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Low Fat Diets Hurt Men, Reduce Testosterone

Testosterone deficiency occurs when a male’s body does not produce enough serum testosterone. Though exercise and weight loss can combat this deficiency, a study published in The Journal of Urology suggests that the type of diet matters.

The new study finds that men following a low-fat diet may have lower serum testosterone levels than those with different diets.

Scientists have linked a deficiency of this hormone to a variety of health issues, including:

• reduced bone mass
• erectile dysfunction
• diminished energy and sex drive
• sleeping difficulties
• mood swings
• reduced semen
• increased body fat
• hair loss
• hot flashes
• reduced testicle size
• changes in cognition

In addition, there is evidence of a possible connection between low testosterone and chronic conditions such as high blood pressure and type 2 diabetes. Low serum testosterone levels may also contribute to certain aggressive types of cancer.

While in some cases the deficiency results from an identifiable cause, its source often remains unknown.

While weight reduction can lead to an increase in testosterone levels, in some cases it has the opposite effect. Precisely why losing weight can help resolve low serum testosterone is unclear.

Hoping to shed light on this issue, the researchers behind the recent study have investigated the potential influence of fat intake on testosterone. They write:

“While dieting for weight loss will clearly help optimize cardiovascular health, with corresponding reductions in lipid profiles, the effect of diet on [testosterone] is not well established.”

The authors of the study began with the intention of assessing the effects of four diets on testosterone:

• a low-fat diet, as defined by the American Heart Association (AHA)
• a Mediterranean diet, which involves a high intake of fruits, vegetables, and whole grains and minimal intake of animal protein and dairy products, and thus animal fats
• a low-carbohydrate diet, as defined by the AHA
• a nonrestrictive diet

The researchers analyzed data sets from the National Health and Nutrition Examination Survey. The relevant data had been collected during three periods: 1999–2000, 2003–2004, and 2011–2012. For the survey, men aged 18–80 had submitted a 2-day dietary history and undergone serum testosterone testing.

Overall, the researchers analyzed data from 3,128 men. While 457 men from this group had followed a low-fat diet and 764 had followed a Mediterranean diet, only two had followed a low-carbohydrate diet. The researchers, therefore, excluded this diet from their analysis.

“We found that men who adhered to a fat-restrictive diet had lower serum testosterone than men on a nonrestrictive diet,” says lead author Dr. Jake Fantus, of the University of Chicago Medical Center, in Illinois.

The mean serum testosterone level for the entire cohort was roughly 435.5 nanograms per deciliter (ng/dl). Men on a low-fat diet had an average serum testosterone level of 411 ng/dl, and those on a Mediterranean diet had an average of 413 ng/dl.

After adjusting for factors that can influence testosterone, such as age, physical activity, and body mass index, the researchers determined that the Mediterranean diet did not cause a significant reduction in testosterone, whereas the reduction associated with a low-fat diet was small but significant.

The study admits that “The clinical significance of small differences in serum [testosterone] across diets is unclear,” and acknowledges that “Future prospective research is required to corroborate these findings and elucidate the mechanisms by which restrictive dieting may affect serum testosterone.”

Meanwhile, the implications of the study’s findings may vary depending on other health indicators.

The authors conclude that men with obesity may view a potential slight reduction in serum testosterone to be a relatively minor consideration in comparison with the potential benefits of a low-fat diet.

Men with a testosterone deficiency who are maintaining a healthy weight, however, may wish to consider an alternate diet, if the findings of the current study are supported by more research.