Soy did not move testosterone in 1,753 men
Across 41 clinical studies of soy foods, soy protein and isoflavone extracts, neither testosterone nor free testosterone, oestradiol, oestrone or sex hormone binding globulin shifted.
What the study found
Testosterone was measured in 1,753 men and did not move
Across 41 clinical studies of men eating soy foods, soy protein or isoflavone extracts, neither testosterone nor free testosterone, oestradiol, oestrone or sex hormone binding globulin shifted. Splitting the studies by isoflavone dose and by trial length uncovered no effect either.
The caveat · Dihydrotestosterone was never pooled
Two of the five authors have soy-industry ties, one directing an institute funded by the United Soybean Board, and the same group produced the earlier analysis this one updates. Dihydrotestosterone was left out of the pooled outcomes, and it is the one androgen a soy effect has been reported for.
What we don't know
Soy's clean record on male hormones leaves out dihydrotestosterone, the one androgen a crossover trial saw fall by 9 to 15 percent. Both can be true because they measured different things; nobody has pooled the hormone that moved.