similar levels of success as programs aimed at mildly fat people.
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