How and where we store fat in our bodies is decided, before we are born, by the formation of layers of tissue (called adipose tissue). This tissue consists of a fibrous framework containing fat cells that store fat: this is their special purpose.
When we take in more kilojoules than are needed to supply energy, the excess is stored as fat in the special cells of adipose tissue, which expand by accumulating fat droplets inside their cell membranes. The layers of adipose tissue become thicker as more fat is stored in its cells. When our food intake supplies less energy than we need, stored fat is released from fat cells to be converted to energy, and adipose tissue layers become thinner.
Fat can be stored only in adipose tissue, which is present under the skin, beneath and between the layers of the membrane that line the abdominal cavity, and around some of the internal organs, including the kidneys and heart. There are two types of adipose tissue. In one (let’s call it type I) the fat cells are distributed evenly throughout the tissue framework and as the cells are expanded by fat storage, the tissue enlarges evenly. When fat stores are used up, fat tends to be lost early from this tissue. Type I fat storage is predominant beneath the skin of the abdomen, upper trunk and neck.
In the other type (we’ll call it type II) fibrous strands in the framework divide the tissue into compartments that tend to bulge as more fat is stored, giving a dimpled appearance to the overylying skin. This type of adipose tissue is sometimes called ‘cellulite’, and it is most likely to be found in localised pads on the buttocks, hips and thighs, especially in women. Type II fat is the last to go when weight is lost. In general, it tends to be independent of overall body weight: many women retain their ‘jodhpur hips’ when they are quite slender elsewhere. It would probably take an unhealthy weight loss to shift all this fat.
Each of us has an inherited capacity for fat storage and a unique shape that depends on how much of each type of adipose tissue we have and where it is. The majority of women have fat storage tissue mainly on their thighs, buttocks and abdomen, but there are also those with skinny thighs and bottoms who store fat in their breasts and upper arms. We also vary as to how tough are the strands that divide up type II fat and how far apart these strands are: bigger compartments make more obvious dimples. This is why dimpled fat shows up more in some women than in others.
These inherited characteristics of fat storage and body shape can’t be changed, just as we can’t change the colour of our eyes. Inheritance is also one reason why body shape and leanness or fatness tend to run in families: another reason is that eating habits also run in families. Also, the rate at which we burn up energy, and thus how much is left over for storage, seems to be at least partly inherited. We all know people who regularly consume huge meals and remain lean, and others who seem to eat very lightly and still put on weight.
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