The regular practice of physical activity promotes metabolic adaptations that facilitate the regulation of energy and fat balance. These effects are important for a better control of body weight in the obese individual and should enable him or her to involve adipose tissue to a lesser extent in this regulation. Physical activity favours a negative energy and fat balance, particularly if activities are prolonged and vigorous. The achievement of a negative energy and fat balance with physical activity also strongly depends on the nutritional context in which it is performed. In the long term, an active lifestyle and low-fat food habits are expected to induce a substantial body weight loss in the obese. This weight loss is progressively attenuated over time, presumably because of the decreased impact of a reduced adipose tissue mass on the regulation of energy and fat balance. For the obese individual complying with an activity programme and healthy food habits, a body weight loss of 10% is a realistic goal before the occurrence of resistance to further loss of body fat.