PDCAAS

PDCAAS, or Protein Digestibility-Corrected Amino Acid Score, is a method for evaluating the quality of dietary proteins for humans. It combines the essential amino acid composition of a protein with information about its digestibility to indicate how well the protein can meet human essential amino acid requirements.

Calculation: For a given protein, first determine the amino acid score by comparing the amount of each essential amino acid in the protein to the FAO/WHO reference pattern for adult humans; the limiting amino acid yields the lowest ratio. This amino acid score is multiplied by the protein’s true fecal digestibility. The resulting product is truncated to a maximum of 1.0, so that a protein cannot score above 1.

Use and interpretation: A PDCAAS of 1.0 indicates a protein that provides all essential amino acids in amounts meeting human requirements, given its digestibility. Values below 1 reflect a shortfall in one or more essential amino acids, or reduced digestibility.

Data and limitations: PDCAAS relies on data from digestibility studies, often using animal models to estimate human digestibility, and it uses fecal rather than ileal digestibility. It also uses a single reference pattern and caps the final score at 1.0, which can mask differences in amino acid balance between proteins. It may not reflect variations among individuals or meal context, and anti-nutritional factors can influence real-world value.

Relation to other methods: DIAAS, proposed by FAO as an alternative, uses ileal digestibility and does not cap at 1.0, offering a potentially more accurate assessment of protein quality. PDCAAS remains in use in some labeling and regulatory contexts and provides a simple, if imperfect, standard for comparing dietary proteins.