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October 11, 2013
FARMINGTON, Conn.Supplementing with soy and whey protein has been shown to have an effect on testosterone, sex hormone binding globulin (SHBG) and cortisol responses in men, according to a study published in the Journal of the American College of Nutrition.
"Our main findings demonstrate that 14 days of supplementation with soy protein does appear to partially blunt serum testosterone," the researchers said. "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."
The study monitored 10 resistance-trained men in their early 20s. For 14 days subjects completed three experimental treatment conditions supplementing with whey protein isolate (WPI), soy protein isolate (SPI) and maltodextrin placebo. Each participant took 20 g of the assigned supplement at the same time each morning followed by an acute heavy resistance exercise test consisting of six sets of 10 repetitions in the squat exercise at 80% of the subject's one repetition maximum.
The investigation observed lower testosterone response following the soy protein supplementation in addition to a positive blunted cortisol response with the use of whey protein at some recovery time points. Although sex hormone binding globulin (SHBG) was proposed as a possible mechanism for understanding changes in androgen content, SHB did not differ between experimental treatments. here were no significant differences between groups in changes in estradiol concentration.
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