Lowest testosterone levels with low-fat vegetarian diets
Overall, on average, the men’s total testosterone was 475 mg/dL when they were consuming a low-fat diet and 532 mg/dL when they were consuming a high-fat diet.
However, the South African men had higher testosterone levels when they consumed a low-fat diet. This suggests that “men with European ancestry may experience a greater decrease in testosterone in response to a low-fat diet,” the researchers wrote.
The decrease in total testosterone in the low-fat versus high-fat diet was largest (26%) in the two studies of men who consumed a vegetarian diet (Hill 1979 and Hill 1980). These diets may have been low in zinc, since a marginal zinc deficiency has been shown to decrease total testosterone, Mr. Whittaker and Mr. Wu speculated.
The meta-analysis also showed that levels of free testosterone, urinary testosterone, and dihydrotestosterone declined during the low-fat diet, whereas levels of luteinizing hormone or sex hormone binding globulin were similar with both diets.
Men with low testosterone and overweight, obesity
What nutritional advice should practitioners give to men who have low testosterone and overweight/obesity?
“If you are very overweight, losing weight is going to dramatically improve your testosterone,” Mr. Whittaker said.
However, proponents of various diets are often in stark disagreement about the merits of a low-fat versus low-carbohydrate diet to lose weight.
“In general,” he continued, “the literature shows low-carb (high-fat) diets are better for weight loss [although many will disagree with that statement].”
Although nutrition guidelines have stressed the importance of limiting fat intake, fat in the diet is also associated with lower triglyceride levels and blood pressure and higher HDL cholesterol levels, and now in this study, higher testosterone levels.
More research needed
The researchers acknowledge study limitations: The meta-analysis included just a few small studies with heterogeneous designs and findings, and there was possible bias from confounding variables.
“Ideally, we would like to see a few more studies to confirm our results,” Mr. Whittaker said in the statement. “However, these studies may never come; normally researchers want to find new results, not replicate old ones. In the meantime, men with low testosterone would be wise to avoid low-fat diets.”
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The authors disclosed no relevant financial relationships.
A version of this article first appeared on Medscape.com.