Effect of exercise on food intake in human subjects

We review human studies of the effect of physical activity on food intake. Most are flawed by inaccurate measurement of energy expenditure and/or energy intake, by lack of controls, or by short study periods. While lean persons seem to regulate and maintain weight well, studies in obese subjects are inconclusive. At realistic exercise intensities, the effect on weight is generally small. There is little evidence of inhibition of food intake. In our metabolic ward studies, treadmill exercise neither enhanced nor inhibited food intake in obese individuals. Since intake remained fixed, a negative energy balance was observed with exercise. When more savory food was provided, intake again remained fixed as exercise was increased, but subjects ate more throughout and maintained positive energy balance. Thus, energy output does not regulate energy intake closely in the obese. Food-related cues seem more important than exercise-generated signals. The beneficial effect of exercise on body weight is limited to the extra calories expended. Further careful studies are essential to differentiate effects of kinds and intensities of exercise.