Regular physical activity has profound effects on body composition and the utilisation of nutrients and help to maintain and increase skeletal muscle mass, with increased resting metabolic rate and enhanced capacity for lipid oxidation during rest and exercise. Regular exercise may also prevent or limit the loss of lean tissue (fat-free mass, FFM) during slimming regimens. Increased physical activity induces a number of favourable changes in the metabolism of lipoproteins: serum triglycerides are lowered by the increased lipolytic activity, the HDL concentration increases and the concentration of small dense LDL decreases. In addition, the enhanced metabolic capacity of skeletal muscle (metabolic fitness) will favorably influence risk factors such as insulin resistance and hypertension. Because regular physical activity has favorable effects on several of the comorbid conditions of obesity, particularly cardiovascular disease and type 2 diabetes, it is not surprising that the mortality rates seem to be lower in the overweight and moderately obese individuals who are physically fit compared with the unfit. The treatment of overweight and obese persons should perhaps be more focused on the level of regular physical activity than on body weight per se. For most of those who wish to reduce their body weight, it is recommended that they combine regular physical activity with a somewhat reduced energy intake, in particular of food rich in fat. Emphasis should be on promoting relatively low-intensity, long-duration physical activity which can be conveniently incorporated into daily life.