Is soy protein as effective and beneficial for building muscle as whey protein? 

Both plant-based soy protein and whey protein from dairy milk have been shown to help build and maintain lean body mass. Although not as rapidly digested and absorbed by the body as whey protein, soy protein does help support lean muscle mass.

For many years, a score called Biological Value was used to measure the quality of protein. Whey generally scored much higher than soy because of its unique composition. However, current research shows a more appropriate measure called the Protein Digestibility Corrected Amino Acid Score (PDCAAS). Both soy and whey have a PDCAAS score of 1.0.