|Obesity is a term applied to people who are overweight and have excess body fat. It is one of the most common problems in the developed world. However, it is normal and desirable to have some reserves of fat in the body. In lean men about 16 per cent of body weight is fat at age 25, increasing to 24 per cent by age 65. In lean women, about 30 per cent of body weight is fat at age 25, increasing to about 36 per cent by age 651. This article investigates the health implications of exceeding these guidelines.