2.1 Activity and appetite
As physical activity and food intake are the two key components in energy balance, exercise may have an influence on food intake. Effects on intake are likely to be influenced by the duration, intensity and frequency of exercise. Appetite is a complex phenomenon and is influenced by several factors. In the brain, within a region called the hypothalamus, is the control centre for food intake, the appestat. Many psychological factors influence the desire to eat. Physiological factors, such as blood sugar levels and hormones, also influence the appestat. It is argued that regular exercise helps the appestat to adjust calorie intake to energy expenditure.
It is likely that the types of nutrients in post-exercise food can influence the effectiveness of weight control. In a study on the effects of exercise on energy balance, Tremblay et al. (1994) provided free access to diets of varying fat content to individuals after a 60-minute running session which induced a 500 calorie energy deficit. They found that when exercise was combined with free access to a high-fat diet, individuals were in positive energy balance (750 calories) whereas when exercise was combined with medium- or low-fat diets, individuals were in negative energy balance (-500 and -1000 calories respectively). This suggests that for the exercise to be of benefit in weight loss then high-fat foods must be avoided. Exercise does not provide us with permission to eat high-fat foods; there is a trade-off between the calorie loss from the physical activity and the calorie intake from the foods consumed.