Soy Nutrition Institute
Back to In the News

Jun 01, 2014

More educated needed about the Protein Digestibility Corrected Amino Acid Score

In 1991, the Joint FAO/WHO Expert Consultation on Protein Quality Evaluation recommended adopting the protein digestibility corrected amino acid score (PDCAAS) as the assay of choice for evaluating protein quality.3 This assay determines protein quality by comparing the amino acid content of a protein with the reference pattern for indispensable amino acids (IAAs) and correcting for digestibility. This PDCAAS has become the standard method for protein quality evaluation in the United States. In 1993, the US Food and Drug Administration adopted it for nutrition labeling of proteins in foods.


However, a recent survey of dietitians in Missouri reported that few dietitians can correctly identify the PDCAAS as the accepted assay for evaluating protein quality. In fact, only 18% of the respondents were familiar with this method and only 10% correctly identified it as the method used by the FDA for nutrition labeling. On the positive note, 97% of the respondents correctly identified wheat and rice as incomplete proteins although 25% of the respondents incorrectly identified peanut protein as complete and 27% were not able to identify soy protein as a complete protein. Extensive work published in 2011 shows the quality of soy protein products (soy protein concentrate and isolated soy protein) to be similar to animal protein.


Hughes GJ, Kress KS, Armbrecht ES, et al. Initial investigation of dietitian perception of plant-based protein quality. Food Sci Nutr. 2,371-9 (2014).