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Protein quality scores: PDCAAS and DIAAS explained
Not all protein sources are scored equally — these two methods are how nutrition science formally measures protein quality.
PDCAAS (Protein Digestibility-Corrected Amino Acid Score) and its successor DIAAS (Digestible Indispensable Amino Acid Score) are methods for scoring how well a protein source meets essential amino acid needs, adjusted for how digestible it actually is. Both compare a food's essential amino acid profile against a reference pattern of human requirements.
- Whey, egg, and milk protein score at or near the maximum on both scales — highly digestible, complete amino acid profiles
- Soy protein scores well, among the highest of common plant proteins
- Most other plant proteins (wheat, rice, beans individually) score lower, usually due to being relatively low in one or more essential amino acids — which is why combining varied plant protein sources across the day matters more on a plant-based diet
DIAAS is generally considered the more accurate, updated method, but PDCAAS still appears widely in food labeling and older research.
Keep reading: Complete vs. incomplete protein · Plant-based protein sources · Protein powder 101