DIAAS & PDCAAS
DIAAS and PDCAAS are not “bro opinions”. They are scoring systems for protein quality. The difference matters: measurement site, resolution, and capping. For hardgainers (hard gainer), this is useful because you can spot faster which protein source actually delivers per meal.
Note
This page gives context and guardrails. It is not individual medical, nutrition or training advice. If you have a pre-existing condition or take medication, that question belongs with a qualified professional.
What do DIAAS and PDCAAS mean?
- DIAAS = Digestible Indispensable Amino Acid Score. Uses ileal digestibility per essential amino acid (small intestine).
- PDCAAS = Protein Digestibility Corrected Amino Acid Score. Uses fecal digestibility and caps values at 1.0.
In plain terms: PDCAAS can be useful, but it is coarse. DIAAS is usually the sharper lens when comparing protein sources.
PDCAAS vs DIAAS: the difference at a glance
DIAAS vs PDCAAS is the most common question on the topic. Both rate protein quality, but they measure in different places and calculate differently. That is why the same protein source ends up with two different grades.
| Criterion | PDCAAS | DIAAS |
|---|---|---|
| Full name | Protein Digestibility Corrected Amino Acid Score | Digestible Indispensable Amino Acid Score |
| Where it measures | at the end of the large intestine, from faecal analysis | at the end of the small intestine, where absorption actually happens |
| What it measures | digestibility of the whole protein | digestibility of each individual indispensable amino acid |
| Upper limit | truncated at 1.00 | not truncated, values above 100 are possible |
| Introduced | 1991 by FAO and WHO | 2013 by the FAO as the successor |
| Weakness | gut bacteria alter the amino acids, which inflates the value. Truncation makes high-quality sources indistinguishable | harder to determine, so many foods still have no published value |
The practically most important difference is truncation. PDCAAS caps at 1.00. Whey isolate, casein, egg and soy all sit at 1.00 and therefore look equivalent. DIAAS does not cap and shows the spread: whey sits above 100, soy below.
The second difference is the measuring point. Whatever the large intestine still breaks down no longer reaches the muscle. PDCAAS counts it anyway, DIAAS does not. That is why plant sources usually drop further on DIAAS than PDCAAS would suggest.
Mechanisms and key differences
- Measurement site: PDCAAS measures “at the end” (feces). DIAAS measures in the small intestine, closer to actual absorption.
- Resolution: PDCAAS averages the whole protein. DIAAS evaluates each essential amino acid separately.
- Capping: PDCAAS caps everything above 1.0. DIAAS can be >100 on purpose.
- Practical consequence: PDCAAS can hide meaningful differences. DIAAS shows limitations more clearly.
Seven rules you can actually use
- Rule 1: Use DIAAS for “fine decisions” (source vs blend). Use PDCAAS only as a rough compass.
- Rule 2: Animal proteins are often “easy mode”. Plant-based can work, but more often via smart combinations.
- Rule 3: Processing matters. Heat, extraction, and fermentation can change digestibility.
- Rule 4: Think in meals, not only daily totals. Each meal should deliver a full essential amino acid profile.
- Rule 5: Blends are not automatically marketing fluff. Good blends fix limiting amino acids.
- Rule 6: Tolerance wins. The “best” protein is useless if you cannot stick to it.
- Rule 7: Priorities stay boring: get calories and total protein consistent first, then fine-tune with DIAAS.
DIAAS table and PDCAAS score: typical values
| Protein source | DIAAS | PDCAAS |
|---|---|---|
| Whey isolate | ≈ 110 to 115 | 1.00 (capped) |
| Casein | ≈ 100 | 1.00 (capped) |
| Egg | ≈ 100 | 1.00 (capped) |
| Beef | ≈ 90 to 95 | ≈ 0.9 to 1.0 |
| Soy | ≈ 85 to 95 | 1.00 (capped) |
| Pea | ≈ 65 to 75 | ≈ 0.7 to 0.8 |
| Rice | ≈ 55 to 65 | ≈ 0.6 |
| Wheat | ≈ 40 to 50 | ≈ 0.4 to 0.5 |
These are rounded ranges and depend on the specific food, processing, and study method. Use them as a compass, not a religion.
