Question
Does eating soy reduce testosterone levels in men?
Answer
No.
Explanation
In a 2010 meta-analysis of research into whether soy protein or isoflavone intake has estrogen-like effects in men, 32 studies were analysed (of which 15 were placebo controlled and included baseline and ending measurements).
No statistically significant effect was found on the levels of testosterone (T), free testosterone (free T), sex hormone binding globulin (SHBG), or the free androgen index (FAI).
Sources
Hamilton-Reeves, J.M., G. Vazquez, et. al., Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis (Fertility and Sterility journal, Vol. 94, No. 3, August 2010)