Both soy protein and whey protein are complete proteins, meaning they contain all the essential amino acids required to build new tissues in the body. The PDCAAS of both is 1.0 (the highest score for protein quality and digestibility) making these protein sources of superior value for quality lean muscle gains.
 
However, some formulations of soy protein, such as Supro® brand soy protein, contain superior levels of arginine, glutamine, leucine, isoleucine and valine - five critical-cluster amino acids which have a vital role in preserving muscle size and density. This makes soy protein an excellent addition to the armoury for bodybuilders. Using soy protein is also a great complete protein option for vegans or dairy intolerant individuals.