Practical guardrails for hardgainers
- Anchor per meal: A high-quality source makes it easier to hit the MPS trigger. Start here: Protein.
- Leucine as a shortcut: If you consistently hit it per meal, a lot becomes easier. Start here: Leucine threshold.
- Understand the mechanism: If you want the “trigger” in plain terms: MPS and MPB.
- Fine-tune when basics are stable: Creatine is a good example of “works, but does not replace basics”.
Soy has a PDCAAS of 1.00, just like whey. So both are equivalent and the source does not matter.
The 1.00 is a ceiling, not a measurement. PDCAAS truncates there, which is why every good source looks identical. On DIAAS whey isolate sits around 110 to 115 and soy around 85 to 95. In practice that does not mean avoiding plant protein, it means using more of it and combining sources so the leucine threshold per meal still gets cleared.
Common questions
What is the difference between DIAAS and PDCAAS?
PDCAAS measures digestibility of the whole protein at the end of the large intestine and truncates the value at 1.00. DIAAS measures digestibility of each individual indispensable amino acid at the end of the small intestine and does not truncate. As a result DIAAS shows differences that PDCAAS flattens out.
What does PDCAAS mean?
PDCAAS stands for Protein Digestibility Corrected Amino Acid Score. FAO and WHO introduced it in 1991. It rates how well the amino acid profile of a protein covers human requirements, corrected for digestibility.
What does DIAAS mean?
DIAAS stands for Digestible Indispensable Amino Acid Score. The FAO proposed it in 2013 as the successor to PDCAAS. It measures at the end of the small intestine and treats every indispensable amino acid separately.
Does a PDCAAS of 1.0 mean a protein is as good as whey?
No. PDCAAS truncates at 1.00, which is why whey isolate, casein, egg and soy all reach that value. On DIAAS whey isolate sits around 110 to 115 and soy around 85 to 95. Truncation hides exactly that gap.
Which protein source has the highest DIAAS score?
Among common sources whey protein isolate and milk protein lead, with values around 110 to 115. Casein and egg follow around 100, beef at 90 to 95 and soy at 85 to 95. Pea, rice and wheat sit clearly below.
Is there a DIAAS calculator?
There is no meaningful everyday calculator, because DIAAS is determined in a laboratory from amino acid composition and ileal digestibility. What you actually need is a reference table and the rule to combine sources rather than optimise them.
How much does protein quality matter for hardgainers?
It matters, but it ranks behind amount and distribution. If you never hit the daily total, a better source changes nothing. Only once amount and distribution across four meals are in place does upgrading quality pay off.
From term to practice: your tools
Protein quality only works once amount and distribution are in place. Both take two minutes to work out.
What the research says
Four papers behind the claims on this page
Why DIAAS is meant to replace PDCAAS is well documented. Three papers carry the claims on this page.
- For dairy and plant proteins the DIAAS values differed from the PDCAAS values, and the ranking of sources shifted. Direct evidence that the two systems do not just scale differently but lead to different conclusions. Mathai et al., British Journal of Nutrition, 2017
- In an animal model PDCAAS and DIAAS described the protein quality of the same foods differently, particularly for plant sources. Shows the difference is systematic rather than a artefact of single measurements. Rutherfurd et al., Journal of Nutrition, 2015
- The FAO working group describes the methodology behind DIAAS and the open questions in determining it. The source for the caveat: for many foods no reliable DIAAS values exist yet. Lee et al., Journal of Nutrition, 2016
What the studies do not cover
The values in the table are reference figures pooled from several sources and depend on processing, variety and preparation. They are not laboratory values for a specific product. Part of the DIAAS data comes from animal models rather than humans. And none of these papers tested whether higher protein quality still adds measurable muscle once total intake is sufficient.
Practical takeaway: Quality comes after amount and distribution. If your daily total and four meals above the leucine threshold are in place, a better source collects the last few percent. If they are not, it collects nothing.
Protein quality understood. Now the system behind it.
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Reading & Resources
DIAAS and PDCAAS rate protein quality. Here is the main topic these terms belong to, plus the terms around them.
Main topic Nutrition for Hardgainers Surplus, energy density and distribution. The pillar where protein quality becomes a meal. To the main topicContent here is general practice guidance and does not replace individual medical or nutritional advice.
