Study links animal protein to lower testosterone in men, plant protein to higher
A University of Eastern Finland study found that men eating more animal protein had slightly lower testosterone, while those eating more plant protein had higher levels. The researchers stress the differences are small and causation is not shown.
Researchers at the University of Eastern Finland, analysing dietary data from more than 2,500 men, have found a link between the source of dietary protein and blood testosterone levels. Men who ate more animal protein tended to have lower testosterone, while those who consumed more plant protein generally had higher levels. The results were published in the International Journal of Food Sciences and Nutrition. The authors caution that the differences were small and that it remains unknown whether protein intake directly affects the hormone.
Testosterone is a key male sex hormone that helps maintain muscle mass, bone health and sexual function. Age, excess weight and lifestyle are known to affect its levels, but relatively little research has examined the role of diet, and protein in particular.
How the study worked
The analysis covered 2,546 men aged 42 to 60 living in eastern Finland. They were participants in the Kuopio Ischaemic Heart Disease Risk Factor Study, run by the university. Between 1984 and 1989 the men recorded everything they ate over four days. Blood samples were taken to measure total testosterone and sex hormone-binding globulin (SHBG), a protein that helps regulate how much testosterone circulates in the blood. Participants were divided into four groups by protein intake.
Findings
Men with the highest animal protein intake had average total testosterone 1.2 nmol/l lower than those with the lowest intake. For plant protein the pattern was reversed: the top intake group had levels 1.1 nmol/l higher than the bottom group. Similar relationships appeared for SHBG, and they held after adjusting for age, body mass index and other diet, lifestyle and health factors.
Protein from dairy was linked to lower total testosterone and SHBG. Plant protein from vegetables and non-cereal sources was associated with higher total testosterone. Meat protein was linked to lower SHBG but not to total testosterone.
Limitations
"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 of the University of Eastern Finland. The study was cross-sectional, so it cannot establish cause and effect.
