"Low-fat diets appear to decrease testosterone levels in men, but further randomized controlled trials are needed to confirm this effect," the authors of a meta-analysis of six small intervention studies conclude.
A total of 206 healthy men with normal testosterone received a high-fat diet followed by a low-fat diet (or vice versa), and their mean total testosterone levels were 10% to 15% lower (but still in the normal range) during the low-fat diet.
The study by registered nutritionist Joseph Whittaker, MSc, University of Worcester, and statistician Kexin Wu, MSc, University of Warwick, Coventry, United Kingdom, is published online in the Journal of Steroid Biochemistry and Molecular Biology.
"I think our results are consistent and fairly strong, but they are not strong enough to give blanket recommendations," Whittaker told Medscape Medical News.
However, "if somebody has low testosterone, particularly borderline, they could try increasing their fat intake, maybe on a Mediterranean diet," he said, and see if that works to increase their testosterone by 60 ng/dL, the weighted mean difference in total testosterone levels between the low-fat vs high-fat diet interventions in this meta-analysis.
"A Mediterranean diet is a good way to increase 'healthy fats,' mono- and polyunsaturated fatty acids (MUFAs and PUFAs, respectively), which will likely decrease cardiovascular disease risk, and boost testosterone at the same time," Whittaker noted.
Olive oil has been shown to boost testosterone more than butter, and it also reduces CVD, he continued. Nuts are high in "healthy fats" and consistently decrease CVD and mortality and may boost testosterone. Other sources of "good fat" in a healthy diet include avocado, and red meat and poultry in moderation.
"It is controversial, but our results also indicate that foods with saturated fatty acids may boost testosterone," he added, noting however that such foods are also associated with an increase in cholesterol.
Is Waning Testosterone Explained by Leaner Diet?
Men need healthy testosterone levels for good physical performance, mental health, and sexual health, and low levels are associated with a higher risk of heart disease, diabetes, and Alzheimer's disease, according to a statement about this research issued by the University of Worcester.
Although testosterone levels do decline with advancing age, there has also been an additional age-independent and persistent decline in testosterone levels that began roughly after nutrition guidelines began recommending a lower-fat diet in 1965.
Fat consumption dropped from 45% of the diet in 1965 to 35% of the diet in 1991, and stayed around that lower level through to 2011 (Nutrition. 2015;31:727-732).
However, it is not clear if this decrease in dietary fat intake might explain part of the concurrent decline in men's testosterone levels.
Whittaker and Wu conducted a systematic literature review and identified six crossover intervention studies that compared testosterone levels during low-fat vs high-fat diets — Dorgan 1996, Wang 2005, Hamalainen 1984, Hill 1980 (North American and South African), Reed 1987 and Hill 1979 — and then they combined these studies in a meta-analysis.
Five studies each enrolled 6 to 43 healthy men from North America, the UK, and Scandinavia, and the sixth study (Hill 1980) enrolled 34 healthy men from North America and 39 farm laborers from South Africa.
Overall, on average, the men were 34-54 years old and slightly overweight (a mean body mass index of roughly 27 kg/m2 ) with normal testosterone (ie, >300 ng/dL, based on the 2018 American Urological Association Guidelines criteria).
Most men received a high-fat diet (40% of calories from fat) first, followed by a low-fat diet (on average 20% of calories from fat; range, 7% to 25%), but the subgroup of men from South Africa received the low-fat diet first.
To put this into context, UK guidelines recommend a fat intake of less than 35% of daily calories, and US guidelines recommend a fat intake of 20% to 35% of daily calories.
The low-fat and high-fat interventions ranged from 2 to 10 weeks.
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 (Hill 2018 South African) 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 write.
The decrease in total testosterone in the low-fat vs high-fat diet was largest (26%) in the two studies of men who consumed a vegetarian diet (Hill 1979 and Hill 1980 North American). These diets may have been low in zinc, since a marginal zinc deficiency has been shown to decrease total testosterone, Whittaker and colleagues speculate.
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," Whittaker said.
However, proponents of various diets are often in stark disagreement about the merits of a low-fat vs 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 ("good") 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," 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 have disclosed no relevant financial relationships.
J Steroid Biochem Mol Biol. Published online March 16, 2021. Abstract
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Cite this: Eating More Fat May Boost Borderline Low Testosterone - Medscape - Apr 16, 2021.