For many men diagnosed with testosterone deficiency, losing weight can help increase testosterone levels, say researchers, adding that, specifically a low-fat diet may be associated with a small but significant reduction in testosterone.
"We found that men who adhered to a fat restrictive diet had lower serum testosterone than men on a nonrestrictive diet," said study researcher Jake Fantus from University of Chicago in the US.
"However, the clinical significance of small differences in serum T across diets is unclear," Fantus added.
For the study, published in the Journal of Urology, the research team analysed data on more than 3,100 men from a nationwide health study (the National Health and Nutrition Examination Survey, or NHANES).
All participants had available data on diet and serum testosterone level.
Based on two-day diet history, 14.6 per cent of men met criteria for a low-fat diet, as defined by the American Heart Association (AHA).
Another 24.4 per cent of men followed a Mediterranean diet high in fruits, vegetables, and whole grains but low in animal protein and dairy products.
Only a few men met criteria for the AHA low-carbohydrate diet, so this group was excluded from the analysis.
The average serum testosterone level was 435.5 ng/dL (nanograms per deciliter).
According to the study, serum testosterone was lower in men on the two restrictive diets: average 411 ng/dL for those on a low-fat diet and 413 ng/dL for those on the Mediterranean diet.
The associations were adjusted for other factors that can affect testosterone, including age, body mass index, physical activity, and medical conditions.
After adjustment, the low-fat diet was significantly associated with reduced serum testosterone, although the Mediterranean diet was not.
Overall, 26.8 per cent of men had testosterone levels less than 300 ng/dL. Despite the difference in average testosterone levels, the proportion of men with low testosterone was similar across all diet groups.
The researchers noted that further studies will be needed to corroborate their findings, and to clarify the mechanism by which restrictive diets reduce testosterone.
But due to the difficulties of large-scale dietary studies, definitive trials are unlikely to be performed, they said.
"Therefore, our data represent a valuable approach towards answering this important question," the researchers concluded.
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