ABSTRACT
The volume of physical activity needed to prevent obesity is greater than general public health recommendations, probably 150 to 250 minutes of moderate to vigorous aerobic activity per week. There is no strong evidence to suggest that physical activity stimulates appetite, but nevertheless the choice to eat more can lead to failure of exercise-based weight-loss programmes. A negative energy balance also decreases resting metabolic rate, in part because tissue mass is decreased. However, resistance exercise counters this by conserving lean tissue. There is little evidence that a moderate exercise programme induces a compensatory reduction of leisure activity. Cross-sectional studies show a low body fat content in physically active groups such as physical education students and traditional Amish communities. Body fat levels are also inversely correlated with self-reported and objectively measured habitual physical activity. Further, increases of body fat are seen with the adoption of a sedentary lifestyle. In prospective studies a spontaneous increase of habitual physical activity limits fat accumulation, and in randomized trials an increase of physical activity reduces body fat content in the intervention group.
