Examine has a good writeup, jump to "Men’s health and testosterone" tl;dr: "Reasonable intakes of soy foods and soy isoflavones do not affect men’s testosteron

Examine has a good writeup, jump to "Men’s health and testosterone" tl;dr: "Reasonable intakes of soy foods and soy isoflavones do not affect men’s testosterone levels, estrogen levels, or fertility, although case reports have documented adverse effects from incredibly high daily intakes of soy for 6–12 months. Men who are at risk of developing prostate cancer might reduce their risk by eating soy foods, but soy foods do not appear to benefit men who already have prostate cancer." The case studies regarding feminization seem to have been cases of people ingesting 300+g of soy protein a day for 6+ months. That amount of protein would require nearly 100% of your calorie RDA if eaten in soybeans, so it seems likely these two people had quite odd diets that could confound drawing conclusions these cases. If they were taking a soy protein extract, I would want to study if questionable supplement purity/contamination issues had any effect - solvents and heat could transform some of the isoflavones or solvents could remain in final product. https://examine.com/nutrition/is-soy-good-or-bad/ https://examine.com/nutrition/is-soy-good-or-bad/