Is a High-Protein Diet Destroying Your Testosterone Levels?

Masculine stereotypes tend to suggest that the manliest diets are ones high in protein. Manly men love meat, happily down raw eggs à la Gaston from Beauty and the Beast and fuel up on protein shakes before hitting the gym to pump some iron. Contrary to these images of high-protein masculinity, however, some recent research suggests a high-protein diet might actually lower men’s testosterone levels.

The study, published in the journal Nutrition and Health and led by researcher Joe Whittaker of the University of Worcester in England, tested the testosterone levels of 309 men over the course of eight weeks. Subjects were fed a diet in which protein represented 35% of their caloric intake, including meat, fish and protein shakes. By the end of the study, subjects’ testosterone levels had dropped by 37%, representing a sufficiently low level to constitute medical hypogonadism. Subjects also began to display symptoms of low testosterone, including fatigue, erectile dysfunction, depression and muscle weakness, Whittaker told Insider.

While a relatively small study, the significant decline in testosterone researchers observed certainly has some implications for the popular high-protein, low-carb diets that have taken over in recent years. According to Whittaker, an average person’s diet is only about 17% protein, meaning a casual consumer of meat and eggs needn’t worry. But someone following a high-protein diet should be careful, the researcher said in a statement.

While the most severe drops in testosterone were observed among men whose protein intake was 35% or higher, Whittaker warns that even lower levels of protein consumption can have an adverse effect on testosterone, suggesting any high-protein dieters limit their protein intake to “no more than 25 percent.”

In addition to more immediate risks like erectile dysfunction and fatigue, low testosterone is also linked to long-term health consequences such as cardiovascular disease, diabetes and Alzheimer’s. Moreover, researchers also noted that high-protein, low-carb diets led to higher levels of cortisol, aka the stress hormone. Elevated levels of cortisol can suppress the immune system and increase risk of illness and infection.

So while a high-protein diet may seem like the healthiest way to stay strong and lean, it seems too much protein can wreak havoc on your health. As always, balance is key, so if you want to keep your testosterone levels in check, maybe throw in a carb every now and then and lay off the raw eggs, Rocky.