Attention: a valuable bodybuilding nutrient has gotten a bad rap — here, we set the record straight on soy protein.

Soy protein powder is the most misunderstood and underrated protein powder on the market today.

Do we have your attention? If you’ve been a victim of the misinformation permeating the bodybuilding community, you’re probably thinking that statement is ludicrous. After all, many male bodybuilders fear anything with soy in it, and more than a few so-called nutrition experts have wrongfully bashed this potent muscle builder.

Perhaps the confusion is due to the fact that  most of the research on soy protein that has made media headlines lately focuses on its health benefits for females, which are due mainly to its estrogen-like effects. Yet, lost in the shuffle is the fact that studies show soy has no negative impact on male testosterone levels and, further, confirms that it has clear muscle- boosting benefits.

Have you been missing out on the bodybuilding benefits of soy? Most likely, the answer is yes, and if so, it’s time you learned the truth.


Soy is a plant protein, and the general rule about plant proteins is that most are incomplete — i.e., they don’t contain all the amino acids the body needs for processes such as muscle growth.

Soy is not ordinary plant protein, however: it does contain all the required amino acids. To be honest, soy is a bit low in the essential amino acid methionine, yet it really doesn’t contain much less methionine than that in quality protein whey. And, when soy is compared to whey on what scientists call the protein digestibility corrected amino acid score, which tests how much of a protein’s critical aminos are properly digested and delivered to the muscles to build muscle mass, they both rate 100%. Black beans, in comparison, score only 85% on the scale.

Soy’s amino acid profile is actually very similar to whey’s. In fact, soy has a higher concentration of arginine and glutamine than whey does. Arginine is critical for stimulating nitric oxide production, which has numerous beneficial properties such as increasing blood flow to muscles to deliver more nutrients, anabolic hormones and oxygen for better recovery and greater muscle protein synthesis. Arginine can
also enhance growth hormone release. Glutamine has a multitude of benefits, including aiding muscle growth, decreasing muscle breakdown, enhancing immune function, decreasing fatigue during workouts, improving GH levels and even aiding fat loss.


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. 



With the overwhelming evidence at your disposal, now is the time to make soy a part of your nutritional regimen. Don’t be one of the misinformed masses when it comes to soy protein. Instead, get an edge on your bodybuilding brethren with what may be the best-kept supplement secret among serious lifters.


Soy protein is similar to whey in rate of digestion and absorption — fast. Like whey, soy boosts protein synthesis and insulin levels, and its amino acid profile enhances whey’s. For maximum benefit, consider taking soy and whey at these times. 

1. First thing in the morning A fast-digesting protein like soy will give your body a source of aminos to burn, therefore sparing your muscles. Soy’s arginine content will also help to raise NO levels. Take 10-20g of soy protein powder mixed with 10-20g of whey protein powder as soon as you wake up.

2. Immediately before workouts Getting in a fast-digesting protein like soy will help to prevent muscle breakdown during training and boost protein synthesis immediately afterward. Since it boosts NO levels, it will maximize blood flow to working muscles. Take about 10g of soy protein powder mixed with 10g of whey protein powder within 30 minutes before workouts.

3. Immediately after workouts Research shows that taking a fast-digesting protein such as soy right after workouts boosts protein synthesis and muscle growth. Plus, soy’s antioxidant properties can enhance recovery. Take 20g of soy protein powder mixed with 20g of whey protein powder soon after training.


Soy protein obviously comes from the soybean. But soybeans aren’t pure protein — they contain a good amount of fat (albeit the healthy kind) and carbs. To produce a concentrated form of soy protein powder, the majority of these fats and carbs must be removed. Soy protein is typically manufactured from defatted soybean flakes or flour. You can find soy protein in powders in one or both of the following forms. 

SOY CONCENTRATE SC is usually about 70% protein, with the rest being carbs and fat. It is manufactured by placing soybean flakes or flour through either a water or alcohol extraction process to remove some of the carbs. Next, a drying and grinding process produces soy protein concentrate powder. It can cause gas in some people, due to the indigestible carbs it often contains.

SOY ISOLATE SI is made from soy concentrate that is further processed to remove most of the fat, carbs and gas-producing factors. It contains more than 90% protein.