You know, I have a friend who's a physician, and she says that body fat secretes testosterone.

Yeah, weird, I know.

Anyway, she says that excess fat can alter your hormonal makeup so much that you become infertile.

Anyway, if that's true (and she would know), then it would follow that as you lose body fat, your hormonal makeup would change. Your body's production of etrogen and progersterone would likely be affected by the drop in testosterone levels -- though I don't know exactly what would happen. (But I know, for example, that men who use steroids -- which are very similar to testosterone -- to build muscle also have wind up having increased levels of estrogen such that they sometimes grow breasts. If one hormone is out of whack, the others will be too.)

But then, I think the effect of fat on hormones typicaly occurs only in people who are quite obese. If you're only moderately overweight, you probably can't blame altered hormones on fat loss (or gain).