Amino acids that move beyond the terminal ileum in the body are less likely to be absorbed for use in protein synthesis.
Similarly, amino acids that are lost due to antinutritional factors present in many foods are assumed to be digested according to the PDCAAS.
To arrive at the final result, all individual amino acids would have to be taken into account, though, so the PDCAAS of each constituent is largely useless.
Despite individual scores of 0, the combination of both in adequate amounts has a positive PDCAAS, with the limiting amino acids isoleucine, threonine, and methionine.
Further, according to a 2000 study by Gerjan Schaafsma, "The questions about the validity of the amino acid scoring pattern and the application of the true fecal rather than the true ileal digestibility correction, as well as the truncation of PDCAAS values warrant a critical evaluation of PDCAAS in its current form as a measure of protein quality in human diets.
[6][7] In addition, the fact that four proteins, all with different amino acid profiles, receive identical scores of 1.0 limits its usefulness as a comparative tool.
In short, this method, however, gives no distinction of their performance relative to each other, because after they pass a certain point, they are all capped at 1.0 and receive an identical rating.