Protein gets plenty of attention for its role in building muscle and maintaining strength. But could choosing chicken over beans, or yogurt over tofu, make a difference in men's testosterone levels?
A new study suggests protein sources may matter, although the findings are far from a reason to overhaul your diet. Researchers found that middle-aged men who ate more animal protein tended to have slightly lower testosterone levels, while those who ate more plant protein tended to have higher levels. The differences were small, however, and the study couldn't determine whether protein choices were responsible.
Published in the International Journal of Food Sciences and Nutrition, the research examined dietary records and blood samples from 2,546 Finnish men ages 42 to 60. Researchers compared how much protein the men consumed from different foods with their testosterone levels, accounting for factors such as age, body weight, physical activity and other dietary habits.
Men who consumed the most animal protein had testosterone levels averaging about 6% lower than those who consumed the least. The opposite pattern appeared with plant protein, with levels roughly 5% higher among men who consumed the most.
But not all animal proteins showed the same relationship. Higher dairy protein intake was associated with lower testosterone levels, particularly protein from fermented dairy products. Meat, fish and eggs showed no significant associations with testosterone after researchers accounted for other factors.
Among plant foods, protein from sources other than grains, including vegetables, beans, nuts and seeds, was associated with somewhat higher testosterone levels. Protein from grains alone showed no significant association.
So does this mean men should swap their steaks for lentils to improve testosterone levels? Not necessarily.
The researchers also looked at what might happen if men replaced some animal protein with plant protein while keeping their calorie intake the same. Most of those statistical comparisons found no significant differences in testosterone levels. And because this was an observational study, researchers couldn't establish that changing protein sources would change hormone levels.
There's another important distinction. The study measured total testosterone, which includes hormone carried by proteins in the blood. Researchers also examined estimated levels of free testosterone, the portion that isn't attached to those proteins. Those results were less consistent, suggesting that differences in total testosterone don't necessarily reflect changes in how much hormone the body produces or uses.
That matters because higher testosterone readings don't automatically mean better muscle strength, sexual function or overall health. The study didn't examine whether the differences in hormone levels had any effects on those outcomes.
The findings also come with some limitations. The dietary information was collected between 1984 and 1989, when eating habits in Finland differed from those of modern Americans. Diet was recorded over just four days, and testosterone was measured only once. Other differences in the men's lifestyles or health could also help explain the results.
Still, the research adds another perspective to the ongoing conversation about whether protein sources matter as much as the amount we eat. Meat, dairy, beans and other protein-rich foods provide different combinations of nutrients, and their effects on health may extend well beyond their protein content.
Previous research has also raised questions about how dietary habits relate to testosterone measurements, reinforcing the importance of distinguishing changes in blood levels from meaningful improvements in health.
For now, the Finnish findings offer an interesting clue about how protein choices and hormone levels might be connected. They don't establish that eating more plant protein will boost testosterone or that men need to avoid animal protein to maintain healthy hormone levels.
The study received no specific funding from public, commercial or nonprofit organizations.