Exceeding the normal weight by more than 20 per cent. The normal weight is calculated on a basis of height, age and sex. The Quetelet index is also often used as a measure of overweight. For this purpose the weight in kilograms is divided by the square of the height in metres. If this calculation results in a figure between 20 and 24, the weight is within the norm, whereas if the figure is higher than 27 it is possible to speak of obesity. Obesity is always the result of food intake larger than the body requires. The excessive amount of energy which has been absorbed is stored by the body in the form of fat. Food which is rich in calories (with much fat and many carbohydrates or sugars) assists the production of body fat. The same applies to alcohol, which also contains a large number of calories. The excessive storage of body fat is hardly ever caused by disease, and it is therefore not generally useful to carry out an extensive examination in order to detect particular metabolic disturbances such as a thyroid gland which is underfunc-tioning. Obesity should be distinguished from conditions in which the amount of liquid in the body is increased (oedema). Body weight also increases in oedema, but this is usually only temporary. When the cause is treated (it may be cardiac weakness or nephritis), surplus body fluid is lost by urination and the weight can decrease by several kilograms in a few days. Obesity can have a number of harmful consequences. Firstly, the percentage of fat in the blood practically always increases, and this furthers fatty degeneration of the arteries (atherosclerosis). Secondly, obesity increases the possibility of high blood pressure and diabetes. Support joints (ankles, knees and hips) are overloaded, and wear and tear (arthrosis) can occur as a result. Other possible consequences of obesity are hiatus hernia, gallstones and varicose veins. Treatment of obesity is directed towards its cause, and therefore consists in limiting calory intake and increasing the rate at which the body burns them up. The intake can be reduced by altering eating habits. A fundamental change in eating patterns, which is adhered to, gives a much better chance of lasting results than a short period of strict dieting. In addition, physical exercise is also useful in order to speed up the burning of calories. Medication is not recommended for obesity. Drugs which inhibit the desire to eat should not be taken over a long period because they may have side-effects. This applies particularly to hormone preparations such as thyroid gland hormones. It is also not suitable to use diuretics in order to combat overweight. As the name indicates, they lead to the elimination of liquid, and not of fat, so weight loss achieved by this means is not permanent, and there is a danger of dehydration.