Protein Quality Scores: DIAAS vs PDCAAS Explained for Lifters

DIAAS vs PDCAAS is a question about how we score protein quality. DIAAS (digestible indispensable amino acid score) is the newer FAO method: it rates each essential amino acid after digestion and has no ceiling. PDCAAS is the older one: it uses whole-gut digestibility and caps every score at 1.0. Animal proteins like whey, egg and casein tend to score higher on DIAAS, while many single plant proteins score lower, but the muscle-building gap is much smaller than the numbers suggest when total protein is enough.

This guide is part of our complete protein guide for hypertrophy. Here we stay on the scoring itself: what the numbers mean, where they mislead, and how to use them on an Indian plate.

Why 30 g of lentil protein is not the same as 30 g of whey

The question usually starts in the gym. You see “30 g protein” on a scoop of whey and “30 g protein” worth of dal, and both look equal on a tracker. They are not equal in what your body does with them.

Two things differ. First, amino acid makeup: how much of each essential amino acid the food carries per gram of protein. Second, digestibility: how much of that actually gets absorbed rather than lost. Protein quality scores try to roll both into one number.

That number is useful. It is also easy to over-read. Keep both in mind as we go.

What is PDCAAS and where does it fall short?

PDCAAS (protein digestibility-corrected amino acid score) was adopted by FAO/WHO as the preferred method for protein value in human nutrition. It compares the first limiting essential amino acid in a food with a reference pattern based on the needs of a preschool child, then corrects for true fecal digestibility (Schaafsma, 2000).

That review raised three problems:

• Fecal digestibility overestimates value. Amino acid nitrogen that reaches the colon is lost for protein synthesis and partly excreted as ammonia, so ileal digestibility (measured at the end of the small intestine) is the better correction.
• Truncation at 100%. Values above 1.0 are cut back, which is defensible only when a protein is the sole protein source in the diet. In mixed diets, truncation hides how much a strong protein can lift a weak one.
• The reference pattern came from limited data on preschool children’s requirements.

Think of it as a school exam where the top mark is capped at 100. A student who got 140 and a student who got 100 look identical.

What is DIAAS and how is it different?

DIAAS came out of a 2011 FAO expert consultation. It keeps the amino acid scoring idea but changes the digestion step. A 2024 review describes the shift: each indispensable amino acid is treated individually, using true ileal digestibility, and scores are not truncated (Moughan and Lim, 2024). The authors conclude DIAAS is currently the most accurate score for routinely rating single-source proteins.

The practical difference shows up most in plant foods. One pig-model study scored four animal and four plant proteins both ways. When the same scoring pattern was used, PDCAAS-like values were higher than DIAAS for skimmed milk powder, pea protein concentrate, soya protein isolate, soya flour and wheat, which suggests the older method may overestimate their quality (Mathai et al., 2017). Whey isolate, whey concentrate and milk protein concentrate had higher ileal digestibility for most essential amino acids than skimmed milk powder and the plant sources tested.

Protein bioavailability ranking: which foods score highest?

Scores vary by study, by the species used for digestibility testing and by the age reference pattern. So treat any ranking as a band, not a fixed number.

One 2020 overview pooled published amino acid and ileal digestibility data for five animal and 12 plant proteins, using the FAO pattern for children aged 0.5-3 years. On average (Herreman et al., 2020):

• Pork meat, casein, egg and potato protein scored above 100 (“excellent”).
• Whey and soy proteins scored 75 or above (“high”).
• Gelatin, rapeseed, lupin, canola, corn, hemp, fava bean, oat, pea and rice proteins scored below 75 (“no quality claim”).

The same paper found considerable variation within the same protein source, so a single food can land in different places depending on the dataset. A caveat on this source: its authors work for a potato protein company, which is worth knowing when reading a result that flatters potato.

Notice that the “excellent” tier includes a plant (potato protein), and soy sits next to whey. The line is not simply animal versus plant. It is closer to “which specific protein, and how is it processed.”

Does a lower DIAAS mean less muscle?

Not by as much as you would fear. This is where the scoring system meets real training results.

Human digestion data. In a randomized trial with 15 healthy adults fitted with naso-ileal tubes, real ileal amino acid digestibility was 93.6% for pea protein isolate and 96.8% for casein, with no significant difference. Leucine, valine, lysine and phenylalanine were less digestible in pea. The DIAAS was 1.00 for pea and 1.45 for casein, and net postprandial protein utilization was similar (Guillin et al., 2022). One caveat: two co-authors work for Roquette, a pea protein manufacturer, and the study tested a single pea isolate in a small group.

