You are what you eat. Taken literally, people are constructed and renovated by the molecules they ingest and breathe. What people eat also has a surprisingly strong impact on their hormone levels. Turns out, high-protein diets might not be optimal for the gym-inclined.
A study from the Columbia University College of Physicians and the Surgeons and The Rockefeller University Hospital in New York found a causal relationship between protein-carb ratio in diet and testosterone levels. They found that after seven normal men had significantly higher testosterone plasma levels on a 10-day high-carbohydrate diet than they did on a 10-day high-protein diet. Globulin proteins associated with sex hormone binding also increased during high-carb diets. Notably, both diets were controlled for total calorie intake and dietary fat consumption. Researchers conclude:
The diets were equal in total calories and fat. These consistent and reciprocal changes suggest that the ratio of protein to carbohydrate in the human diet is an important regulatory factor for steroid hormone plasma levels and for liver-derived hormone binding proteins.
In a journal aptly titled Steroids, Booth and colleagues published a classic piece on the effects of fasting. They studied 12 male college wrestlers, and found that wrestlers who fasted before the day of their matches had decreasing testosterone (measured salivary testosterone). In contrast, wrestlers who ate normally experienced increasing testosterone during their matches. Researchers note that testosterone levels consistently matched dietary patterns.
Furthermore researchers in Finland found that low-fat high-fiber diets lower testosterone levels in the blood. They studied 30 middle-aged men during a dietary intervention program who were placed on an experimental diet containing high fiber and less fat with high unsaturated-saturated ratio. The resulting decrease in testosterone was significant:
There was a significant decrease in serum total testosterone concentrations (22.7 ± 1.2 vs 19.3 ± 1.1 nmol/1 SEM, P < 0.001). Furthermore, serum free, unbound testosterone fell from 0.23 ± 0.01 to 0.20 ± 0.01 nmol/1 SEM (P < 0.01). The hormonal changes were reversible. This observation suggests that testosterone activity in plasma can at least partly be modified by changing the composition of the diet.
In sum, it seems to maximize testosterone, we should eat carbs and fat and avoid skipping meals. Notably, the effects of perpetually high testosterone aren’t established and may actually be detrimental, despite how effective testosterone therapy is for losing weight and gaining muscle. I’d take these studies with a grain of salt and keep my gym membership.