The Secret of Soy

It's not just for "granola" dudes anymore.
Ismael Roldan


Despite its quality amino acid ratio, there has always been much controversy over soy’s effectiveness in stimulating protein synthesis and, therefore, promoting muscle growth. However, numerous studies support the conclusion that soy is similar to whey when it comes to fueling muscle growth.

A study from Ohio State University (Columbus) found that males supplementing their diet with 33 grams of soy or whey protein, in the form of a protein bar, significantly increased their muscle mass after a nine- week weight-training program. Those not supplementing with either protein did not gain any muscle mass.

In another study, presented at the Experimental Biology conference in San Diego, California, researchers discovered that when male bodybuilders consumed either soy protein concentrate powder, soy protein isolate powder, a soy/whey protein powder blend or a whey protein isolate powder twice daily during 12 weeks of weight training, they all increased muscle mass similarly.

The most recent study showing soy’s impact on muscle growth dealt with the molecular aspects of muscle protein synthesis. Researchers from Indiana University School of Medicine (Evansville) reported in an issue of the Journal of Nutrition that rats fed either soy protein with carbs or whey protein with carbs increased post-exercise protein synthesis significantly more than those fed just carbs. However, whey did lead to better stimulation of critical components involved in protein synthesis.


In addition to the clear benefits of soy on muscle growth, research indicates that soy can help protect muscle from oxidative damage following exercise, leading to enhanced recovery. The OSU study further reported that the men taking soy had better antioxidant protection after exercise. Another inquiry, published in the International Journal of Sports Nutrition and Exercise Metabolism, concluded that men who consumed 40 g of soy protein during a four-week program had better antioxidant protection following weight workouts, as compared to men who consumed whey protein. And, research published in the Journal of Sports Medicine and Physical Fitness revealed that women consuming soy protein for four weeks had less oxidative muscle damage postexercise than those consuming whey, who had no such reduction.

Soy protein powder is especially beneficial for those who are lactose intolerant. Lactose is the carbohydrate in milk and milk products that many people have difficulty digesting. Since both whey and casein are derived from milk, some people also have problems digesting these forms of protein powder. For them, soy is a good option for getting the extra protein needed for max muscle growth. 


Male bodybuilders fear soy for its isoflavones — but they offer many health benefits. Research indicates that these powerful antioxidants may fight certain types of cancer (particularly prostate, colorectal and breast), lower cholesterol levels and reduce the risk of cardiovascular disease (a rare FDA-approved health claim).

However, the chemical structure of soy isoflavones closely resembles that of estrogen. This has caused many a man to worry that the estrogenlike isoflavones will compete with testosterone’s anabolic effects and, worse, even lower their testosterone levels. The good news is that none of this is actually true. The studies mentioned above reported that males taking soy had similar increases in muscle mass to those taking whey. 

Muscle mass gains would not have been possible had their testosterone levels been compromised. Likewise, the Experimental Biology study that provided male bodybuilders either soy, whey or a mix of both protein sources twice a day for 12 weeks reported no changes in the men’s testosterone or estrogen levels. Recently, Cancer Epidemiology Biomarkers & Prevention reported that males taking soy protein powder had reduced levels of testosterone. However, the study was flawed, and contradicted the plentiful research indicating soy has no effect on testosterone in males. 


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