FAT: How Much Is Enough?
Several clinical studies have connected low-fat diet regimens with decreased serum free-testosterone levels. One such study measured the effects of both high-fat and low-fat diets on free-testosterone levels. Six healthy men were placed on isocaloric, weight-maintaining diets providing 100 grams of fat per day for 2 weeks. (This would be 36% of your total calories on a 2,500-calorie diet.) Free-testosterone levels were measured; then their diets were changed to include less than 20 grams of fat per day (7% of total calories on a 2,500-calorie diet), while still supplying a maintenance calorie level. They consumed this new lower fat diet for two weeks. Serum-free-testosterone levels were measured again.
When the two measurements were compared, they observed the biologically active free-testosterone percentage had dropped from 2.8 on the high-fat diet to 2.2 on the low-fat diet.(5)
The higher fat diet produced a 27% increase in circulating levels of metabolically active free testosterone over the lower fat diet! This is obviously a substantial increase. But at 36% vs. 7% fat intake, this study focused on some rather extreme levels of fat consumption. Maybe you’re thinking to yourself, “Well, I usually consume about 10% of my calories as fat, so that probably doesn’t apply to me.” Think again!
Other studies have indicated that even a more moderate fat-restricted diet can negatively affect free-testosterone levels. For example, 2 separate studies have shown a decrease in fat intake from 40% to 20% and from 37% to 25% leads to decreases in metabolically active free testosterone levels of 19% (from 1.06% to 0.86%)4 and 13% (from 0.23 to 0.20 nmol/l)(3), respectively. Investigators from one of the aforementioned studies felt confident enough about their results to state that, “The reduction of total plasma testosterone observed in the present study is in agreement with previous findings. ...showing that a low-fat diet reduces the biologically active free testosterone in serum.”(3)
Given the evidence, it appears these investigators believe the verdict is in, and low fat is out. However, the question remains—is more better, or is there a point of diminishing returns?
How Much Is Too Much?
It appears 40% of calories from fat just may be the diminishing point, at least according to a study conducted at the Novum Research Center in Huddinge, Sweden. This study enlisted players from two elite male hockey teams as subjects. One team was put on a less-than-30%-fat diet, while the other was allowed to eat their normal diet, consisting of approximately 40% of calories from fat.
At the end of the 7-month study period, which spanned their competitive season, the free-testosterone concentrations of the players on the “30% team” were found to be approximately 22% higher, on average, over the “40% team” (22 vs. 18 nmol/l).(6)
These findings were supported by a related study which showed a negative correlation between fat intake and free-testosterone levels among identical male twins. In other words, subjects consuming an average of 41% of their calories from fat had significantly lower free-testosterone levels compared to their identical twins who consumed 36% of their calories from fat.(2)
From this information, we can extrapolate the approximate range of fat intake needed to help promote peak levels of biologically active free testosterone in the bloodstream is somewhere between 20% and 40%.
References Cited
1 T. Akerfeldt, Unpublished Research (Department of Medical Sciences, Nutrition Unit, Uppsala University, 1998).
2 D.T. Bishop, et al., “The Effects of Nutritional Factors on Sex Hormone Levels in Male Twins,” Genet. Epidemiol. 5.1 (1988) : 43-59.
3 E.K. Hamalainen, et al., “Decrease of Serum Total and Free Testosterone During a Low-Fat High-Fibre Diet,” J. Steroid Biochem. 18.3 (1983) : 369-370.
4 D.M. Ingram, et al., “Effect of Low-Fat Diet on Female Sex Hormone Levels,” J. Natl. Cancer Inst. 79.6 (1987) : 1225-1229.
5 M.J. Reed, et al., “Dietary Lipids: An Additional Regulator of Plasma Levels of Sex Hormone Binding Globulin,” J. Clin. Endocrinol. Metab. 64.5 (1987) : 1083-1085.
6 R. Tegelman, et al., “Effects of a Diet Regimen on Pituitary and Steroid Hormones in Male Ice Hockey Players,” Int. J. Sports Med. 13.5 (1992) : 424-430.