Energy expenditure, body composition and physical activity in humans

The energy expenditure of man can be subdivided into the basal metabolic ra te, the dietary thermogenesis (or thermic effect of food) and the energy ex panded in physical activity. The latter corresponds to the energy expanded to support muscle contraction. The energetic efficiency of skeletal muscle work is about 25 %. In sedentary individuals, the energy expanded in physic al activity represents a relatively minor portion (20-30 %) of daily energy expenditure. Obesity results from an imbalance between energy intake and e xpenditure, resulting in positive energy balance during the period of weigh t gain. At the phase of obesity maintenance, an even energy balance is rest aured through an increase in body weight ana lean body mass. During overfee ding there is little adaptative changes in energy expenditure. Overfeeding has no marked effect on basal metabolic rates or on dietary thermogenesis. Recent observations however suggest that stimulation of physical activity m ay occur in some individuals during overfeeding, and may contribute to prev ent or limit weight gain.