American Fitness Professionals & Associates

For women, the rules may be different. Exercise uses energy. Energy, the first law of thermodymnamics tells us, can’t be created or lost. It merely changes form. So if a human being carries out exercise, the energy to do so must come from somewhere.
This is either from food sources in the diet, or from body fat stores on the body - from the extra fat stores around the middle of men, or the hips and buttocks of (premenopausal) women.  

That’s the theory. But the practice seems a little different when it comes to the sexes. If you hadn’t noticed, women seem to have a little more trouble than men losing those extra pounds - even with the extra pounding of the pavement.

In fact, this has even been noticed by scientists working in the field. So much so, that one group, from the University of Maastricht in the Netherlands, has set out to show the differences in body fat content between men and women associated with the amount of exercise they carry out.

Professor Klaas Westerterp is a highly well respected researcher in the field. Unlike previous researchers who have estimated exercise expenditure through questionnaires and other less reliable means, Westerterp and his colleagues have pulled together all the available research using the ‘gold standard’ measure of energy expenditure - doubly labelled, or radioactive water.

This simple technique enables exact energy measurements by calculating the differences in radioactive water consumed and passed through the system in urine.With some untypically large numbers from his research, Westerterp has shown, quite convincingly, for the first time, that exercise levels and body fat are totally unrelated in women, whereas in men, there is a clear inverse correlation. In other words, exercise seems to decrease fat in men, but not in women. Why?

Going back to the first law of thermodynamics, it must come back to the amount of food eaten. From other research, it’s now clear that women who exercise overcompensate by eating more - without necessarily being aware of this. They do so for obvious evolutionary reasons. The female body needs extra fat stores (about 10% more than men) to make sure they get through the 9 months of pregnancy. Males have no such need to survive after conception.

What does all this mean? Firstly, that women are less likely to respond to exercise with decreases in body fat. The idea of exercise for weight control for women just doesn’t have the same value. Secondly, if exercise is to have a role in body fat maintenance, it has to be strictly combined with a controlled food input program with women. With men on the other hand this seems to happen as a matter of course.