Effects of soy, whey protein supplementation post-exercise

With protein supplement use by athletes on the rise, a group of researchers recently expanded upon the limited prior research examining the effects of soy and whey protein supplementation on testosterone, sex hormone binding globulin (SHBG), and cortisol responses to an acute bout of resistance exercise.

"This study starts to unravel and provide some insights into one of the real urban myths about soy protein and resistance exercise in men," said Dr. William J. Kraemer, the lead researcher of the study. Using a sample of 10 resistance-trained men in their early 20s, protein supplementation consisted of 3 treatment groups: whey protein isolate, soy protein isolate, or a maltrodextrin placebo control. No other supplements were allowed. Vegetarians, vegans, or subjects who consumed high-protein diets were excluded from the study. For 14 days, participants would ingest 20g of their assigned supplement at the same time each morning. The participants would then perform 6 sets of heavy resistance squats at 10 reps each using 80 percent of their maximum lifting weight.

"Our main findings demonstrate that 14 days of supplementation with soy protein does appear to partially blunt serum testosterone. In addition, whey influences the response of cortisol following an acute bout of resistance exercise by blunting its increase during recovery. Protein supplementation alters the physiological responses to a commonly used exercise modality with some differences due to the type of protein utilized," wrote the researchers.