Does Plant Protein Increase Testosterone?
Middle-aged Finnish men who ate more plant protein had modestly higher testosterone, and those who ate more animal protein had modestly lower levels. Whether switching your own protein would raise yours is still unknown, because the study compared different men at a single point in time. Trials that gave men soy protein found no dependable boost. They are reassuring, though: the overall soy evidence doesn't show a consistent testosterone drop.
For years, the question of protein and testosterone mostly meant one thing: does soy lower it? Short trials of soy supplements in young or athletic men mostly found no consistent effect. A new analysis from eastern Finland turns the question around. It looks at the protein middle-aged men habitually eat, and it links plant protein to higher testosterone and animal protein to lower.
What 2,546 Finnish men's diets showed
The data come from the Kuopio Ischaemic Heart Disease Risk Factor Study, which enrolled men aged 42 to 60 in eastern Finland and had them keep four-day food records between 1984 and 1989, alongside blood tests for hormones. After adjusting for age, BMI, and other dietary and lifestyle factors, men in the top quarter of plant protein intake had total testosterone about 1.1 nmol/L higher than men in the bottom quarter. Men in the top quarter of animal protein had levels about 1.2 nmol/L lower. These are two separate comparisons, so they can't be added together into an expected gain from swapping one protein for the other.
The food details complicate a simple meat-versus-plants story. Dairy protein was linked to lower testosterone and SHBG, while meat protein was linked only to lower SHBG, and not to testosterone itself. On the plant side, protein from vegetables and other non-cereal sources carried the link with higher testosterone.
Each of these findings is a snapshot of different men at one moment. Men who ate more vegetables in 1980s Finland may have differed in other ways too, and statistical adjustment can't remove all of that; the authors say the pattern could reflect other parts of the diet or metabolic factors. The lead author called the differences relatively small, and the study can't say whether they matter for health.
Why higher total testosterone isn't enough
Much of the testosterone in your blood travels attached to sex hormone-binding globulin (SHBG), and the bound share isn't freely available to tissues. In the Finnish men, SHBG moved in step with testosterone: about 3 nmol/L higher in the top versus bottom plant-protein quarter and about 3 nmol/L lower in the equivalent animal-protein comparison. With SHBG also differing, a higher total doesn't by itself mean more usable hormone.
The study's abstract reports that free testosterone was lower in men with a higher ratio of animal to plant protein and higher in men eating more non-grain plant protein, though it doesn't give the size of those differences. The study doesn't establish improvements in libido, erections, energy, fertility, or quality of life, which are the outcomes that would make a hormone difference worth chasing.
What happens when men are given plant protein
The way to learn whether protein source changes hormones is to assign men to eat one kind or the other. Those trials exist, though the ones below don't test what the Finnish data suggest: a whole-food shift from animal to plant protein in middle-aged men.
| Evidence | What was compared | Testosterone finding | What it settles |
|---|---|---|---|
| 2026 Finnish cross-sectional study | Men eating the most versus least plant or animal protein in their usual diet | Higher with more plant protein, lower with more animal protein | Raises the question; can't show cause and effect |
| 2016 randomized trial | Soy-dairy blend, whey, or placebo for 12 weeks in 68 young men doing resistance training | No significant difference between groups | No boost or suppression detected from the blend during resistance training |
| 2023 systematic review | Randomized trials of soy supplements in active people and athletes | Inconsistent effects | No dependable rise or fall from soy supplements |
One more trial speaks to men whose levels are already low. In men with type 2 diabetes and low testosterone, three months of soy protein, with or without isoflavones, produced no significant change in total or free testosterone. Taken together, the controlled evidence is fairly reassuring that soy doesn't consistently lower testosterone, and it gives no reliable sign that it pushes it up. It's also narrow evidence: mostly supplements, mostly short, and mostly in young or selected men.
If low testosterone is why you're asking
If symptoms are behind the question, the more useful first step is finding out where your levels stand. Testosterone and SHBG are straightforward to check yourself. European urology guidelines call for a fasting blood draw between 7 and 10 a.m., with low results confirmed on at least two separate occasions, and a diagnosis of late-onset hypogonadism needs both compatible symptoms and repeatedly low results. When SHBG runs unusually high or low, calculated free testosterone gives a better read than the total alone, and the same guidelines advise against direct free-testosterone immunoassays because they're inaccurate. A confirmed low result alongside symptoms is worth taking to a clinician, since the possible causes and treatments depend on your history.
Body weight has stronger support than protein source. For overweight or obese men with low testosterone, the guidelines put weight reduction and lifestyle change first, and a year-long trial in overweight and obese men found testosterone rose as they lost weight, whether they followed a higher-protein or higher-carbohydrate diet. If you carry extra weight, that is the dietary change with the clearest hormonal evidence behind it.
Eating more beans, vegetables, and other plant protein is a reasonable choice. A claim that it treats symptomatic low testosterone would need randomized trials that swap whole-food animal protein for plant protein while holding calories, total protein, and weight steady, run in middle-aged men with low levels, and showing that free testosterone and symptoms both improve. Until then, the Finnish result is a lead for researchers, and protein source shouldn't stand in for treating a confirmed deficiency.