In the 70s, more than 12,000 Adventist men were asked about their use of soy milk, and then, they were followed for up to 16 years to see who got cancer, and who did not. So: “Does high soy milk intake reduce prostate cancer incidence?” “Frequent consumption…of soy milk was associated with a whopping 70 per cent reduction of the risk of prostate cancer.” Similarly, in a “Multiethnic…Study” that involved a number of groups, soy intake appeared protective in Latinos, too.

A systematic review of all soy and prostate cancer population studies to date confirmed soy foods "could lower the risk." But that's kind of a broad category. There's all sorts of soy foods. There's fermented soy foods, like miso and tempeh, and unfermented foods, like tofu and soy milk. Which is more protective? Researchers sifted through the studies. And, it turns out that only the unfermented soy seemed to help. Tofu and soy milk consumption were associated with about a '30% reduction in risk, whereas there didn't appear to be any protection linked to fermented soy foods.