Soyabeans are the richest plant source of protein. They contains 38-43 percent protein as compared to other legumes which contain 18 to 25 percent protein. Soy protein is also of the highest quality amongst all legumes.
Under guidelines adopted by the Food and Drug Administration and the World Health Organization for evaluating protein quality for children and adults, soy protein isolate receives a rating of 1, which is the highest possible score. This means that the quality of soy protein is equal to that of meat and milk proteins.
Most plant proteins are considered “incomplete” proteins because they are low in one or more essential amino acids. Levels of one amino acid or another are insufficient for human needs. Grains are typically low in lysine; beans are typically low in the sulfur amino acids, methionine and cysteine. However, the level of sulfur amino acids in soybeans is higher than in other beans, and therefore soy protein is equivalent to animal protein in quality.
The World Health Organization (WHO) and the US Food and Drug Administration use an alternative method for evaluating protein quality called the protein digestibility corrected amino acid score (PDCAAS). The PDCAAS for soy protein isolate is 1.0, which makes soy equivalent to animal proteins in quality and higher than other plant proteins foods.
Soya foods if used smartly contribute significantly towards meeting protein needs, and could be an excellent addition to a diet for a variety of reasons.