A new study of more than 2,500 Finnish men, published in the International Journal of Food Sciences and Nutrition, found that men who got the most protein from plants averaged about 5% more total testosterone than low-plant-protein peers.

Between 1984 and 1989, men aged 42 to 60 in eastern Finland kept four-day food diaries and gave fasting morning blood samples; decades later, researchers matched those records to hormone levels.

After adjusting for age, smoking, physical activity and BMI, the highest plant-protein group averaged 21.5 nanomoles per liter versus 20.4 in the lowest, ZME Science reports.

Protein marketing has long equated meat and shakes with masculinity, but the data ran the other way: men in the highest quarter for animal protein averaged 20.3 nmol/L, compared with 21.5 in the lowest quarter, while men who ate the most meat showed about the same testosterone as those who ate the least, according to ZME Science.

When researchers broke animal protein into individual foods, dairy protein — particularly fermented products — was the item associated with lower testosterone, while meat overall, unprocessed red meat, processed red meat, fish and eggs showed no clear link.

ZME Science emphasizes an important caveat: most testosterone travels attached to a protein called SHBG, and only a small fraction circulates freely enough to affect tissues.

In the study, higher plant protein intake was associated with higher SHBG, while higher animal protein went with lower SHBG — meaning the plant-protein group's higher total testosterone could simply be more hormone locked in its bound form.

When the researchers examined free testosterone, the results were much less consistent, echoing a 2000 British Journal of Cancer study in which vegans had higher total testosterone and SHBG but essentially no difference in free levels.

The findings also challenge the persistent gym-floor myth that soy lowers men's testosterone. ZME Science notes this confirms earlier work: a 2021 analysis of 38 clinical studies found no significant effect of soy protein or isoflavones on men's testosterone or estrogen levels.

The researchers also modeled swapping animal protein for plant protein directly, and most substitutions showed no statistically significant effect on testosterone or SHBG — so there is no compelling reason to switch protein sources purely for hormone reasons, the outlet reports.

The protein study lands amid an unusually active stretch for nutrition-science headlines.

Preliminary American Heart Association research presented this week found caffeinated energy drinks and stimulant supplements appeared disproportionately in FDA reports of cardiac arrest and heart attacks, especially among adults 18 to 34, NBC News reports.

The AHA's 2026 scientific statement on caffeine, cited in the association's own release, holds that up to 400 mg of caffeine daily is generally safe for most adults — a reminder that nutrition guidance keeps shifting on both what to drink and what to eat.

The authors themselves urge restraint.

"Although the observed differences in testosterone concentrations were statistically significant, they were relatively small. The study cannot establish whether these differences have implications for health," doctoral researcher Miika Wynne-Ellis of the University of Eastern Finland said in a university statement quoted by ZME Science.

The paper is published in the International Journal of Food Sciences and Nutrition, and the practical takeaway is modest: protein choice does not need to change for hormone's sake, but the assumption that more animal protein means more testosterone has lost its scientific footing.