Weight management and exercise

I am often shocked when I meet former champions and realise that they have put on dozens of excess kilos. Admittedly this is not the rule: most ex-athletes manage to keep their weight under control but I have met too many overweight ex-champions to ignore a definite tendency to gain weight once one stops heavy training. This got me thinking on the relation of exercise to weight control and I decided to dig deeper.

The widespread belief is that exercise plays an important role in weight management. Just pick up jogging (or any similar moderately strenuous exercise) and you are going to shed your extra kilos. Alas, the situation is not that simple. When you count the extra calories burnt during the exercise, you realise that they do not amount to much. And thus the mantra of nutritionists became "if you wish to lose weight go on a diet". And they are essentially correct. But does that mean that exercise is useless when it come to controlling ones weight? Far from it!

To put it in a nutshell, the best way to prevent weight gain is a combination of diet with exercise. Exercise alone will not suffice for diminishing ones weight (but it becomes more and more effective when its intensity increases). However it does prevent a weight gain and, what is perhaps even more important, it prevents regaining the weight that has been previously lost (perhaps by a combination of diet with exercise).

But how does exercise manage to help in weight control? Most people believe that exercise increases one's appetite and as a result one eats more and gains weight. It turns out that this belief is plainly wrong. Already in the 50s a study on Bengal workers obtained some very interesting results. Active people ate more, in proportion to the intensity of their work, but remained in a calorie balance, with no excess body weight. Sedentary people on the other hand ate more and were overweight.

As one can imagine similar studies have been performed many times since and the initial results were fully confirmed. The relation between physical activity and appetite follows the curve shown in the diagram below. Sedentary people eat more than they should while active people adapt their intake to their levels of activity.

So the question is, what does cause this difference? A recent study has addressed this question and the conclusion is that exercise facilitates weight control, partly through its effect on appetite regulation. The belief that exercise does increase the appetite is well-founded. However this effect is counterbalanced by an improvement of the sensitivity to signals of satiety. One may feel hungrier after exercise but thanks to the latter one is less prone to overeat. Exercise enhanced appetite control is most beneficial to losing weight, or maintaining lost weight, since one is more sensitive to feelings of hunger and satiety.

These are solid conclusions based on observations but what is lacking is a deep explanation of how exercise regulates appetite. Physiological factors, like levels of insulin, have been proposed as a possible explanation. A theory that I ran across in an article that largely inspired mine is that of the "hungry ape". Humans evolved in a food-poor environment and had thus the tendency to gorge themselves when they encounter abundant food. On the other hand the body resists gaining weight, since becoming fat and slow diminishes the chances of survival. Physical exercise maintains the mind-body link while a sedentary life leads to a dissociation of the two and thus an unnatural increase of body weight. 

Another theory which I find appealing is one based on the relation of exercise to anxiety and depression. It has been known for years that exercise is just as effective as antidepressants. And the same is true as far as anxiety is concerned. Sedentary people often use food as a source of comfort, while active people turn to exercise as a source of feel-good sensations.

So while diet is incontrovertible if one wishes to lose weight, an exercise regime does help to the point where dieting becomes almost a reflex. Faced with the cornucopia of food (I am referring here to our western societies, where food abundance is the rule) a physically active person is more prone to ask himself whether he is really hungry or whether it's the food that is overly tempting instead of blindly succumbing to the temptation. Thus, thanks to exercise, maintaining a calorie balance becomes a way of life and weight control is automatically taken care of.