Hormones
Vegan men measured higher total testosterone and lower IGF-1
SameFree testosterone in vegan, vegetarian, and meat-eating men
Among 696 men, vegans had 9% lower IGF-1 and higher total testosterone than meat-eaters and vegetarians[1]. Higher binding globulin offset the testosterone[1], so free testosterone was the same[1]. An earlier measurement found the same pattern[2]. Across 41 clinical studies, soy protein and isoflavones did not change male hormones at any dose tested[3], and an earlier 15-group meta-analysis agreed[4]. Soy does not feminize men[3][4].
What the evidence says
The main points first. Every claim is tied to a source below.
Vegan men had higher total testosterone, lower IGF-1, and the same free testosterone
Among 696 men, the 233 vegans had 9% lower IGF-1 and higher total testosterone than meat-eaters and vegetarians[1]. Higher binding globulin offset the testosterone, so free testosterone was the same in all three groups[1]. An earlier sample of 51 vegan and 57 omnivore men found 7% higher total testosterone and 23% higher binding globulin[2], leaving free testosterone and estradiol effectively unchanged[2].
Read full article →Soy does not feminize men
Across 41 clinical studies, neither soy protein nor isoflavones changed total or free testosterone, estradiol, estrone, or binding globulin, at any dose or duration tested[1]. An earlier meta-analysis of 15 placebo-controlled treatment groups found the same in men for testosterone, free testosterone, binding globulin, and the free androgen index[2]. The trials give the feminization claim nothing to stand on.
Read full article →Articles
Vegan men have the same free testosterone as meat-eaters
Vegan men measured higher total testosterone and the same free testosterone as meat-eaters, and 41 clinical studies found soy does not change male hormones.
Read full article →
Sources
Papers and datasets. Each card keeps its caveats, including small samples and single-animal cases.
[1]British Journal of Cancer, 2000 · Observational
Vegan men — testosterone and IGF-1
Among 696 men, the 233 vegans had 9% lower IGF-1 and higher total testosterone than meat-eaters and vegetarians. Higher binding globulin offset the testosterone, so free testosterone was the same in all three groups.
[2]British Journal of Nutrition, 1990 · Small sample
Vegan men — the earlier hormone measurements
In 51 vegan and 57 omnivore men, the vegans had 7% higher total testosterone and 23% higher binding globulin, leaving free testosterone and estradiol effectively unchanged.
[3]Reproductive Toxicology, 2021 · Meta-analysis
Soy does not feminize men
Across 41 clinical studies, neither soy protein nor isoflavones changed total or free testosterone, estradiol, estrone, or binding globulin, at any dose or duration tested.
[4]Fertility and Sterility, 2010 · Meta-analysis
Soy and male hormones — the earlier meta-analysis
Fifteen placebo-controlled treatment groups, with 36 more assessed in simpler models: neither soy protein nor isoflavones changed testosterone, free testosterone, binding globulin, or the free androgen index in men.