A study of more than 2,500 men in Finland found that higher plant-protein intake was associated with slightly higher total testosterone. The results also challenge the popular idea that eating more meat necessarily raises the hormone.
Researchers analyzed four-day food diaries and morning blood samples collected from men aged 42 to 60 in eastern Finland between 1984 and 1989. After adjusting for factors including age, smoking, physical activity and body mass index, men in the highest plant-protein group had an average total testosterone level of 21.5 nanomoles per liter, compared with 20.4 in the lowest group.
The pattern was reversed for animal protein: the highest-intake group averaged 20.3 nanomoles per liter, while the lowest averaged 21.5. However, when individual foods were considered, meat, fish and eggs showed no clear association with testosterone. Dairy protein was linked to lower total testosterone.
What the findings do--and don't--show
The study identifies associations, not cause and effect. It also measured total testosterone, which includes hormone bound to proteins such as sex hormone-binding globulin (SHBG). Since SHBG levels also varied with protein intake, the total testosterone figures may not reflect how much hormone is freely available to the body. Results for free testosterone were less consistent.
Researchers said the observed differences were modest and their health significance is not established. The study, published in the International Journal of Food Sciences and Nutrition, does not show that changing protein sources will alter testosterone levels.
As nutrition research grows more precise, studies that distinguish between total and biologically available hormones may help clarify how dietary patterns relate to health.
