Soy Protein May Not Be So Bad
It is often rumored that soy protein consumption causes increased testosterone in men.
Previous work has suggested that soy protein is preferentially directed towards the splanchnic region (soft tissue organs) and milk proteins (whey and casein) to the peripheral regions such as muscle tissues. When compared to soy proteins, milk proteins provide greater amounts of the branched chain amino acids (BCAAs) leucine, isoleucine and valine, as well as methionine and lysine. Recent work has identified the importance of the BCAA leucine in the activation of myogenic translation initiation factors, which are considered important for muscle hypertrophy.
Soy foods, including soy protein supplements, contain phytoestrogens (isoflavones), which are a group of natural estrogen receptor modulators. Soy isoflavones have comparable molecular weights and are structurally similar to 17-beta estradiol, which may enable them to exert estrogenic and antiestrogenic activities through their associated receptor-binding site. In-vitro studies have supported this relationship by demonstrating the ability of soy to inhibit a variety of androgenic and estrogenic hormones including testosterone, sex hormone binding globulin (SHBG), esterone, and testosterone/estradiol ratio.
The referenced study assessed the effect of 12 weeks of resistance training and dietary supplementation with soy, whey or a combination, on body composition and plasma sex hormone concentrations. Twenty young, healthy men (age 30.7 plus/minus 6.5 years; weight 82.0 plus/minus 12.3 kg (180 plus/minus 27 lbs) ) completed the 12 week study.
Subjects supplemented their diets with one of four protein powders: soy protein isolate (SI), soy concentrate (SC), whey blend (50% when concentrate, 50% whey isolate) (WB), or a 50:50 mixture of soy isolate and whey blend (SW).
Weight training was performed 3 days per week for 12 weeks with individual instruction once per week by a qualified personal trainer.
The results of the study showed no significant decrease in serum androgenic hormones following supplementation with any of the proteins. The authors concluded that both soy and whey supplementation in resistance training men results in lean body mass increases without negatively affecting serum androgen levels.
It appears that soy protein supplementation does not cause an increase in estrogen in men. Personally, I use a more high quality protein source such as whey or casein. This supplies more BCAAs and provides a more conducive diet for muscle growth. For more information on protein requirements check out a previous post here.
Reference:
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Related posts:
- Weekly Nutrition Tip #14
- Branched-Chain Amino Acids
- Weekly Nutrition Tip #18
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