“The moral is that healthy men who are of normal weight with no significant comorbidities are unlikely to benefit from restrictive diets,” said Dr. Richard J. Fantus, one of the study’s authors and a urologist at NorthShore University HealthSystem in Evanston, Ill.
Diet studies are complicated, because changing one component of the diet, such as fat intake, alters so many other things, such as the amount of carbohydrates, protein and micronutrients consumed. It’s unclear which component of the diet may have prompted the hormonal changes, Dr. Bhasin said. Furthermore, testosterone levels may also be shaped by how much a person sleeps, or whether they are jet-lagged, or if they are eating most of their calories at night or in small meals throughout the day.
Dr. Faysal Yafi, chief of the division of Men’s Health and Reconstructive Urology at the University of California, Irvine, says his patients who opt to follow specific diets tend to start exercising more and drinking less alcohol, all of which can raise testosterone levels. He suspects any links between diet and testosterone may be the result of an overall healthier lifestyle.
Some men worry that eating lots of soy foods may cause their testosterone levels to fall, because soy is rich in isoflavones, which mimic the structure of estrogen. But the evidence doesn’t support their concerns, even if men eat foods like miso, tofu or soy milk at every meal. (Doctors did report one anecdotal case in which a 19-year-old man with Type 1 diabetes who followed a vegan diet containing 360 milligrams of soy isoflavones daily — nine times higher than a typical Japanese diet, and 100 times higher than the typical American diet — developed low testosterone levels along with low libido and fatigue. His symptoms improved when he stopped eating the soy-heavy, vegan diet.)
Long-term alcohol abuse lowers testosterone by damaging cells in both the testes, which make testosterone, and the liver, which alters testosterone metabolism. But binge drinking every now and then does not appear to have much of an impact — it lowers testosterone for only about 30 minutes, according to one study, after which levels bounce back to baseline.
Obese men who have low levels of testosterone can increase levels by cutting calories and losing weight — the type of diet does not matter, studies suggest. On the opposite extreme, Dr. Bhasin said he is seeing an increasing number of men at his clinic who have body dysmorphic issues and are suffering from low libido and fatigue. Strict calorie restriction, exercising intensely and being chronically stressed can all cause testosterone levels to plummet and are likely to blame, he said.
The bottom line is that for otherwise healthy men who are following a reasonably healthy lifestyle, fiddling with specific foods or the composition of the diet is not likely to make much of a difference on the testosterone score card. As Dr. Fantus of NorthShore University put it: “I don’t think there is a way to game the system to get really large increases by changing the diet.”