PDCAAS stands for Protein Digestibility Corrected Amino Acid Score. It's the standard method used by the World Health Organization and the FDA to evaluate protein quality. The score ranges from 0 to 1.0 (sometimes expressed as 0 to 100) and accounts for two things: whether the protein provides all essential amino acids in adequate amounts, and how well your body can actually digest and absorb those amino acids. A score of 1.0 means the protein meets all essential amino acid requirements and is highly digestible.
Why It Matters
PDCAAS gives you an objective way to compare protein sources. Whey, casein, egg, and soy all score 1.0 — the maximum. Whole beef scores about 0.92. Pea protein scores approximately 0.82 to 0.93, depending on the source and processing method. Rice protein is approximately 0.50 to 0.60. Collagen scores 0.0 because it completely lacks the essential amino acid tryptophan. These numbers explain why not all "25 grams of protein" labels are equivalent. A serving of whey with 25 grams of protein at a PDCAAS of 1.0 provides more usable amino acids than a serving of rice protein with 25 grams at a PDCAAS of 0.55.
What to Look For
Most protein supplement labels don't list the PDCAAS directly, but you can use the protein source to estimate it. Whey (isolate or concentrate), casein, egg white, and soy isolate are all 1.0 — the top tier. Pea protein is close behind, typically scoring 0.82 to 0.93 depending on processing. Blended plant proteins that combine complementary amino acid profiles typically score higher than either component alone. If a product lists collagen as its primary protein source, understand that despite potentially high protein grams on the label, the PDCAAS is 0.0 — it is not a substitute for a complete protein when muscle preservation is the goal.
For GLP-1 Medication Users
For GLP-1 users managing reduced food intake, PDCAAS offers a quick way to assess whether a protein source is pulling its weight. A protein with a PDCAAS of 1.0 (like whey or egg) means nearly everything you eat is being used. A score of 0.5 means you'd need to eat roughly twice as much to get the same usable protein. When every bite counts, prioritizing high-PDCAAS sources is one of the simplest strategies for meeting your protein targets.
Related Terms
Bioavailability
How efficiently your body absorbs and uses protein from a given source. Higher bioavailability means more of what you eat actually reaches your muscles and tissues.
Complete Protein
A protein source that contains all 9 essential amino acids in adequate amounts for human needs. Most animal-based proteins are complete; many plant proteins are not.
Collagen
A structural protein that supports skin, joints, hair, and connective tissue. Important: collagen is NOT a complete protein — it scores 0.0 on the PDCAAS scale and cannot replace whey or other complete proteins for muscle building.
Amino Acids
The building blocks of protein. There are 20 amino acids total, and your body needs all of them to build and repair tissue — but 9 of them, called essential amino acids, must come from food.