Hormones

Vegan men have the same free testosterone as meat-eaters

By WhyStopHarmingAnimals.com

Vegan men do not lose testosterone[1][2]. In the larger of two comparisons, 696 men split between meat-eaters, vegetarians and vegans, the 233 vegans had higher total testosterone than either of the other groups[1].

They also had more sex hormone-binding globulin[1], the protein that carries testosterone in the blood and holds it out of action while bound. The extra binding offset the extra testosterone, so free testosterone, the fraction available to act on tissues, came out the same in all three groups[1].

Two measurements, one pattern

The 2000 study, published in the British Journal of Cancer, repeated what an earlier and much smaller study had found[1][2]. In 1990, researchers compared 51 vegan men with 57 omnivores[2]. The vegans had 7% higher total testosterone and 23% higher binding globulin, leaving free testosterone and estradiol effectively unchanged[2]. The sample was small, but the larger study found the same shape a decade later.

The 2000 study turned up one real difference. The vegan men had 9% lower IGF-1[1], a growth factor that promotes cell growth and whose higher levels are linked with higher risk of some cancers. Both studies are observational: they measured men who already ate these ways, rather than switching anyone's diet.

Soy does not feminize men

The worry usually comes down to soy. Soy contains isoflavones, plant compounds with a weak estrogen-like structure, and the claim is that tofu or soy milk will lower a man's testosterone or raise his estrogen.

That has been tested directly and repeatedly[3][4]. A 2021 meta-analysis in Reproductive Toxicology pooled 41 clinical studies in men[3]. Neither soy protein nor isoflavones changed total testosterone, free testosterone, estradiol, estrone or binding globulin, at any dose or duration tested[3].

An earlier meta-analysis, published in Fertility and Sterility in 2010, reached the same answer[4]. It pooled 15 placebo-controlled treatment groups and assessed 36 more in simpler models[4]. Neither soy protein nor isoflavones changed testosterone, free testosterone, binding globulin or the free androgen index in men[4].

Unlike the diet comparisons, these are clinical studies, where men were given soy or isoflavones and their hormones were measured[3][4]. Across both analyses and dozens of trials, the feminization claim has no data behind it[3][4]. Vegan men, soy included, have the same free testosterone as men who eat meat[1][2][3][4].