Narrator: This is Science Today. The so-called spare tire many men acquire as they hit middle-age is not just for couch potatoes. Scientist Paul Williams of the Lawrence Berkeley Laboratory says waistline expansion may be unavoidable, even amongst serious athletes.
Williams: We've known from other studies that as men get older and they reach middle-age, they start to gain a few inches around their waistline. We wanted to find out if men who are very active could avoid this and in fact, the bad news was: no, this doesn't seem to be the case.
Narrator: Williams studied seven thousand runners and found that up to the age of 49, increases in weight seemed to be the same in men who were not as physically active. The reason is not very clear.
Williams: There have been some studies that have looked at changing testosterone levels in men. We know that these levels go down, that this may correspond to the weight gain and in fact some studies show that when you give men testosterone there is a weight loss and indeed and improvement in cholesterol levels.
Narrator: While more research on testosterone is conducted, Williams says to compensate for this middle-age spread, men should add miles to their running routine, not cut back. For Science Today I'm Larissa Branin.