Glossary

DIAAS & PDCAAS – Protein Quality Explained

Protein Quality Digestion Nutrition

How well proteins actually land: DIAAS uses ileal digestibility of individual EAAs; PDCAAS uses fecal overall digestibility and truncates at 1.0. Practical guardrails for hardgainers.

Notice

This page provides context and guardrails. It is not individual medical, nutrition, or training advice. Suitability and tolerance are individual; for pre-existing conditions, pregnancy/lactation, or medication, consult qualified professionals.

What do the acronyms mean?

  • DIAAS = Digestible Indispensable Amino Acid Score — assesses how many indispensable amino acids from a protein are actually absorbed in the small intestine (ileal).
  • PDCAAS = Protein Digestibility Corrected Amino Acid Score — older method using the most limiting amino acid and fecal digestibility; values above 1.0 are truncated to 1.0.
Hint

Both systems rate the quality of protein sources and help interpret biological value & usability.

Concept & System Placement

Short take Protein quality describes how efficiently a source provides indispensable amino acids and how well they’re digested/absorbed.

  • PDCAAS: Most limiting amino acid × fecal overall digestibility; values >1.0 are truncated.
  • DIAAS: Ileal digestibility of each EAA (absorption in the small intestine); no truncation >100.
  • Practice: Animal proteins (whey, casein, egg) often DIAAS ≈100–115; plant proteins benefit from blends (e.g., pea+rice).
Hint

Related basics: Protein, Leucine Threshold, MPS & MPB.

Mechanisms & Differences (at a glance)

  • Where it’s measured: PDCAAS = colon (bacterial fermentation can skew) · DIAAS = small intestine (ileal; closer to true absorption).
  • Resolution: PDCAAS averages across the whole protein · DIAAS scores each indispensable amino acid.
  • Scale: PDCAAS capped at 1.0 · DIAAS allows scores >100 (e.g., whey isolate).
  • Takeaway: For formulation/nutrition, DIAAS offers the more precise decision basis.

Typical Orientation Values

Protein sourceDIAASPDCAAS
Whey isolate≈ 110–1151.00 (truncated)
Casein≈ 1001.00 (truncated)
Egg≈ 1001.00 (truncated)
Beef≈ 90–95~0.9–1.0
Soy≈ 85–951.00 (truncated)
Pea≈ 65–75~0.7–0.8
Rice≈ 55–65~0.6
Wheat≈ 40–50~0.4–0.5

Values are rounded and depend on source/processing; they serve as orientation, not a rigid ranking.

Practice Guardrails for Hardgainers

  • Primary anchors: Whey/casein/egg (DIAAS ≈100+) to anchor meals with high MPS yield.
  • Plant smart: Pea+rice (complementary) — close EAA gaps; check tolerance.
  • Timing: Aim for 2–3 g leucine & a complete EAA profile per meal for maximal MPS trigger.
  • Think systemically: Protein quality feeds into TDEE efficiency and Rate of Gain — use maintenance & BMR as references.
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Safety

Tolerance is individual. With allergies/intolerances, check formulation/source; for medical conditions, seek clearance first.

MYTH

“Soy at 1.0 (PDCAAS) = as good as whey”

Oversimplified. PDCAAS truncates at 1.0 and can mask differences. DIAAS reveals limitations in the EAA profile and ileal digestibility. Practice: soy can be useful, but animal proteins typically show higher DIAAS; plant combos (pea+rice) improve the overall profile.

Directly related

Note: Descriptive information for orientation; individual adjustments may be useful or necessary.

Notice

Descriptive information for orientation — not a treatment, diet or training prescription. Individual differences and possible contraindications apply.

© Hardgainer Performance Nutrition® • Glossary • Updated: 31.10.2025