New research published in The Journal of Steroid Biochemistry and Molecular Biology has found that low fat diets decrease men’s testosterone levels by 10-15%.

Low testosterone levels are linked to a higher risk of heart disease, diabetes, and Alzheimer’s disease; while healthy levels of the hormone are key for men’s athletic performance, mental health, and sexual health.

For these reasons, optimal testosterone levels are critical to men’s health and well-being.

The researchers from the University of Worcester hope that the data will be useful for treatment of low testosterone, as rates of hypogonadism (medically low testosterone) have been on the rise since the 1970s.

Testosterone levels decreased by 10-15% for those on a low-fat diet

The study was a systematic review and meta-analysis, which combined together the results of 6 well-controlled studies with a total of 206 participants. These studies first put men on a high fat diet (40% fat), and then transferred them to a low-fat diet (20% fat), and found their testosterone levels decreased by 10-15% on average.

Vegetarian low-fat diets had a particularly harmful effect, causing decreases in testosterone levels up to 26%.

Similar studies have been conducted previously on humans and mice. The authors linked their results to these studies, highlighting the difference monounsaturated fats and polyunsaturated fats have on testosterone production.

These studies found that high intakes of monounsaturated fats found in olive oil, avocados, and nuts may boost testosterone production. However, omega 6 polyunsaturated fats predominantly found in vegetable oils, may damage the cells’ ability to produce testosterone. This is because highly unsaturated fats such as polyunsaturated fats are more prone to oxidation, which causes cell damage.

However, some types of fats may damage the cell’s ability to produce testosterone

The authors say that further research needs to be done in this important area. The lead researcher of the study Joseph Whittaker said: “Ideally, we would like to see a few more studies to confirm our results. 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”.

Dietary fat is already a controversial topic in nutritional science, with proponents of various diets often in stark disagreement (low fat vs low carbohydrate).

Traditionally, dietary guidelines have focused on limiting fat intake, with the current UK and US guidelines suggesting fat should make up less than 35% of total calories.

However, many studies have shown high fat diets can decrease triglycerides, decrease blood pressure, increase HDL cholesterol (aka ‘good cholesterol’), and now with this paper: increase testosterone levels. With this new research, the debate is bound to become more complex.