DIAAS & PDCAAS
- Protein quality
- Digestion
- Nutrition
By Mag. Christian Schönbauer, founder of Hardgainer Performance Nutrition®. Training since 1999, started under 50 kg.
DIAAS and PDCAAS are two scoring systems for protein quality: they show how well a protein covers your need for indispensable amino acids once digestion has taken its share. For a hardgainer (hard gainer), DIAAS vs PDCAAS is not a lab question. It tells you which protein source actually delivers per meal and which one only looks good on paper.
Note
This page gives you context and guardrails, not individual medical or nutrition advice. If you have a medical condition or take medication, please get it checked by a doctor.
What is DIAAS and PDCAAS? The definition in 20 seconds
Both scores compare the amino acid profile of a protein with human requirements and correct for digestibility. PDCAAS has been in use since 1991. In 2011 an FAO expert consultation rated DIAAS as the better method. The difference comes down to three things: where it measures, how fine it measures and whether the score is capped.
- PDCAAS: Protein Digestibility Corrected Amino Acid Score. Measures the digestibility of the whole protein from faecal analysis and caps the result at 1.00.
- DIAAS: Digestible Indispensable Amino Acid Score. Measures at the end of the small intestine, for each indispensable amino acid separately, and does not cap.
- For hardgainers this means: Protein quality is fine-tuning. Calories, daily amount and distribution come first, the best source comes after.
The anchors in the system: protein, the leucine threshold per meal and muscle protein synthesis (MPS).
DIAAS vs PDCAAS: the difference at a glance
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 |
|---|---|---|
| Where it measures | from faecal analysis, after the large intestine | at the end of the small intestine, where absorption happens |
| What it measures | digestibility of the whole protein | digestibility of each indispensable amino acid separately |
| Upper limit | capped at 1.00 | not capped, values above 1.00 are possible |
| In use since | 1991 | rated superior by the FAO in 2011 |
| Weakness | overrates weaker proteins, and the cap makes good sources look identical | hard to determine, many foods still lack human data |
The difference that matters most day to day is the cap. On PDCAAS every good source lands on 1.00 and looks equivalent. DIAAS shows the spread: in a rat study scores ranged from 0.01 for a corn-based breakfast cereal to 1.18 for milk protein concentrate. Many tables multiply that by 100, so 118.
The second difference is where it measures. Whatever only disappears in the large intestine does not reach your muscle as amino acids. PDCAAS still counts it as digested, DIAAS does not. That is why weaker proteins usually score higher on PDCAAS than DIAAS shows.
DIAAS table: what the studies show
There is no finished list with fixed values for every food. Scores depend on the product, processing and method. This table shows what the two comparison studies on this page actually measured.
| Protein source | Result | Model |
|---|---|---|
| Milk protein concentrate | DIAAS 1.18, the highest of 14 sources tested | Rats |
| Whey isolate, whey concentrate | higher digestibility of most indispensable amino acids than skim milk powder, pea, soy and wheat | Pigs |
| Soy isolate | more digestible than soy flour, still overrated by PDCAAS | Pigs |
| Pea protein concentrate | overrated by PDCAAS | Pigs |
| Skim milk powder | overrated by PDCAAS, so animal protein is not automatically top tier | Pigs |
| Whole-grain wheat | lowest digestibility of almost all indispensable amino acids, overrated by PDCAAS | Pigs |
| Corn-based breakfast cereal | DIAAS 0.01, the lowest of 14 sources tested | Rats |
As practice orientation, not a label: dairy proteins sit at the top, soy behind them, grains at the bottom. Processing shifts the numbers, soy isolate did better than soy flour.
Practice: the 14-day check
- Day 0, note where you stand: Which protein source carries each of your meals? Mark the meals that rest only on grains or a single plant source.
- Document daily: Morning bodyweight, meals with a solid protein anchor yes or no, and steps as your measure for NEAT. How much your steps burn is shown by the NEAT Calculator.
- Day 14, check the trend: Upgrade the weak meals: add dairy, combine plant sources or go for a bigger portion. If your rate of gain is still flat, it is the calories, not protein quality.
The best source is the one you tolerate and actually get down every day.
Common misconceptions
- “Plant protein is just as good, PDCAAS 1.0 proves it.” The 1.00 is a ceiling, not a measurement. In the pig study, PDCAAS-like scores for soy isolate and pea came out higher than their DIAAS. In practice that does not mean giving up plant protein. It means bigger portions and combinations so you still clear the leucine threshold per meal.
