Protein Quality Scores: PDCAAS vs DIAAS and How They Are Used on Labels
What PDCAAS and DIAAS protein quality scores measure, how they differ, how the US label rule uses PDCAAS, and why a score does not tell you whether a product suits you.
Content last updated . This page has not been medically reviewed.
How the two scores differ
| Feature | PDCAAS | DIAAS |
|---|---|---|
| Origin | Recommended by a joint FAO/WHO consultation in 1989 [1] | Recommended by the 2011 FAO consultation, report published 2013 [1] |
| Calculation | The limiting amino acid score is multiplied by protein digestibility [1] | A ratio is worked out for each indispensable amino acid, and the lowest value is the DIAAS [1] |
| Digestibility | One crude protein value over the whole digestive tract (faecal) [1] | True ileal (end of small intestine) digestibility of each amino acid, preferably in humans, otherwise growing pigs, then rats [1] |
| Cap at 100 percent | Values above 100 percent are truncated [3] | Not truncated, except for mixed diets or sole-source foods [1] |
| Reference pattern | Not covered in the sources we read | For regulation, the young-child pattern (6 months to 3 years) for all foods other than infant formula [1] |
FAO called single-value crude protein digestibility a shortcoming and judged that ileal digestibility better reflects the amino acid absorbed. [1] It also noted that truncation removes differences between high-protein foods such as milk and soya. [1] PDCAAS itself was described as having proved of considerable value in practice for some 20 years. [1]
Example values from the FAO report
These are FAO's own worked examples, using true ileal digestibility and the young-child pattern. They are not label values and will vary with batch and processing. [1]| Food (100 g) | Protein (g) | DIAAS | FAO's judged quality |
|---|---|---|---|
| Wheat | 11 | 40 | Low [1] |
| Peas | 21 | 64 | Low [1] |
| Whole milk powder | 28 | 122 | High [1] |
A low score for one food does not mean a mixed diet is low quality. DIAAS is calculated without reference to the meal it is eaten in, so it gives only a crude estimate of a protein's value in a mixed diet. [3] FAO also stated that quality cannot be substituted for quantity. [1] To see how plant and dairy proteins compare in practice, see Whey vs Plant Protein.
How the scores are used on labels
United States. Under FDA's regulation, a protein score below 20 percent for foods for adults and children 4 and over requires the words "not a significant source of protein" or a Percent Daily Value listing. [2] A Percent Daily Value for protein is optional, but must be given when a protein claim is made. [2] It is calculated from the actual protein multiplied by the digestibility-corrected amino acid score, capped at 1.00. [2] The Daily Value on US labels for protein is 50 g, based on a 2,000-calorie reference. [2]FAO's suggestion (not a rule). For claims such as "source" or "high" protein, FAO suggested DIAAS cut-offs, with examples of 100 or more as excellent or high and 75 to 99 as good or source. [1] It suggested that proteins below a cut-off should not get these claims. [1] It said the real cut-off values need further consideration. [1]
Other countries. How other countries' labels use these scores was not described in the sources we read. Check the rules where you live. For label reading, see Reading a Protein Powder Label.
Frequently asked questions
Is DIAAS better than PDCAAS?
FAO recommended DIAAS to replace PDCAAS because it uses ileal digestibility of each amino acid. [1] A 2024 review by its chair and a colleague calls it the most accurate routine score for single-source proteins. [3]
Why can DIAAS go above 100?
FAO advised not truncating DIAAS values, so a protein richer in amino acids than the reference can score over 100. [1]
Does my protein powder label show a PDCAAS?
Not necessarily. In the US, the regulation requires a protein score-based statement only in certain cases, such as a protein claim or a very low score. [2]
Does a higher score mean more muscle or better health?
Proper evidence not found in our search. The scores estimate amino acid supply, and FAO said quality cannot replace quantity. [1]
Who should be careful with protein products?
People with kidney disease should work with a dietitian or health care professional on the amount and type of protein. [4] Ask a clinician or pharmacist before starting any supplement if you take medicines or are pregnant.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Limits and uncertainty
- Data gaps. In 2011 FAO noted too few published ileal digestibility data for foods as eaten by humans. [3] Since then, numerous studies have reported pig-model values, and the pig assay's validity has been confirmed. [3]
- Authors' position. A 2024 review, co-written by the chair of the FAO consultation, concluded DIAAS is currently the most accurate routine score for single-source proteins. [3][1] The authors declared no commercial conflicts. [3]
- Processing. Processing does not always improve digestibility. [3]
- Health outcomes. Proper evidence not found. A Europe PMC title search on 2026-10-23 for DIAAS or its full name with randomized, trial, muscle or outcomes returned score-calculation studies, none described as testing long-term health outcomes by DIAAS. FAO describes PDCAAS as intended to assess how well dietary protein can match the demand for amino acids, which is an amino acid measure rather than a health result. [1]
Safety and who should ask
References
- FAO Food and Nutrition Paper 92: Dietary protein quality evaluation in human nutrition. Report of an FAO Expert Consultation, Auckland, 31 March to 2 April 2011 (FAO, Rome, 2013). Read 2026-10-23.
- U.S. Electronic Code of Federal Regulations, Title 21, section 101.9: Nutrition labeling of food (Food and Drug Administration), as displayed on eCFR. Read 2026-10-23.
- Moughan PJ, Lim WXJ. Digestible indispensable amino acid score (DIAAS): 10 years on. Frontiers in Nutrition 2024;11:1389719. Read 2026-10-23.
- NIDDK (U.S. National Institutes of Health): Eating and nutrition for chronic kidney disease, last reviewed January 2025. Read 2026-10-23.