Q&A: Will a high-soy diet affect fertility?

Soy is a source of isoflavones, which supply natural estrogen. If you consume enough, it is theoretically possible to overlay your normal cyclic hormonal fluctuations with a steady stream of dietary hormones. If your cycling nature is overcome, this could disrupt ovulation and hinder fertility.

For all of the things a period may be to someone, it's also a signal that everything's usually working right. If you've affected the cycle enough (with natural estrogens or medications) such that ovulation is interrupted, then your periods are going to get screwed up as well. So my answer is that if you're cycling normally with your periods, you're probably ovulating normally, too. If you're on birth control pills, the point is moot, since the birth control pills are a steady stream of hormones, suppressing your normal cycle anyway. And even if you've messed up your cycles with dietary estrogens, simply removing the source of the interference should bring about a complete return to normal, just as getting off birth control pills should bring about a return of natural cycling.

Interestingly, dietary supplements and choices aren't the only things that can pollute the cycle. Fat cells have a metabolism besides just lying there adding bulk. They convert an adrenal hormone, androstenedione, into estrone, an estrogen. So overweight women may have a steady flow of estrogen mucking up the works, resulting in abnormal and persistent vaginal bleeding, called dysfunctional uterine bleeding. These women have trouble ovulating and therefore don't routinely enter the second half of their cycles. The period that follows a second half doesn't occur, until the lining of the womb gives up and sheds irregularly.

Your regular monthly period can usually be the "all clear" that you're not affecting anything. If your periods are irregular, your healthcare provider can help get you straight again.