Does a Plant-Based Diet Lower Testosterone? What the Studies Actually Show

If you type “vegan testosterone” into a search bar you will find two camps shouting at each other. One says plants will soften you. The other says plants will supercharge you. Neither is reading the studies.

I eat plant-based and I wrote a book about male vitality, so I had every incentive to find the flattering answer. What I found instead was a fairly boring one, and boring is good news here.

The direct evidence: no association

The cleanest study on this exact question was published by urologists at the University of Miami in the World Journal of Urology (Kuchakulla and colleagues, 2020). They took 191 men from the U.S. NHANES national health survey, average age 45, scored each man's diet on a plant-based diet index (how much of what he ate came from plants) and a healthful plant-based diet index (how much came from whole plant foods rather than fries and white bread), and compared those scores with measured blood testosterone.

The result: neither index predicted testosterone. The only things that did were age and body weight. The authors' conclusion was one sentence long: plant-based food content in the diet is not associated with serum testosterone levels.

That's one study, and 191 men is not enormous. But it points the same direction as the older evidence, and it lines up with the biology. Testosterone is made from cholesterol, and your body makes all the cholesterol it needs whether or not you eat any. There is no animal-only ingredient in the recipe.

The soy question

Soy gets its own paragraph because the rumor is so persistent. Tofu, tempeh and edamame contain isoflavones, plant compounds that are structurally similar to estrogen, and from that fact a whole mythology has grown that soy “feminizes” men.

Multiple human trials and meta-analyses have not found that moderate soy intake reduces testosterone in men. The most cited is a 2010 meta-analysis in Fertility and Sterility pooling 15 placebo-controlled trials: no effect of soy protein or isoflavones on testosterone, free testosterone, or estrogen in men. The rumor traces back mostly to isolated case reports and to studies using isoflavone doses far beyond anything a person eating tofu a few times a week would consume.

So eat the tempeh. At roughly 16 grams of protein per 3-ounce serving it's one of the best plant proteins there is.

Two caveats that are real

Here is where honesty cuts the other way, because there are two things about a plant-based diet that can nudge testosterone down, and both are avoidable.

1. Going very low-fat

A 2021 systematic review and meta-analysis of intervention studies (Whittaker and Wu, Journal of Steroid Biochemistry and Molecular Biology) found that men switched to low-fat diets showed modest reductions in testosterone compared with men on higher-fat diets. That's a real finding at the low end. It is not evidence that piling extra fat on top of an adequate diet pushes testosterone higher; a 2024 analysis of more than 2,500 Finnish men found that once age and calories were accounted for, the type of fat made no independent difference at all.

The practical takeaway: a plant-based diet that is accidentally fat-starved (all rice, beans and steamed vegetables, no oil, no nuts) is the version that might cost you. Avocado, olive oil, nuts, seeds and tahini fix that without any drama.

2. Missing the deficiency-correction nutrients

Zinc and magnesium are required for testosterone synthesis, and correcting a shortfall helps. More than enough doesn't keep helping. Both are easy to get from plants (legumes, pumpkin seeds, whole grains, leafy greens, cashews) but easy to miss on a careless diet. Vitamin D is the other one to check with a blood test, since it's about sun more than food for everyone.

What actually moves testosterone

If diet quality mostly doesn't, what does? The levers with the strongest human evidence are not in the supplement aisle.

• Sleep. In a controlled study of healthy young men, one week of sleeping about five hours a night cut daytime testosterone by 10 to 15 percent, an effect comparable to 10 to 15 years of aging. No food does that in either direction.
• Body fat. Excess body fat converts testosterone to estrogen through the enzyme aromatase, and it was the strongest dietary-adjacent factor in the Miami study. A whole-food plant-based diet is one of the better-documented ways to lose it and keep it off.
• Chronic stress. Cortisol suppresses testosterone at the testes and at the brain signaling that controls them. This is the mechanism behind the one herb with a real, statistically significant testosterone result in a controlled trial, ashwagandha, whose best-documented action is lowering cortisol.
• Blood flow and fitness. Aerobic exercise improves the same nitric oxide pathway erections depend on, and resistance training supports lean mass. Both are covered in the book's fitness chapter.

The bottom line

Eating plant-based does not lower testosterone in the human studies that have looked. Soy does not either. What can lower it is eating too little fat, running short on a few minerals, carrying extra body fat, sleeping badly, and living stressed, and a well-built plant-based diet helps with at least two of those.

Green Game Chapter 3, “Testosterone, Naturally,” goes food by food and herb by herb through the claims, including the popular ones that don't hold up (cruciferous vegetables as “estrogen detox,” turmeric as a hormone modulator, tribulus, maca) and the handful that do.

Quick answers

Does a vegan diet lower testosterone?

The human data does not show it. A 2020 study of 191 U.S. men found no association between how plant-based a man's diet was and his blood testosterone; only age and body weight mattered.

Does soy lower testosterone in men?

No. A meta-analysis of 15 placebo-controlled trials found no effect of soy protein or isoflavones on men's testosterone or estrogen. The rumor comes from case reports and very high isoflavone doses far beyond normal eating.

Can a low-fat diet lower testosterone?

Modestly, yes. A 2021 meta-analysis found men switched to low-fat diets had somewhat lower testosterone. Adequate fat from nuts, seeds, avocado and olive oil avoids this; adding more fat beyond adequate does not raise testosterone further.

What lowers testosterone the most?

In controlled studies, short sleep is one of the largest and fastest: a week at about five hours a night cut testosterone 10 to 15 percent in healthy young men. Excess body fat and chronic stress are the other well-documented factors.