Animal vs. plant protein reveals a surprising testosterone divide

The findings, published in the International Journal of Food Sciences and Nutrition, suggest that protein sources may be associated with male hormone levels in different ways. However, the researchers caution that the differences were relatively small and that the results do not establish whether protein intake directly influences testosterone.

Testosterone is an essential male sex hormone that helps maintain muscle mass, bone health, and sexual function. Although age, excess body weight, and lifestyle habits are known to influence testosterone levels, scientists have conducted relatively little research into how diet, especially protein consumption, might be associated with this hormone.

Study of More Than 2,500 Men Reveals Contrasting Protein Patterns

To investigate the relationship, researchers analyzed information from 2,546 men between the ages of 42 and 60 who lived in eastern Finland. The participants were part of the ongoing Kuopio Ischaemic Heart Disease Risk Factor Study, a research project conducted at the University of Eastern Finland.

Between 1984 and 1989, the men recorded everything they ate over four days, allowing researchers to evaluate their dietary habits and protein sources. Blood samples were also collected to measure total testosterone and sex hormone-binding globulin (SHBG), a protein that helps regulate the amount of testosterone circulating in the bloodstream.

The researchers then divided the participants into four groups based on their protein consumption. A clear contrast emerged when they compared the men with the highest and lowest intakes of animal and plant protein.

Men who consumed the most animal protein had average total testosterone concentrations 1.2 nmol/l lower than those who consumed the least. Plant protein showed the opposite pattern, with men in the highest intake group having testosterone concentrations 1.1 nmol/l higher than those in the lowest group.

Similar relationships were observed for SHBG concentrations. The associations remained after the researchers accounted for age, body mass index, and several other factors related to diet, lifestyle, and health.

Dairy and Plant Proteins Show Different Testosterone Links

A closer examination of individual protein sources revealed additional differences. Higher consumption of protein from dairy products was associated with lower concentrations of both total testosterone and SHBG.

Meanwhile, men who obtained more plant protein from vegetables and sources other than cereal products tended to have higher total testosterone concentrations.

Meat protein showed a somewhat different relationship. Although greater meat protein intake was linked to lower SHBG concentrations, researchers did not find a corresponding association with total testosterone levels.

These distinctions suggest that the relationship between dietary protein and male hormones may vary depending on where the protein comes from, rather than simply how much protein a person consumes.

What the Findings Mean for Men's Health

Despite the contrasting patterns, the researchers emphasize that the observed testosterone differences were modest. It is also unknown whether changes of this size have any meaningful consequences for health.

"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," says Doctoral Researcher Miika Wynne-Ellis from the University of Eastern Finland.

An important limitation is that the research was cross-sectional, meaning dietary intake and hormone measurements were examined without tracking how changes in protein consumption affected testosterone over time. As a result, the findings cannot establish a cause-and-effect relationship.

Other dietary characteristics or metabolic factors could help explain the associations. The researchers also cannot determine whether eating different types of protein influences testosterone production or changes how the hormone functions in the body.

For now, the findings highlight an interesting connection between protein sources and testosterone levels, while leaving open the question of whether changing protein choices could have any direct effect on male hormone health.