2 Physical activity and appetite
Food intake and physical activity are the two key components in energy balance (the balance of calories consumed through eating and drinking compared to calories used through physical activity).
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 correspond to energy expenditure. Our food intake may be influenced by the duration, intensity and frequency of exercise.
Exercise before eating may inhibit the appetite and increase fat metabolism, since the metabolic rate remains high immediately after exercise (Sharkey and Gaskill, 2013). We previously mentioned the effect of excess post-exercise oxygen consumption (EPOC) on calorie expenditure. Post-exercise may be the best time to eat a meal if weight loss is the goal. Studies have shown that exercise either just before or after a meal is also effective in reducing lipidaemia or lipaemia (the presence of fat in the blood), which is associated with atherosclerosis (the development of fatty plaques in the arteries). Therefore, a post-meal walk or other physical activity is able to reduce lipidaemia by increasing fat utilisation.
Eating food over several periods in the day (three to six), that is, little and often instead of eating a couple of larger meals, has been suggested to lower blood lipid and cholesterol levels, since the metabolism of the fat eaten will occur over a longer period (Sharkey and Gaskill, 2013). In contrast, avoiding meals will lower the metabolic rate and so blood lipids (i.e. cholesterol levels) will increase.
In the next section, you will explore the link between fitness and fat metabolism.