The effects of soy and whey protein supplementation on acute hormonal reponses to resistance exercise in men

For many resistance-trained men concerns exist regarding the production of estrogen with the consumption of soy protein when training for muscle strength and size. Thus, the purpose of this investigation was to examine the effects of soy and whey protein supplementation on sex hormones following an acute bout of heavy resistance exercise in resistance-trained men.

10 resistance-trained men in their early 20s were divided into 3 supplementation treatment groups: (1) whey protein isolate, (2) soy protein isolate, or (3) 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.