Isn't soy bad for you (hormones, men's health)?

The objection

“Soy is full of phytoestrogens. Eating a lot of it will mess with a man’s hormones.”

The answer

The word “phytoestrogen” contains “oestrogen,” and that’s where the fear lives. But phytoestrogens are not human oestrogen. They are plant compounds that bind weakly and selectively to oestrogen receptors, preferentially the beta receptor, which often produces effects different from, or opposing, the body’s own oestrogen. Calling them “oestrogen” because they share a receptor is like calling a key a lock because it fits the keyhole.

So what happens in actual men eating actual soy? We don’t have to guess. Reed and colleagues (2021) pooled 38 clinical studies, the largest meta-analysis to date, and found neither soy foods nor isoflavone supplements significantly affected total testosterone, free testosterone, oestradiol, oestrone or SHBG in men. No measurable feminisation. The viral “man grows breasts from soy” case involved roughly three litres of soy milk a day, far beyond any normal diet.

There’s a twist the objection never anticipates. For breast cancer, the disease soy fear most attaches to, the evidence points the other way. A pooled analysis of US and Chinese cohorts found soy intake after diagnosis was linked to lower recurrence and lower mortality, with intakes around 10 mg of isoflavones or more per day associated with roughly a 25% reduction in recurrence. The American Cancer Society now considers moderate soy safe for survivors.

One caveat for honesty’s sake: most of the protective data is observational, and more isn’t better, since benefits plateau at food-level intakes rather than megadoses of isolated supplements. Nobody is claiming soy cures cancer. The point is that soy, eaten as food, is safe for men and probably protective against the very cancer it was accused of causing.