Study of 2,546 Finnish men links animal protein to lower testosterone and plant protein to higher levels
A cross-sectional study from the University of Eastern Finland found small, opposite links of animal and plant protein with testosterone and SHBG. Health effects are unclear.
Researchers at the University of Eastern Finland examined the link between dietary protein and sex hormones in 2,546 men aged 42–60 living in eastern Finland. The results were published in the International Journal of Food Sciences and Nutrition. Higher total and animal protein intakes, and a higher animal-to-plant protein ratio, were associated with lower total testosterone and sex hormone-binding globulin (SHBG), whereas plant protein intake was positively associated with both doi.org
International Journal of Food Sciences and Nutritiondoi.orgOpen source ↗.
The data came from the university's ongoing Kuopio Ischaemic Heart Disease Risk Factor Study. Diets were assessed with 4-day food records collected between 1984 and 1989, and total testosterone and SHBG were measured in blood samples. SHBG is a protein that binds sex hormones and influences the concentration of total testosterone in blood. The models were adjusted for age, body mass index and several other dietary, lifestyle and health factors.
Differences between protein quartiles
The men were divided into four groups by protein intake. In the highest versus the lowest animal protein quartile, total testosterone was 1.2 nmol/L lower (95% CI: 0.37–2.03) and SHBG was 3.0 nmol/L lower (95% CI: 1.34–4.66) doi.org
International Journal of Food Sciences and Nutritiondoi.orgOpen source ↗. In the highest versus the lowest plant protein quartile, total testosterone was 1.1 nmol/L higher (95% CI: 0.34–1.93) and SHBG was 3.0 nmol/L higher (95% CI: 1.06–4.94)
doi.org
International Journal of Food Sciences and Nutritiondoi.orgOpen source ↗.
Free testosterone was inversely associated with the animal-to-plant protein ratio and positively associated with protein from non-grain plant sources doi.org
International Journal of Food Sciences and Nutritiondoi.orgOpen source ↗.
Protein sources and limitations
By food group, higher dairy protein intake was associated with lower total testosterone and SHBG. Meat protein intake was associated with lower SHBG but not with total testosterone. Among plant foods, protein from vegetables and from sources other than cereal products was associated with higher total testosterone.
"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," said doctoral researcher Miika Wynne-Ellis.
The study is cross-sectional, so it cannot establish that eating particular proteins caused the hormonal differences. It also cannot show whether the protein source changes testosterone production or the way the hormone acts in the body. Even after adjustment, other features of the diet or metabolic factors may partly explain the associations. Higher testosterone is not necessarily healthier, and the authors do not claim that either protein source improves hormone function.
