The key facts

  • Men with the highest animal protein intake had testosterone levels on average 1.2 nmol/l lower than the group with the lowest intake
  • For plant protein, the association was reversed: the difference was 1.1 nmol/l in favor of the group with the highest intake
  • The study is cross-sectional and does not prove that changing the type of protein alters hormone levels

What the data on 2,546 men showed

Researchers at the University of Eastern Finland analyzed data on men aged 42 to 60 living in eastern Finland. Their diet was recorded over four days in 1984–1989, and blood samples were used to measure total testosterone and sex hormone-binding globulin — a protein that affects the concentration of testosterone in the blood. This was reported by euronews citing the publication and a statement from the university.

Different protein sources — different associations

Among men in the group with the highest intake of animal protein, the average concentration of total testosterone was 1.2 nanomoles per liter lower than in the group with the lowest intake. For plant protein, the association was the opposite: in the group with the highest intake, the figure was 1.1 nmol/l higher. In more detail: protein from dairy products was associated with lower concentrations of both total testosterone and sex hormone-binding globulin; protein from meat was associated with a lower concentration of globulin but not with total testosterone levels. The association with higher total testosterone was shown by plant protein from vegetables and sources other than grain products. The analyses accounted for age, body mass index, and a number of other factors related to diet, lifestyle, and health.

Limitations: an association, not causation

The study was conducted as a cross-sectional analysis, meaning it identified associations rather than cause-and-effect relationships: it does not prove that animal protein lowers testosterone or that switching to a plant-based diet raises it. Hormone levels change with age, body weight, and other factors, which makes it difficult to isolate the contribution of any single dietary component. “Although the observed differences in testosterone concentration were statistically significant, they were relatively small”, noted doctoral researcher Miika Win-Elis in a statement on the results.