Muscle outcomes. A 2025 meta-analysis of 30 randomized trials found plant protein produced slightly lower muscle mass than animal protein (SMD -0.20, 95% CI -0.37 to -0.03). The effect was larger in adults under 60 and not seen in older adults. Soy versus milk protein showed no difference across 17 trials, while animal protein beat non-soy plant proteins (rice, chia, oat, potato) in 5 trials. Strength and physical performance did not differ. The authors say the effect is small and that a wider range of plant proteins needs testing (Reid-McCann et al., 2025).

A direct training trial. In 44 young, untrained men doing supervised resistance training three times a week for 12 weeks, a soy-and-pea blend (45 g/day) and whey (45 g/day) both improved lean mass, muscle cross-sectional area and leg-press strength, with no between-group differences (Santini et al., 2025). The trial was funded by a plant-based food company, and the participants were untrained, so it may not transfer fully to advanced lifters.

Putting those together: the evidence points to a small edge for animal protein that is clearest against non-soy single plant proteins, and nearly disappears with soy, blends and enough total protein. Because the trials differ in who they studied and which plant proteins they used, treat the exact size of the gap as uncertain.

Are there downsides to DIAAS?

Yes, and a fair article should say so. Critics argue DIAAS has limits, especially for plant-based eating (Craddock et al., 2021):

• It is built mostly on fast-growing animal models (often pigs) rather than humans.
• Many commonly eaten plant foods are not represented in the scoring data.
• It can underrate the improved digestibility of heat-treated or processed plant foods.
• It scores isolated foods, not the food matrix or a whole meal.
• It is sometimes used outside its intended context, including exercise settings.

The reviewers go as far as saying DIAAS should ideally be avoided when studying protein quality in plant-based diets. Others, including the 2024 review above, see it as the best routine tool we have, while noting that cooking and processing effects need more data (Moughan and Lim, 2024).

So what do we do with two opposing views? Use DIAAS as a screening tool for single foods. Do not treat it as a final ruling on a plate.

How vegetarians and plant eaters can close the gap

Here is the practical part. The goal is not to chase a perfect score. It is to cover amino acid gaps and total grams.

1. Eat enough total protein first. The simplest compensation for a lower-scoring protein is a bit more of it. Our protein calculator gives a starting number for your body weight and goal, and our optimal daily protein intake meta-analysis explains the range.
2. Mix sources. Modelling in the Herreman paper found potato, soy and pea proteins can complement a broad range of other plant proteins and raise the mixture’s DIAAS at specific ratios (Herreman et al., 2020). That is a model, not a trial in lifters, but it matches basic food logic.
3. Pair pulses with cereals. Cereals such as rice and wheat tend to be lower in lysine, and pulses tend to be lower in methionine. Dal with rice, rajma with roti, or chana with a curd side covers more ground than any of them alone. You do not need to match them perfectly at one meal.
4. Lean on soy and dairy. Soya chunks, tofu, paneer, curd, milk and whey sit at the stronger end for vegetarians. If you eat eggs, they score well too.
5. Consider a blend. If you use powder, a soy-pea or similar blend performed like whey in the 12-week trial above. See our guide to vegan protein powder blends for how to pick one.

If you are choosing between whey forms, our whey protein comparison covers concentrate, isolate and hydrolysate. For the direct plant versus animal question in more depth, see plant vs animal protein for hypertrophy. And because amino acid content matters, the leucine threshold explained is a useful companion read.

Quick comparison: PDCAAS vs DIAAS

Feature	PDCAAS	DIAAS
Digestibility used	Whole-gut (fecal) protein	Ileal, per amino acid
Cap on score	Truncated at 1.0	No cap
Scoring unit	First limiting amino acid	Each essential amino acid scored
Tends to overstate quality?	Yes, per reviews and the Mathai data	Less so, but animal-model limits remain
Best used for	Legacy labels and regulation	Comparing single proteins

Mistakes people make with protein quality scores

• Comparing one number across studies. Pig data, human data and different age patterns give different values for the same food.
• Ignoring total protein. Hitting your daily target matters more than shaving points off a score.
• Skipping the plate. DIAAS rates single foods, but you eat meals. Mixed meals behave differently from isolated proteins.
• Panic-buying isolated powders. A varied diet with enough protein covers most people. Powder is for convenience, not a requirement.

When to talk to a doctor or dietitian

If you have kidney disease, are pregnant, are managing a medical condition, or are an older adult with unintentional weight loss, get personalised advice before changing your protein intake significantly. Protein needs differ in those groups, and this article is general education, not medical advice.

The bottom line

DIAAS is a better yardstick than PDCAAS for comparing single proteins, because it uses ileal digestibility and does not cap scores. Animal proteins and some plant proteins like soy and potato score well, while many single plant proteins such as pea, rice and oat score lower. That gap matters most when protein is low, and it shrinks with enough total protein, varied sources and soy or blends. Pick your target, spread your sources, and let the plate do the work. Our free diet plan is a good place to see how that looks in practice.