Soybean protein is a "complete protein" since it provides all of the essential amino acids for human nutrition.[22][23] Soybean protein is essentially identical to that of other legume pulses (that is to say, legume proteins in general consist of 7S and 11S storage proteins), and is one of the least expensive sources of dietary protein.[24] For this reason, soy is important to many vegetarians and vegans.
Soy flour contains 50% protein.[25]
The digestibility of some soyfoods are as follows: steamed soybeans 65.3%, tofu 92.7%, soy milk 92.6%, and soy protein isolate 93–97%.[26][27] Some studies on rats have indicated the biological value of soy protein isolates is comparable to animal proteins such as casein if enriched with the sulfur-containing amino acid methionine