The claim
“Eating soy lowers testosterone in men.”
False
Evidence confidence
Strong
Strong confidence because an updated meta-analysis of controlled clinical studies found no effect of soy protein or isoflavones on total or free testosterone in men across study doses and durations. The earlier meta-analysis reached the same conclusion but is superseded by the update.
The facts
Controlled human studies do not show that soy foods or isoflavone supplements lower total or free testosterone in men. They also do not show a consistent rise in estradiol or estrone.
What this means for you
There is no evidence-based reason for most men to avoid tofu, tempeh, edamame or soy milk because of testosterone concerns.
Your next step
Choose soy foods based on nutrition, taste and tolerance rather than fear that they will lower testosterone.
Sources