Obesity and physical activity.

OBJECTIVES: Three aspects of obesity and physical activity are reviewed: whether the obese are inactive; how the activity level can be increased; and which are the effects of an increase in physical activity in combination with a reduction of energy intake.
METHOD: The focus is on an objective approach that is, activity associated energy expenditure as measured with doubly labelled water.
RESULTS: Activity associated energy expenditure increases with body mass index while the average physical activity level does not change. The majority of obese subjects is moderately active. An increase in the activity level of obese subjects is limited by the ability to perform exercise of higher intensity. Training programs obese subjects can cope with are until now not rewarded by weight loss. A possible loss in fat mass is compensated by a gain in fat-free mass.
CONCLUSIONS: Obese subjects can only reach a significant weight loss with an energy restricted diet. Mild energy restriction will already result in very significant weight loss when one complies with the diet. An increase in physical activity is necessary to compensate for the reduction in activity induced energy expenditure and should be facilitated by the lower body mass.