A person is usually considered obese if they weigh 100 lbs more than the desirable weight or twice the desirable body weight.

Fat deposits are one way for your body to store energy. Hormones, such as insulin and steroids, control the metabolism of fat.

In the legs and trunk, the fat beneath the skin has two layers, deep and superficial.

The deep layer is loosely organized. Each person has a pattern of fat deposition that is quite individual and determined by the amount of fat in this deep layer. This is the layer which is removed during traditional liposuction. The superficial layer is more dense and the fat is contained within pockets by fibrous bands. This is a cause of cellulite. This layer is difficult to change with traditional liposuction but may be helped with ultrasonic liposuction .

The distribution of fat depends on a person's age, sex and race. Obesity can be a predisposing factor to eating disorders, especially in men.

Women tend to have more fat than men and it is found mainly in the hips, buttocks and upper thighs. Men tend to have more fat in the abdomen and the back of the neck.

The size and number of fat cells increase during the first five or six years of life. Although there may be an increase in the amount of fat during our teenage years, the number of cells usually remains constant. As we grow older the fat tends to leave the legs and relocate more centrally. This causes the well known "spare tire". The fat also goes internally, to lie inside the abdomen. The fat in the legs disappears from beneath the skin and is deposited within the muscle.

In severe obesity, the number of fat cells or adipocytes, may increase even in adults. This is why it is more difficult for very obese people to lose weight. The type of obesity associated with an increase in the number of cells, is called hyperplastic obesity. Dieting and exercise are less effective in this situation. Abdominoplasty may be the only answer for these people. Traditional liposuction is not appropriate for obesity but ultrasonic liposuction may help.

In a more modest increase in weight, the amount of fat within the cells increases, but the number of cells does not change. This is called hypertrophic obesity and will usually respond to changes in life style. If it is localized liposuction may help.