University of Eastern Finland study has linked protein sources to differences in testosterone levels

Researchers at the University of Eastern Finland have found that higher plant protein intake was associated with higher total testosterone concentrations in middle-aged men, while higher animal protein intake was associated with lower concentrations. The study did not establish whether protein sources caused the differences or whether they affected health.

• Researchers analyzed dietary records and hormone measurements from 2,546 Finnish men.
• Plant and animal proteins showed opposite associations with total testosterone.
• The findings did not establish causation or health benefits.

Published in the International Journal of Food Sciences and Nutrition, the research examined data from men aged 42-60 who participated in the Kuopio Ischaemic Heart Disease Risk Factor Study. Although the paper was published online on September 9, 2026, the dietary records and blood samples used in the analysis were collected between 1984 and 1989.

Men in the highest quarter of animal protein intake had adjusted total testosterone concentrations averaging 1.2 nanomoles per liter lower than those in the lowest quarter. For plant protein, the relationship ran in the opposite direction: concentrations were 1.1 nanomoles per liter higher among men with the highest intake.

Similar patterns were recorded for sex hormone-binding globulin, or SHBG, a protein that binds testosterone in the blood. SHBG concentrations were approximately 3 nanomoles per liter lower in the highest animal protein group and 3 nanomoles per liter higher in the highest plant protein group.

“The study cannot establish whether these differences have implications for health,” said Miika Wynne-Ellis, Doctoral Researcher at the University of Eastern Finland, in the university’s announcement. He described the observed differences as relatively small despite their statistical significance.
University of Eastern Finland

Participants recorded everything they ate over four days, covering three weekdays and one weekend day. Nutritionists checked the completed records with participants, using portion-size illustrations and household measures to improve the accuracy of the information.

The researchers adjusted their analyses for age, energy intake, body mass index, smoking, alcohol consumption, physical activity, education and existing cardiovascular disease or diabetes. They also accounted for several dietary factors, including fiber, fruit and vegetable intake, and different types of fat.

More detailed analysis showed that the findings varied between individual protein sources. Higher total dairy and fermented dairy protein intakes were associated with lower total testosterone and SHBG concentrations. Meat protein was associated with lower SHBG, but not with a statistically significant difference in total testosterone.

Fish and egg proteins showed no statistically significant associations with either measure after adjustment.

Among plant sources, protein from foods other than grains was associated with higher total testosterone. This category included vegetables, legumes, seeds, nuts, fruit, berries and mushrooms. Grain protein did not show a statistically significant relationship with total testosterone.

The results for calculated free testosterone were less consistent. Free testosterone was not directly measured, but estimated from total testosterone and SHBG. The researchers therefore treated those analyses as supplementary.

A higher ratio of animal to plant protein was associated with lower calculated free testosterone, while non-grain plant protein was associated with higher concentrations. Most individual protein categories showed no statistically significant relationship.

The authors also modeled what might happen when plant protein replaced an equivalent amount of energy from animal protein. Most of these substitution estimates were not statistically significant, including those for total and calculated free testosterone.

Replacing 2% of dietary energy from low-fat dairy protein with plant protein was associated with higher SHBG. However, the researchers cautioned against placing too much weight on an individual finding given the number of comparisons undertaken.

Interpreting total testosterone also requires attention to its relationship with SHBG. Lower concentrations of the binding protein can contribute to lower measured total testosterone without necessarily indicating reduced testosterone production or biological activity.

The study did not measure those processes directly or assess clinical outcomes. Its cross-sectional design also meant diet and hormone concentrations were examined at the same stage, preventing conclusions about which came first.

Other limitations included reliance on a single hormone measurement and food records covering only four days. The authors acknowledged that differences in lifestyle, metabolism or overall dietary patterns could still help explain the associations despite statistical adjustments.

The participants were white men from eastern Finland, which also limits how confidently the findings can be applied to other populations. The authors called for longitudinal research and controlled dietary trials, with more direct measurements of testosterone metabolism, to establish whether the observed associations have physiological significance.

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