Soy Protein Does Not Lower Testosterone
Many strength athletes avoid soy-based protein supplements because they believe that soy lowers testosterone levels, thus potentially limiting muscle mass gains resulting from training. The physiological rationale for this belief is that soy is a rich source of phyoestrogens that are capable of binding to estrogen receptors in the body and thus modulate sex hormone levels.
A group of researchers representing Miami Research Associates recently compared the effects of supplementation with four different protein sources--soy concentrate, soy isolate, a soy/whey blend, and whey protein--on hormone levels, and body composition in 20 men (with an average age of 30 years) enegaging in a 12-week resistance training program. Subjects were randomly assigned to receive only one of the four protein supplements and were blinded to the specific protein type they received. All subjects lifted weights three times per weeks and consumed 50 grams per day of the protein supplement that had been assigned to them.
All four groups exhibited similar increases in lean body mass after 12 weeks. There were no differences in testosterone levels among the four treatments. The researchers concluded, "This investigation shows that 12 week supplementation with soy protein does not decrease serum testosterone or inhibit lean body mass changes in subjects engaged in a resistance exercise program." |
