Soy Protein or Whey?

In the bodybuilding community, the protein source of choice has long been whey, with soy protein coming in a distant second. Here is some information that may encourage you to take another look at soy.

The two most-researched forms of protein supplements are soy protein isolate and whey concentrate.

Soy protein isolate is 90 percent protein on a dry-weight basis, is highly digestible (97 percent) and allows the essential amino acids (valine, isoleucine and leucine, which the body does not produce) to be absorbed across the GI tract. A water-washed process is used to allow isoflavones to remain intact.

Both soy protein isolate and whey concentrate are high-quality proteins and have a Protein Digestibility Corrected Amino Acid Score (PDCAAS) of 1.0.

Glutamine, a nonessential amino acid, is the body's primary carrier of nitrogen to skeletal muscle and other tissues. It helps buffer lactic acid buildup in the blood and muscles, boosts muscle protein activity, increases growth hormone levels and strengthens immune capacity. Soy protein isolate typically contains 10.5 grams glutamine/100 grams protein, while whey concentrate contains 4.9 grams glutamine/100 grams protein.

Arginine plays a key role in stimulating the release of anabolic hormones that promote muscle formation, reducing physiological stress, and maintaining a strong and healthy immune system. Soy protein isolate contains 7.6 grams arginine/100 grams protein and whey concentrate contains 2.9 grams arginine/100 grams protein.

Branched chain amino acids are used as an energy source during exercise. During endurance activity, nitrogen is removed from the BCAA and converted to alanine, which is transported via the bloodstream from the muscle to the liver where it is converted to glucose.

Glucose from the liver returns to muscle to supply energy for fueling exercise. Whey concentrate contains approximately 20 percent BCAAs while soy protein isolate contains 18 percent.