- “Animal protein is always top tier.” Not automatically. Skim milk powder was overrated by PDCAAS too. Processing counts.
- “A higher DIAAS builds more muscle.” None of the studies measured that. Once calories and protein amount are right, the source is the final polish, not the lever.
- “Blends are just marketing.” Not by default. A blend of several sources can cover the weak spots of a single one. What counts is what is inside, not the word on the tub.
Protein is protein. If you eat enough grams, the source does not matter, and more is always the safer bet.
Past a certain point, more protein adds no extra muscle, it just pushes out calories. And not every gram counts the same: weaker sources deliver fewer indispensable amino acids than PDCAAS suggests. The answer is not a mountain of protein, it is enough protein per meal from a good source or a smart combination.
Common questions
What is the difference between DIAAS and PDCAAS?
PDCAAS measures the digestibility of the whole protein from faecal analysis and caps the value at 1.00. DIAAS measures the digestibility of each indispensable amino acid at the end of the small intestine and does not cap. As a result DIAAS shows differences that PDCAAS flattens out.
What does PDCAAS mean?
PDCAAS stands for Protein Digestibility Corrected Amino Acid Score. It has been in use since 1991 and 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. In 2011 an FAO expert consultation rated it superior to PDCAAS. It measures at the end of the small intestine and treats every indispensable amino acid separately.
3 more questionsShow less
Which protein source has the highest DIAAS score?
In the studies on this page, milk protein concentrate came out on top, with 1.18 as the highest of 14 sources tested in rats. In pigs, whey isolate and whey concentrate showed higher amino acid digestibility than soy, pea and wheat. Dairy proteins sit at the top, grains at the bottom.
Is there a DIAAS calculator?
There is no meaningful everyday calculator. DIAAS is determined in a lab from amino acid composition and digestibility at the end of the small intestine. What you actually need is a rough ranking 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 your daily total, a better source changes nothing. Only once calories, amount and several protein meals are in place does upgrading quality pay off.
From term to practice: your tools
Protein quality only works once calories, amount and distribution are in place. These three tools give you the numbers for that.
See all Hardgainer Tools. If you want more out of your numbers, go with Hardgainer Pro.
What the research says
Three papers behind the claims on this page
Why DIAAS is meant to replace PDCAAS is well documented. These three papers are behind the claims above.
- Untruncated PDCAAS values were generally higher than DIAAS values, especially for poorer proteins. DIAAS ranged from 0.01 for a corn-based breakfast cereal to 1.18 for milk protein concentrate. Growing male rats, 14 protein sources, 6 animals per test diet. Faecal digestibility differed from digestibility at the end of the small intestine for 11 of the 14 sources, by 10 percent on average. Rutherfurd et al., The Journal of Nutrition, 2015
- For skim milk powder, pea protein concentrate, soy isolate, soy flour and whole-grain wheat, PDCAAS-like values were higher than DIAAS, so the quality of these proteins is overestimated. Pig study with four animal and four plant proteins. Whey isolate, whey concentrate and milk protein concentrate had the highest digestibility of most indispensable amino acids, wheat the lowest. Mathai et al., The British Journal of Nutrition, 2017
- An FAO working group considers DIAAS the conceptually better method, but there is not yet enough human data on amino acid digestibility. Methods paper from the 2014 working group. PDCAAS has been used since 1991, and an FAO expert consultation rated DIAAS superior in 2011. The group proposes 5 research protocols. Lee et al., The Journal of Nutrition, 2016
What the studies do not cover
Both comparison studies were done in animals, rats and pigs, not humans. The scores apply to the products tested and shift with processing. None of the three papers measured whether higher protein quality adds more muscle once total intake is sufficient.
Your takeaway: a PDCAAS of 1.00 does not mean equivalent. Calories, amount and distribution first, then the source, and combine plant sources.
One clear mission every week.
Not a newsletter, a weekly mission. One focus, three concrete steps, five days of execution. Plus new drops before anyone else.
Hardgainer Hacks™ right after you confirm. 10 strategies for real mass gain, straight to your inbox.
After signing up you get a confirmation email (double opt-in). Click it, otherwise nothing can be sent. Every issue published so far is in the Briefing Archive. Details on data processing in the privacy policy.
Reading & Resources
The terms directly around protein quality and the pillars next to it.
Content here is general practice guidance and does not replace individual medical or nutritional advice.
