A Finnish study of more than 2,500 men has linked higher animal protein intake to slightly lower testosterone levels, while plant protein showed the opposite association.
The University of Eastern Finland research, published in the International Journal of Food Sciences and Nutrition, examined 2,546 Finnish men aged 42 to 60. Researchers compared four-day food records collected between 1984 and 1989 with blood samples measuring testosterone and sex hormone-binding globulin, a protein that carries sex hormones through the bloodstream.
Participants were divided into four groups based on protein consumption. Those with the highest animal protein intake showed average testosterone levels 1.2 nanomoles per liter lower than men with the lowest intake. Men eating the most plant protein registered levels 1.1 nanomoles per liter higher than those consuming the least.
The team also accounted for age, body mass index, other dietary habits, lifestyle factors and overall health in their analysis. A more detailed breakdown revealed dairy protein was associated with both lower testosterone and lower levels of the hormone-carrying protein. Protein from vegetables and other plant foods, excluding cereal products, correlated with higher testosterone.
Meat protein presented a more nuanced finding: it was tied to lower levels of sex hormone-binding globulin, but not to lower total testosterone. The researchers cautioned that the overall animal-protein result should not be read as evidence that meat consumption alone suppresses testosterone production.
The study’s design carries important limitations. Researchers observed existing diets and hormone levels rather than assigning participants a specific diet and tracking changes over time. The findings show correlation, not causation.
Doctoral researcher Miika Wynne-Ellis, from the University of Eastern Finland, said: “Although the observed differences in testosterone concentrations were statistically significant, they were relatively small. Based on this study, it is not possible to infer whether these differences have implications for health.”
The data emerged from the university’s ongoing Kuopio Ischaemic Heart Disease Risk Factor Study. While the food records date to the 1980s, the analysis paired reported protein intake with contemporaneous testosterone measurements.
The researchers noted that other dietary components, or individual variations in how bodies process food, could explain the observed patterns. The findings cannot determine whether protein sources influence testosterone production itself or merely how the hormone functions in the body.
Testosterone contributes to men’s sexual function, muscle maintenance and bone health. Levels naturally fluctuate based on age, excess weight and lifestyle choices, meaning diet represents just one of multiple potential factors.
The study did not demonstrate that altering diet alone would change testosterone levels. Further investigation would be needed to establish whether shifting the balance between animal and plant protein produces meaningful effects on men’s hormones or overall health.