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Soy Protein, Demystified

by Dr. John DeCosmo

Soy consumption has become a controversial topic. There have been some claims during the last few years suggesting that soy protein is problematic and cites issues ranging from unwanted decreases in testosterone to increases in estrogen levels and growing man breasts to causing cancer.  A lot of this soy bashing originated in the bodybuilding industry, which is centered on using whey protein to promote muscle growth.  Others are purposefully taking things out of perspective by citing flawed studies.  Some have good points to make, both pro and con about protein.  However, now that we in the medical community have had the opportunity to analyze these claims over the years it’s apparent that soy protein is a good choice for both weight loss and muscle growth after all.

The Agency for Healthcare Research and Quality (AHRQ) released a nearly 400-page report on the effects of soy and soy isoflavones (antioxidants found in soy), concluding that, "For all outcomes, including adverse events, there is no conclusive evidence of a dose-response effect for either soy protein or isoflavone."  Yet also keep in mind that soy products come in a wide variety ranging from whole soy to fermented soy and soy protein isolates, among others.  ITG Diet uses protein from several healthy sources including soy protein isolates which are clearly in the group referenced positively by the AHRQ.

After years of controversy the bodybuilding industry is now accepting soy protein as a key to muscle growth.  David Robson, a bodybuilder and accredited personal trainer who uses the latest cutting edge research to enhance his own progress says, “As is so often the case, when a particular scientific issue is debated, there is another side to the story.  In recent years, scientists have been looking closely at the effects soy consumption really has on testosterone, and muscle gain.  Recent studies have suggested soy to be as effective, if not more so, than whey in terms of its ability to promote gains in lean muscle mass.”(1)

What’s so good about soy?

Soybeans were introduced into the United States in the 1880s.  Before then, soy was a staple of the Asian diet, and today it’s used in countless products around the globe.  In America it’s difficult to live a day without consuming a soy product because of its prevalence. 

Soy protein comes from the leguminous soybean plant.  It’s been in the human food chain for over 5,000 years.   It’s the only plant-based protein considered to be a high-quality protein because it contains all of the essential amino acids in the ratios needed to support growth and development.(2,3)

Soy protein is also of the highest quality.  Under guidelines adopted by the Food and Drug Administration and the World Health Organization for evaluating protein quality for children and adults, soy protein isolate receives a rating of 1, which is the highest possible score.  This means that the quality of soy protein is equal to that of meat and milk proteins.

Soy is composed of 38% protein, 18% oil (85% of this unsaturated), and 14% moisture, and because it contains all nine essential amino-acids, it’s in the perfect ratio for health and well-being.  Soy's other nutritional functions include providing a respectable amount of potassium, zinc, iron, vitamin-E and phosphorous as well as the full B-complex.(3,6,7)

Soy versus Whey

ITG uses both soy and whey proteins in its products so it was interesting that the Solae Company conducted an in-depth study on whey and soy protein and concluded that both protein sources resulted in the desired effect of increasing lean body mass.  There was no difference between these two protein sources regarding changes in testosterone levels.  Solae also studied the lean muscle mass gains and found they are consistent with prior research looking at how soy and whey impact lean muscle mass in conjunction with an exercise regimen.(4)

Additionally, supplementing with soy protein may provide additional health benefits when combined with a healthy diet including reduced risk of coronary heart disease.  Further studies show that soy protein consumption may even reduce the risk of certain kinds of cancer.  Solae’s study is consistent with other studies which demonstrate the unique benefits that soy protein has when used in conjunction with exercising to improving antioxidant status. These studies also indicate that supplemental soy protein can help combat free radical formation during exercise, which may help speed muscle recovery after exercise.(4)

Greg Paul, Ph.D., director of health and nutrition for the Solae Company says, “The results of this study show that soy protein is just as effective as whey protein in building lean muscle mass as part of a dedicated exercise and nutrition regimen, while contradicting the myth that soy protein may negatively impact testosterone levels in men.”

Some consider soy to be the perfect food

Few products contain as many good attributes as soy does. "Just imagine you could grow the perfect food. This food not only would provide affordable nutrition, but also would be delicious and easy to prepare in a variety of ways. It would be a healthful food, with no saturated fat. In fact, you would be growing a virtual fountain of youth on your back forty," wrote the author Dean Houghton, in The Furrow, a magazine published in 12 languages by John Deere. “This ideal food would help prevent, and perhaps reverse, some of the world's most dreaded diseases. You could grow this miracle crop in a variety of soils and climates. Its cultivation would build up, not deplete, the land... this miracle food already exists... It's called soy."(5)

How about estrogen and other health claims?

