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Soy Protein & Estrogen Risk

I can’t even begin to tell you how many emails I get about soy protein and soy products and its effects on testosterone, muscle growth and even fertility. It doesn’t help either that some bodybuilding sites are completing blasting soy protein while some are writing about the joy of soy. For vegans and some non lacto vegetarian, the use of whey and casein proteins is out of the question, which often means looking to other sources of protein such as soy. Furthermore, being vegan isn’t easy, even compared to vegetarians when it comes to nutrition to promote muscle adaptations. Being a bodybuilder or having big, strong muscles while being vegan is completely possible though. Check out sites like www.veganbodybuilding.com for some examples.

Soy Protein for Muscle

Now back to soy protein. Soy protein and soy products are packed full of nutrients including isoflavones and phytoestrogens, which have been shown in many studies as being beneficial to cardiovascular health. Soy protein is also a complete source of protein meaning it provides all the essential amino acids that our bodies require. However, there has also been some controversy with isoflavones and phytoestrogens and their ability to increase oestrogen levels in men as well as decreasing fertility. A recent review6 showed that soy products and isoflavone supplements did not decrease bioavailable testosterone concentrations in men. It is known that men taking oestrogen supplements for medical reasons, have shifts in their ratios of testosterone to oestrogen levels which can exert feminising effects on the male as well as lowered sex drive and fluctuating mood levels. There has even been a recent case7 where a man was reported to have gynecomastia (man-boobs) which was related to his soy intake. However that man was drinking excessive amounts (2.5L) of soy milk a day. Still other evidence suggests that soybean isoflavone and soy products do not have feminising effects on men8 or dramatically change sex hormone concentrations9 (testosterone or oestrogen) in men or women. Negative side effects of soy and soy product intake can only be attributed to chronically high consumption of soy products at this stage.

Recommended Daily Intake of Soy Supplements

The original dietary recommendations by the American FDA stated that consuming whole soy products containing soy protein levels of 25g may be able to reduce the risk of heart disease. This amount is most likely not capable of increasing body oestrogen levels to detrimental effects or dramatically effect sperm quality or fertility.

Soy vs Whey Protein

In conclusion, soy protein supplementation has been shown to lead to similar muscle protein synthesis as whey and even better muscle protein synthesis capacity than casein.13 However also consider using and cycling other plant source based proteins such as rice protein which can also be quite beneficial. By doing so, you’ll be able to derive your much needed protein from a variety of sources.

Soy & Whey Protein

For those non vegans, a study was even able to show that a soy/whey mixture was capable of producing similar gains in lean mass with higher increases in testosterone and greater concurrent decreases in oestrogen than whey alone.14 While there still needs to be more comprehensive research done on soy and soy products in human health, consuming a varied and moderated diet is still your best bet to achieving your gains and goals.

6 Hamilton-Reeves JM, Vazquez G, Duval SJ, Phipps WR, Kurzer MS, Messina MJ. ‘Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis.’ Fertil Steril. 2010 Aug;94(3):997-1007. Epub 2009 Jun 12.
7 Martinez J, Lewi JE. ‘An unusual case of gynecomastia associated with soy product consumption.’ Endocr Pract. 2008 May-Jun;14(4):415-8.
8 Messina M. ‘Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence.’ Fertil Steril. 2010 May 1;93(7):2095-104. Epub 2010 Apr 8.
9 Kurzer MS. ‘Hormonal effects of soy in premenopausal women and men.’ J Nutr. 2002 Mar;132(3):570S-573S.
10 Nosaka K, Newton M and Sacco P. ‘Delayed-onset muscle soreness does not reflect the magnitude of eccentric exercise-induced muscle damage.’ Scandinavian Journal of Medicine & Science in Sports. December 2002:12(6): 337-346.
11 Chavarro JE, Toth TL, Sadio SM, Hauser R. ‘Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic.’ Hum Reprod. 2008 Nov;23(11):2584-90. Epub 2008 Jul 23.
12 Mitchell JH, Cawood E, Kinniburgh D, Provan A, Collins AR, Irvine DS (June 2001). "Effect of a phytoestrogen food supplement on reproductive health in normal males". Clinical Science 100 (6): 613–8.
13 Tang JE et al. ‘Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men.’ Journal of Applied Physiology September 2009: 107(3): 987-992.
14 Kalman D, Feldman S, Martinez M, Krieger DR, Tallon MJ. ‘Effect of protein source and resistance training on body composition and sex hormones.’ J Int Soc Sports Nutr. 2007 Jul 23;4:4.
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