During the production of soy protein, soybeans are defatted and hulled to leave behind highly concentrated protein. Unlike many plant sources of protein, soybeans are complete proteins. This means they have sufficient amounts of the nine essential amino acids. These amino acids are considered “essential” because your body cannot produce them by itself. As a result, soy is a reliable source of protein for vegetarians.
Whey protein originates from whey, a byproduct of milk during cheese production. After whey has been separated, it is filtrated to a concentrated form of protein -- whey protein. Like soy protein, whey protein has all the essential amino acids. In fact, it is very high in branched chain amino acids, which are three essential amino acids that make up 30 percent of the essential amino acids found in skeletal muscle. Therefore, whey proteins supplements are effective for athletes who want to build more muscle mass.
While protein supplements help increase your protein intake for building muscle mass, not all supplements have the same quality of protein. Biological value and net protein utilization are common methods of measuring the quality of different sources of dietary protein. BV assesses the quality of dietary protein sources by considering the amount of protein your body absorbs from certain foods. NPU takes it a step further by also considering the amount of protein ingested or used by your body. Nutritional data from the U.S. Dairy Export Council suggests that whey protein has a considerably higher BV and NPU than soy protein. Thus, whey protein is more efficient than soy protein for building muscle.
Soy vs. Whey Protein
The quality of whey and soy protein has spurred an abundance of scientific research to determine their effect on muscle growth. In a 2009 study published by the “Journal of Applied Physiology,” researchers assessed the quality of various types of protein, including whey, soy and casein. The results showed that whey protein was more effective at stimulating protein synthesis or muscle growth than casein and soy. A 2007 study in the “American Journal of Clinical Nutrition” supports those results. Since whey protein has been proven to be absorbed more efficiently by your body and stimulate muscle growth more than soy protein, it is better for building muscle. However, if you are a vegetarian, soy protein is an ideal alternative to whey protein, because it also contains all the essential amino acids.