PDCAAS (Protein Digestibility Corrected Amino Acid Score) is thought to be the most reliable tool for evaluation of protein quality, or rather an index showing how useful are various protein sources for humans.
PDCAAS has been adopted by both WHO (World Health Organization) and the American FDA (Food and Drug organization).
Proteins are evaluated according to the formula: (mg of limiting amino acid in 1 g of test protein / mg of same amino acid in 1 g of reference protein) x fecal true digestibility percentage.
“Limiting amino acid” is the essential amino acid which is represented in the given protein source in lower amounts than the recommended intake by humans. It means that a protein completely lacking one or more essential amino acids will always have a score of 0.
“Fecal true digestability” means how much of the protein has been really digested and what part has been secreted from the body. It should be noted that the digestion of a child between 2-5 years of age is used in PDCAAS – the score has been created to evaluate the best sources of protein for malnourished children.
1.00 egg white
1.00 soy protein
0.75 black beans
0.70 other legumes
0.59 cereals and derivatives
0.42 whole wheat
Comparison between the BV (Biological Value) and PDCAAS
PDCAAS is considered superior method in comparison to BV and PER (Protein Efficiency Ratio) because it takes into account digestability (unlike BV) and works with human requirements (unlike PER which is based on observation of rats).
Usefulness for athletes
PDCAAS is a method developed for evaluation of the needs of normal children, not hard-training athletes. Therefore all protein sources with score over 1,00 have been leveled down to exactly 1. What does it mean? It means that the score of 1 is perfect for the needs of an average person. If the protein is very rich in all essential amino acids (more than the requirements of average person), PDCAAS sees no added value in such food and just considers it “sufficient”.
Therefore we have several proteins with the score of 1, although their usefulness in sports is probably quite different.