The Skinny on Dietary Fat and Testosterone
By Layne Norton, Ph.D. candidate
“I think that testosterone is a rare poison.”
While some may consider testosterone a poison, to those in the bodybuilding industry testosterone is King. Few molecules are held in such high regard within the bodybuilding community as testosterone. It is a word that evokes strong visions of anabolism, muscle, and quite frankly, getting straight-up JACKED. It is no surprise that people have spent many years trying to optimize testosterone levels. For some, that means the use of exogenous hormones. For the majority of us however, maximizing testosterone though diet, training and supplementation is our main focus.
For years, many top trainers and gurus have told us that in order to maximize testosterone, we need enough fat in our diet. In recent years however, there are those who have taken this idea to the extreme and claimed that very high-fat diets will help increase testosterone above normal levels. Others have also claimed that high-fat diets will also help prevent testosterone decreases while dieting. Is this truly the case? Is a high-fat diet the way to testosterone Heaven? Keep reading, because it’s time to break it down.
The reasoning behind the theory by which dietary fat increases testosterone is quite simple. Eating high-fat meals will increase cholesterol and since testosterone is synthesized from cholesterol, a high-fat meal will increase testosterone production, due to increased VLDL cholesterol.1 Metabolism, however, is not this simple. There are several regulatory steps involved in turning cholesterol into testosterone and unfortunately for us, it is not as easy as merely increasing fat/cholesterol input to get more testosterone output. If this were the case, we would expect to see testosterone increase in response to a high-fat meal.
The reality is that research has actually demonstrated the opposite! That’s right, several studies have shown that high-fat meals actually decrease post-meal testosterone concentrations!2,3 Unfortunately, researchers have provided few possible mechanisms to explain this surprising outcome. Some have suggested that chylomicrons formed during absorption of fats may impair luteinizing hormone release and impair testosterone production, as was previously demonstrated in vitro.4 This theory does not appear to hold up in vivo, however.3 Another theory suggests specific fatty acids somehow inhibit testosterone production in the testis, but little research has been done in this area.4
Demonstrating that high-fat meals may decrease testosterone output acutely is interesting, but the most important overall factor is long-term effects of various fat intakes on testosterone levels. There is strong evidence to suggest dietary fat intakes below 15-20 percent of total calories reduce testosterone levels.5,6 It has also been demonstrated that high-fat diets (>40 percent calories from fat) will increase testosterone, relative to low-fat diets.5,7 It is important to note, however, that while prolonged feeding of a high-fat diet initially increases testosterone, over time testosterone levels may eventually decline to below the initial testosterone levels!6,8
What is less clear is whether high-fat intakes can increase testosterone relative to moderate levels of dietary fat. Perhaps the best study examining this subject was performed by Volek et al.9 The researchers compared six weeks of feeding subjects an isocaloric high-carb low-fat diet (about 56 grams/day, approximately 26 percent of calories) vs. those fed a high-fat low-carb diet (about 157 grams/day, approximately 61 percent of calories) and measured differences in various hormones (including testosterone), fat mass, and body composition. The researchers found that there were no differences between the groups in total testosterone or free testosterone after six weeks of feeding the respective diets.
The low-carb, high-fat group did, however, retain more lean body mass and lose more body fat during the six-week diet, but this was likely due to the doubled protein content of the high-fat, low-carb diet vs. the low-fat, high-carb diet (176 grams/day vs. 88 grams/day). The differences in lean body mass could not be explained by any effects of dietary fat on testosterone, since there were no differences in testosterone levels between groups. It is also important to note that this was a weight-loss trial and so these results also demonstrate that super high-fat diets are not better for maintaining testosterone levels during caloric restriction vs. a moderate-fat diet.
Within this discussion, it is important to keep a few things in mind. Many of these studies refer to fat intake in percentages of total calorie intake. The problem with this is that 30 percent fat from calories, if you are consuming 3,000 total calories, is much different from 30 percent of calories from fat at 2,000 calories (i.e., 100 grams of fat vs. about 67 grams of fat). Therefore, referring to a fat intake as ‘high’ or ‘low’ based purely on percentages is misguided, as it is quite likely that it is a specific amount of fat intake that is required to get the aforementioned benefits from dietary fat, not a percentage of calories. Based upon the currently available research, it is impossible to currently determine how exactly these benefits are reached. Furthermore, while testosterone is a very important muscle-building hormone, it is crucial to acknowledge that it is not the only factor involved in building muscle. If your dietary fat intake is too great a proportion of your caloric intake, you may miss out on some of the benefits of consuming enough protein and carbohydrates. Therefore, it is important to maintain a healthy balance of protein, carbohydrates, and fats in order to try to maximize the benefits of each.
At this point, many questions still remain unanswered regarding dietary fat intake and testosterone production. What can be concluded with current information is that very low-fat diets (<15-20 percent kcals from fat) can reduce testosterone, and consuming a moderate-fat diet will normalize testosterone. Furthermore, consuming a very high-fat diet (>40 percent calories from fat) compared to a moderate fat (25-30 percent calories from fat) diet will not further increase testosterone.