Plant and animal proteins show opposite effects on testosterone levels

Higher animal protein intake was associated with lower blood testosterone levels, while higher plant protein intake was associated with higher levels, according to a new study from the University of Eastern Finland. The findings were published in the International Journal of Food Sciences and Nutrition.

Testosterone is a key male sex hormone and is important for, among other things, muscles, bones and sexual function. Testosterone levels are influenced by factors such as age, overweight and lifestyle, but relatively few studies have examined the associations between testosterone levels and diet, particularly protein intake.

The new findings are based on data from the ongoing Kuopio Ischaemic Heart Disease Risk Factor Study at the University of Eastern Finland. The study included 2,546 men aged 42-60 years and living in eastern Finland. Their dietary intake was assessed using four-day food records between 1984 and 1989, and concentrations of total testosterone and sex hormone-binding globulin (SHBG) were measured in blood samples. SHBG influences total testosterone concentrations in the blood.

When the men were divided into four groups according to their protein intake, those with the highest animal protein intake had total testosterone concentrations that were, on average, 1.2 nmol/l lower than those of men with the lowest intake. The opposite association was observed for plant protein: those with the highest intake had concentrations 1.1 nmol/l higher than those of men with the lowest intake. Similar associations were also observed for SHBG concentrations. The analyses accounted for the participants' age and body mass index, as well as several other dietary, lifestyle and health-related factors.

More detailed analyses showed that higher dairy protein intake was associated with lower total testosterone and SHBG concentrations. Higher intake of plant protein from vegetables and sources other than cereal products was, in turn, associated with higher total testosterone concentrations. Meat protein intake was associated with lower SHBG concentrations but not with total testosterone concentrations.

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."

Miika Wynne-Ellis, Doctoral Researcher, University of Eastern Finland

The study was cross-sectional, so the findings do not establish a causal relationship. The associations may also be related to other aspects of the diet or to metabolic factors. Nor can the findings establish whether consuming different protein sources affects testosterone production or its effects in the body.