Fat Test

Does the nutrient content of a meal affect levels of testosterone in the body? Two new studies examined that issue. In the first study 15 men ate meals containing the same number of total calories but varying in types of proteins and quantities of fat.1 The subjects ate four test meals in random order:

1) A lean-meat meal containing 20 percent fat

2) A tofu (soy) meal containing 20 percent fat

3) A meat meal with added fat from safflower oil containing a total of 54 percent fat

4) A meat meal with added fat from animal fat sources containing a total of 54 percent fat

The authors took blood samples from the men at baseline and at two, three and six hours after the meals. They found a significant decrease in testosterone levels after the tofu and lean-meat meals within two hours. Testosterone levels also dropped after the meat meal with added safflower oil but not after the meal with added animal fat. The researchers aren't sure what caused the food-based effect on testosterone levels, but they suggest that it may be either increased clearance of testosterone in the liver or some effect of fatty acids on testosterone secretion.

The tofu meal produced a significant increase in the level of sex-hormone-binding globulin (SHBG), a liver-produced protein that effectively binds testosterone in the blood, making it inactive. While isoflavones, such as genistein and diadzein, found in soy foods such as tofu, are known to interfere with testosterone release, the speed of the increase in SHBG that occurred after the tofu meal was likely related more to the meal's lowfat content.

Other studies show that eating a high-fat meal may lower testosterone levels by as much as 30 percent within four hours. That effect was thought to be due to chylomicrons, which are products of fat digestion that may reduce the secretion of luteinizing hormone (LH) from the brain's pituitary gland. LH controls testosterone synthesis in the testes, and limiting its release would lower testosterone synthesis in the body.

A recent study, however, showed that chylomicrons don't lower testosterone levels.2 The study also noted that switching from a diet containing 20 percent fat to one with 40 percent fat increases testosterone levels. The effect is limited, since in the new study increasing fat intake from 37 percent to 67 percent didn't increase testosterone levels. It would probably also put you at risk for cardiovascular disease and obesity.

1 Habito, R.C., et al. (2001). Postprandial changes in sex hormones after meals of different composition. Metabolism. 50:505-511.
2 Volek, J., et al. (2001). Effects of a high-fat diet on postabsorptive and postprandial testosterone responses to a fat-rich meal. Metabolism. 50:1351-1355.