One of the claims made by soy detractors is that soy proteins cause increases in estrogen in males. First, let’s remember that all men have estrogen in their bodies as a part of their natural physiology; so estrogen is not a foreign hormone whether naturally derived or soy derived. Second, a study conducted by the Miami Research Associates refutes the finding of the Goodin study, finding soy protein had no significant impact on testosterone levels in healthy males.(8,9) There simply isn’t evidence that a healthy diet including soy products will cause a man to grow breasts.   

On the flipside, research regarding soy protein and cardiovascular health has become so robust that it was awarded a health claim, allowing food companies to state that “25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.”  Soy’s cancer-preventing properties stem from isoflavones and there are even more studies claiming that soy has been reported to reduce inflammation by reducing interleukin 6 and may help in leukemia.(10)

The isoflavones controversy

Perhaps the most controversial area regarding soy are its concentrated isoflavones, which are the antioxidants famous for mimicking estrogen in the body.  This effect has been seen as a benefit, with research showing that 75 milligrams a day of soy isoflavones can increase bone mineral density and decrease the frequency and severity of hot flashes, respectively.  However, isoflavones in soy have also been proposed to play a role in increasing risk of breast cancer.  The research in this area is complicated and constantly evolving, with negative effects seen in animal studies, but no effects found in human studies.(11)

It’s also important to note that soy protein isolate isn’t necessarily a concentrated source of isoflavones.  According to the USDA Isoflavone Database, one ounce (about one scoop) of soy protein isolate contains 28mg soy isoflavones and three ounces of cooked tofu contain 23mg soy isoflavones.  On a per-serving basis, both foods contain about the same dose of isoflavones, but soy protein isolate contains significantly more protein: 23g vs. 8g.(11)

All things considered, eating moderate amounts of soy protein isolate does not provide a health risk.  I see the main benefit of soy protein isolate as a nutritional tool to help you meet your daily protein needs.  If you abstain from eating dairy protein (whey) right after a workout or if you need to increase the protein at a given meal, use soy protein as you would use any protein supplement.(11)

Soy has a huge following.  It’s a daily part of most of our diets already.  The question of whether soy is good or bad for you has been a tricky one for both traditional medical and alternative medical communities.  This applies to the layperson as well as the medical professional.  The concern of soy products in the diet is a valid one, just as we should all be concerned about everything we consume.  Yet history and serious studies have shown time and again that soy protein is a great source of protein while its detractors have failed to make a convincing case against it. 

The evidence supporting the benefits of soy protein is a long and proven list from accredited sources while the claims against soy are not supported to this degree.  So while keeping in mind that nearly all things we consume have both good attributes and bad attributes, let’s remember that soy has a keen track record that far out shadows the claims against it.



1          Soy vs. Whey, By David Robson, http://www.bodybuilding.com/fun/drobson71.htm  

2           Segounis, S.(2004). The Scoop on Protein Powders. True Star Health. [Online] http://www.truestarhealth.com/members/cm_archives12ML3P1A8.html .

3           The Solae Company.(2004). Soy Essentials. [Online]

4           Samantha Rubin, Douglas Kalman, Michele Martinez, Diane R. Krieger, Nutrition Miami Research Associates.(2005). A Randomized Double-Blind Clinical Pilot Trial Evaluating the Effect of Protein Source when Combined with Resistance Training on Body Composition and Sex Hormones in Adult Males. Experimental Biology 2005, April 5.

5           Houghton, Dean, "Healthful Harvest", The Furrow, January 2000, pp. 10-13.

6           "National Soybean Research Laboratory". Nsrl.uiuc.edu. Retrieved 2011-09-29.

7           Jump up^ Soy: Health Claims for Soy Protein, Questions About Other Components

8        Dillingham BL, McVeigh BL, Lampe JW, Duncan AM (March 2005). "Soy Protein Isolates of Varying

Isoflavone Content Exert Minor Effects on Serum Reproductive Hormones in Healthy Young Men". Journal of Nutrition 135 (3): 584–591. PMID 15735098.

9        Kalman D et al. (2007-07-23). "Effect of Protein Source and Resistance Training on Body Composition and Sex Hormones". J Int Soc Sports Nutrition 4 (1): 4. doi:10.1186/1550-2783-4-4. PMC 1997115. PMID 17908338.

10      Scalable purification and characterization of the anticancer lunasin peptide from soybean". PLoS ONE 7 (4): e35409. 2012. doi:10.1371/journal.pone.0035409.PMC 3326064. PMID 22514740.

11      Dr. Mike Roussell, Ask the Diet Doctor: The Last Word on Soy Protein Isolate, Diet Tips, Jun 03, 2014


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