Exercise, Appetite, and Energy Balance: The Interactions Between Energy Expenditure and Intake, and the Implications for Weight Management

Abstract

A low level of physical activity, typical of Western society, is deemed conducive to weight gain, while an increase in physical activity tends to promote weight loss, suggesting an imperfect coupling between energy expenditure and intake. Conversely, individuals with high levels of habitual activity tend to be in energy balance over the long-term suggesting that intake is adjusted to match expenditure. There are four interactions to consider between energy intake and expenditure in the development and treatment of obesity. Does exercise drive energy intake upwards and undermine its contribution to weight management? Does sedentariness alter levels of energy intake or subsequent energy expenditure? Do high levels of energy intake alter physical activity or exercise? And does dieting elevate or decrease energy expenditure? Cross talk between elevated energy expenditure and intake is initially too weak and takes too long to activate, to seriously threaten dietary approaches to weight management. It appears that substantial fat loss is possible before intake begins to track a sustained elevation in expenditure. There is little evidence that sedentariness produces compensatory reductions in energy intake. This lack of cross talk between altered expenditure and intake tends to promote a positive energy balance. Sizeable, compensatory changes in nonexercise activity in response to overfeeding are feasible, but have yet to be clearly demonstrated. There is more evidence that energy intake restriction does lower physical activity levels (PALs) – at least when it is more severe and for longer than is recommended for normal dieting and weight loss. A higher level or duration of physical activity is needed to prevent weight regain after dieting than is needed to prevent weight gain in the first place. Even more is needed to achieve weight loss through exercise alone. Individuals who are regularly physically active tend to be leaner and have a lower body weight than those who are sedentary. Taking up regular exercise results in weight loss or maintenance, while stopping results in weight gain. However, individuals vary in their ability to adjust or regulate the various components of energy balance, and therefore in their resistance to lose or gain weight in response to increases or decreases in energy expenditure respectively.