DIAAS vs. 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
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.
Concept and 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).
Mechanisms and 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 source | DIAAS | PDCAAS |
|---|---|---|
| Whey isolate | ≈ 110–115 | 1.00 (truncated) |
| Casein | ≈ 100 | 1.00 (truncated) |
| Egg | ≈ 100 | 1.00 (truncated) |
| Beef | ≈ 90–95 | ~0.9–1.0 |
| Soy | ≈ 85–95 | 1.00 (truncated) |
| Pea | ≈ 65–75 | ~0.7–0.8 |
| Rice | ≈ 55–65 | ~0.6 |
| Wheat | ≈ 40–50 | ~0.4–0.5 |
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.
“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.
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