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Does soy protein have any place in bodybuilding?

This is an age-old question in bodybuilding and other sports circles, and that’s because there’s a lot of research to wade through on either side of this debate. On the one hand, it’s a simple fact that soy proteins do contain phytoestrogens. These are plant compounds that have estrogenic effects on the cell. On the other hand, some people argue that when the weak soy phytoestrogens bind to the cell’s receptor, it may actually block the effects of the stronger estrogen hormones produced by the body. One study showed decreased testosterone levels and increased estrogen-receptor activity in men using almost 60 grams of soy protein daily for a month, and when they stopped taking it, their test levels shot back up. (The researchers didn't mention whether the men had a sudden urge to shop for shoes and purses.)

Studies in animals raise concern about soy protein’s effects on hormone and reproductive function, but humans metabolize phytoestrogens differently than animals. Also, the biggest review to date concluded that there’s not enough evidence to show that soy decreases testosterone or free testosterone levels in humans. But on the other hand, that doesn't rule out estrogen-like effects.

Pediatric doctors who treat babies certainly have their concerns about soy. The advice for infants is that soy-based formula should only be used as a last resort for male babies because of case reports of estrogenic effects (such as breast development in boys). So there’s something going on here hormonally!

Sorry, I can’t just give you a straight answer on this one, but the bottom line regarding whether bodybuilders should use soy protein is that no one knows if it will have negative effects or not.