Athletes and Consumers tend to ignore soy protein as they feel it is inferior to whey protein in terms of promoting lean body mass. It is a plant protein and usually plant proteins are considered to be incomplete protein due to lack of one or two essential amino acids, but we forget that soy stands out and is much superior to other plant proteins like pea protein or other pulse protein.
Soy Protein is prepared from the soybean plant from where we get tofu (vegan replacement of paneer – cottage cheese). Soybean is well established high in quality and superior among all plant proteins. Not only protein, but it is also a great source of antioxidants, fiber, calcium, B-complex vitamins, and zinc.
Understanding the Protein Quality of Soy
Apart from other ways of defining the quality of protein, PDCAAS is the one well studied now. Protein Digestibility Corrected Amino Acid Score (PDCAAS) is based on a comparison of the essential amino acid content of a test protein with that of a reference essential amino acid pattern and a correction for differences in protein digestibility as determined using a rat assay. PDCAAS 1 is considered to be an excellent source of protein. Soy and Whey both have PDCAAS value as 1.
From the above table, it is very clear that the protein quality of soy is much better as compared to other plant proteins like black beans, wheat gluten, and peanuts.
Apart from PDCAAS as a deciding factor for the quality of proteins, more recently, a new, ostensibly superior, method for estimating protein quality has been proposed called the digestible indispensable amino acid score or DIAAS.
Under DIAAS there is the recognition that amino acids are individual nutrients and that protein quality is contingent on Individual Amino Acids (IAA) content and ileal (as opposed to fecal) digestibility.
It is clear from the above image too that soy protein isolate has the highest DIAAS as compared to Pea and Rice Protein. Hence, it is a hero in both PDCAAS and DIAAS score and places well with the Whey Protein.