Carried out by researchers at University of Chicago Medicine, Northwestern University Feinberg School of Medicine, and Chicago NorthShore University HealthSystem, the new investigation looked at 3,128 men aged 18 to 80 who were taking part in a nationwide health study, the National Health and Nutrition Examination Survey, or NHANES.
All participants had provided data on their diet, with 14.6 percent of the men meeting the criteria for following a low-fat diet, as defined by the American Heart Association (AHA). Of the rest, 24.4 percent followed a Mediterranean diet, which is high in fruits, vegetables, and whole grains and low in animal protein and dairy products. A few men who followed a low-carb diet were excluded from the study.
The men also provided blood samples to analyze their serum testosterone levels.
The findings, published in The Journal of Urology, Official Journal of the American Urological Association (AUA), showed that the average serum testosterone level was 435.5 ng/dL (nanograms per deciliter). However, serum testosterone levels were lower in the men following the two “restrictive diets”: the average level was 411 ng/dL for the men on a low-fat diet and 413 ng/dL for those on the Mediterranean diet.
After taking into account factors that can affect testosterone, such as age, body mass index, and physical activity, following a low-fat diet was still significantly associated with reduced serum testosterone, although the Mediterranean diet was not.
“We found that men who adhered to a fat restrictive diet had lower serum testosterone than men on a nonrestrictive diet,” according to the report by Jake Fantus, MD, “[h]owever, the clinical significance of small differences in serum T across diets is unclear,” added the researchers.
The researchers note that for men diagnosed with testosterone deficiency, losing weight can help increase testosterone levels. However, the new findings suggest that certain diets, specifically a low-fat diet, may actually be linked with a small but significant reduction in testosterone. The team explain that because testosterone is a steroid hormone derived from cholesterol, changes in fat intake could change testosterone levels.
The team add that further studies are now needed to replicate the findings and that it is still unclear which diet is best for men with testosterone deficiency, although they add that for overweight or obese men the health benefits of a low-fat diet will probably far exceed the small reduction in serum testosterone. For men who are not overweight, they say, avoiding a low-fat diet “may be a reasonable component” of a multifaceted approach to increasing serum testosterone.