What DIAAS measures and why it replaces PDCAAS
The Digestible Indispensable Amino Acid Score (DIAAS) rates proteins by their content of the nine essential amino acids your body cannot make, adjusted for digestibility. Unlike an earlier metric (PDCAAS), DIAAS accounts for true absorption in your small intestine, not just digestibility in the test tube.
Animal proteins consistently score 0.9 to 1.0 because they contain all nine essential amino acids in the right ratios and are easily digestible. Eggs are the reference standard at 1.0. Most plant proteins score lower because they either lack one amino acid (beans lack methionine, grains lack lysine) or are harder for humans to digest fully.
Plant sources and protein combining
Isolated soy protein scores around 0.91, making it the only plant source that rivals animal proteins. Lentils and chickpeas score 0.6 to 0.7, beans range 0.5 to 0.7, and whole grains sit around 0.4 to 0.6. These lower scores reflect both amino acid imbalance and plant cell wall barriers that reduce absorption.
Pairing complementary proteins boosts overall quality. Rice and beans together provide all nine essential amino acids in adequate ratios, though the DIAAS of the mixture is lower than either pure animal source. Eating them in the same meal (not even the same day, contrary to older advice) allows your body to combine amino acids for protein synthesis.