The relationship between physical activity and food intake.

It is a commonly held belief that exercise (one method of inducing an energy deficit) causes a compensation in energy intake to match the exercise-induced energy expenditure. This could possibly lead to the belief that exercise is not a useful method of weight loss which could then be used as an excuse not to exercise. However, there is no compelling evidence to suggest that exercise drives hunger and energy intake to cause a compensation in food intake. Indeed, the evidence suggests interventions in energy expenditure are not compensated for by changes in energy intake at least in the short-term (see King et al. 19976 for a review). This suggests only weak short-term coupling between energy expenditure and energy intake. However, since the negative energy balance could not continue indefinitely an equilibrium of energy intake and energy expenditure must occur at some stage. The exact time course (and mechanism) of such a compensatory change in energy intake is not yet known. A ‘delayed’ compensatory response to physical activity has been suggested (Edholm et al. 1955; Edholm, 1977), but this phenomenon has never been replicated. One other issue concerns the effects of exercise on changes in food selection or food preferences. Another widely held belief is that exercise induces an increase in the selection of carbohydrates. The evidence for a short-term effect is not convincing, but in the long-term carbohydrate intake does increase with prolonged exercise (Wood et al. 1982). This effect could be biologically driven or occur as a result of changes of a psychological nature. At the present time some effects of exercise on appetite are clear whereas other aspects require more research. The interactions are likely to involve both physiological and psychological processes. With the renewed interest in physical activity for body weight control, it becomes increasingly important to understand more fully the effects of exercise on the control of appetite .