Low-Fat Diets and Testosterone in Men
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Why Testosterone Matters
Testosterone plays a key role in men’s health. It supports muscle growth, bone strength, mood, and reproductive health. Low testosterone levels have been linked to higher risks of chronic diseases, such as heart disease and type 2 diabetes, as well as reduced quality of life. In recent decades, studies have shown that men’s testosterone levels have been falling, even after adjusting for age and body weight. This has raised questions about possible causes, including changes in diet.
The Changing Diet Landscape
Since the 1960s, dietary guidelines in many Western countries have recommended reducing fat intake to improve heart health. As a result, average fat consumption dropped significantly, while carbohydrate intake rose. For example, between 1965 and 1991 in the US, fat intake fell by about 10% of total daily calories. At the same time, testosterone levels began to decline, leading researchers to wonder if these two trends might be connected.
What the Research Looked At
A 2021 systematic review and meta-analysis examined this possible link. Researchers looked for high-quality intervention studies that compared low-fat diets (around 20% of daily calories from fat) with higher-fat diets (around 40% of daily calories from fat) in healthy adult men. They focused on studies lasting at least one week, ensuring that the diets were otherwise balanced and not influenced by other factors like extreme weight loss or supplements. Six eligible studies were found, involving a total of 206 men.
Key Findings
The results showed that low-fat diets led to small-to-moderate decreases in several important hormones:
- Total testosterone dropped by an average amount that was statistically significant
- Free testosterone, the form most available for the body to use, also decreased
- Urinary testosterone and dihydrotestosterone (DHT) levels fell
- There were no significant changes in luteinising hormone (LH) or sex hormone binding globulin (SHBG), suggesting the main effect was on testosterone production, not how it was bound or regulated in the blood
Interestingly, the reduction in testosterone was more pronounced in men of European or North American descent compared to a South African group in one study.
Why Might Low-Fat Diets Lower Testosterone?
The review suggests several possible reasons:
- Lower intake of certain fats: Monounsaturated fats (found in olive oil, nuts, and avocados) and saturated fats (found in dairy, meat, and coconut oil) may support testosterone production. Low-fat diets tend to reduce these fats and increase the ratio of polyunsaturated fats, especially omega-6 fats, which might impair testicular function.
- Micronutrient differences: Vegetarian-style low-fat diets could be lower in zinc, a mineral important for testosterone production.
- Changes in cholesterol availability: Testosterone is made from cholesterol, so very low cholesterol intake could slightly limit production, although the relationship is complex.
- Oxidative stress: High omega-6 intake from certain vegetable oils may increase oxidative stress in the testes, potentially lowering testosterone.
Practical Implications
For men concerned about their testosterone levels, these findings suggest that extremely low-fat diets may not be ideal. This doesn’t mean that very high-fat diets are automatically better for overall health, but it highlights the importance of dietary balance. Including healthy sources of fat—such as olive oil, nuts, seeds, dairy, eggs, and fatty fish—may help maintain hormone health.
It’s also important to remember that testosterone is influenced by many factors, including body weight, exercise, sleep, and overall nutrition. A low-fat diet that is also low in calories and nutrients, combined with stress or poor sleep, could have a bigger impact on hormone levels than fat intake alone.
Limitations of the Research
While the review’s findings are consistent, the number of studies was small, and most lasted only a few weeks. We don’t know if the testosterone drop would be larger, smaller, or stable over many months or years. Also, most participants were middle-aged men, so results might differ for younger or older men.
Bottom Line
This review suggests that low-fat diets can reduce testosterone in men, likely by lowering production in the testes. Men—especially those of European descent—may be more affected. More large, long-term studies are needed to confirm these results and to understand how diet, ethnicity, and lifestyle interact to influence testosterone. In the meantime, aiming for a balanced diet with adequate healthy fats is a sensible approach for both general health and hormone balance.