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PDCAAS to DIAAS: A new way to look at protein quality

PDCAAS to DIAAS: A new way to look at protein quality.

Proteins are essential nutrients found in the human body and are the major structural component of all cells, including muscle, body organs, hair, and skin health.  Proteins from different sources have varying levels of nutritional value (learn more).  Due to the important role proteins play in our nutrition, it’s vital that consumers and brands have a reliable, standard measure to determine protein quality.

Protein quality describes both the content of amino acids in a dietary protein source and their bioavailability. There are many different ways to estimate the protein quality of a food.  Some methods focus on protein to support optimal growth, some on amino acid balance, others on the extent of digestion and absorption of protein, or indispensable amino acids relative to amino acid requirements.

The Food and Agricultural Organization of the United Nations/World Health Organizations (FAO/WHO) and the US FDA first proposed a protein quality evaluation method in 1991, the Protein Digestibility-Corrected Amino Acid Score (PDCAAS), and they made PDCAAS the official standard in 1993. But in 2013, FAO proposed shifting preference to a new evaluation method, the Digestible Indispensable Amino Acid Score (DIAAS).

The DIAAS standard won’t be implemented until a more complete catalog of scores has been tested and verified. FAO hopes for the official adoption of DIAAS, as a universal standard, sometime in the next 5 to 10 years.


What is the PDCAAS method?

PDCAAS (Protein Digestibility Corrected Amino Acid Score) evaluates a food’s protein quality.  It compares amino acid composition to what our bodies require. PDCAAS compares the amount of the essential amino acids in the food to a scoring pattern based on the essential amino acid requirements of a 2 to a 5-year old child to determine its most limiting amino acid (amino acid score).  Samples are taken at the end of the digestive cycle, from mouse feces.

The highest PDCAAS value that any protein can achieve is 1.0, indicating that the protein will provide 100% (or more) of all the amino acids required in the diet. Generally, casein, whey, soy, and egg are considered good quality proteins and have PDCAAS scores of 1.0, while those of tree nuts are a bit under 0.50 and wheat gluten even lower. The graph below compares some of the common protein sources.





What is the DIAAS method?

DIAAS is the ratio of the digestible amino acid content in the food (mg/g of protein) to the same amino acid in a reference pattern taken from age-specific amino acid requirements. The lowest value across amino acids is multiplied by 100 to convert the ratio to a percentage. This percentage represents the DIAAS of the food. Samples are taken from the ilium and are collected from a pig.  Pigs have more biological similarities to humans than rats.

Along with the new testing and score method, DIAAS will also impact protein claims on quality. Quality will be dictated by where the tested protein’s DIAAS score falls within the scale. Specific brackets are recommended below:

  • No protein quality claim – Score of <75%
  • Good protein quality – Score ranging from 75% to 99%
  • Excellent or High protein quality – Score of 100% or more


Why is DIAAS superior to PDCAAS?

There are many reasons why a shift from DIAAS to PDCAAS has been proposed. We’ll focus on two of said reasons, superior score method, and more accurate sampling method.

One criticism of PDCAAS is that the maximum achievable score is 1.0.  Proteins of higher quality are not identified or highlighted. Some proteins would score beyond the digestability scoring pattern range. The DIAAS method does not truncate the scores, allowing for a more accurate ranking of quality. For example, Whey Protein Isolate (WPI) has a PDCAAS of 1 and Soy Protein Isolate (SPI) has a PDCAAS of 0.98. WPI’s DIAAS score is 1.09 while SPI’s DIAAS score drops to 0.90. This is a more clear distinction of quality and gives consumers better information for more informed decisions.

Amino acids are less likely to be absorbed after passing through the ileum. DIAAS samples come from the ilium, while PDCAAS samples come from feces. If there are no amino acids in the feces sample, the PDCAAS method assumes digestion. But the DIAAS sample from the ilium is a more accurate representation of amino acid digestion and absorption.

Below you can find a chart that compares PDCAAS and DIAAS scores for some common protein sources. PDCAAS doesn’t have the range or differentiation between some sources depicted by DIAAS. That difference is why the nutrition community is pushing for this official change.



What does this change mean for you?

The database is not yet complete, but you should start reviewing your protein sources and how they fall into the DIAAS model. This information will be used in consumer decision making and should be considered when formulating new products.

It is very critical to have accurate but practical methods available to industry, clinicians, public health practitioners, policymakers, and food aid agencies to ensure we make the best food and diet choices for a range of consumers to meet their optimal nutritional needs.  Consumers should also be well educated on how important high-quality protein is, to pick the best food product from collective choices in the market. The food industry should do its part to educate consumers on this standard change and empower their nutrition choices.


How can Agropur help?

We’re protein people and are happy to help you navigate sourcing and formulating questions. As the number one whey protein manufacturer in North America, we are dedicated to supplying high quality, competitively priced whey protein fractions and dairy ingredients. As formulators and distributors, we can offer insight into alternative proteins like pea or rice, and source ingredients for your specific project or formulation.



  • Consultation, FAO Expert. “Dietary protein quality evaluation in human nutrition.” FAO Food Nutr. Pap 92 (2011): 1-66.
  • Food and Agriculture Organization of the United Nations. Dietary Protein Quality Evaluation in Human Nutrition: Paper 92. Rome, Italy: Food and Agriculture Organization of the United Nations; 2013.
  • Mathai, John K., Yanhong Liu, and Hans H. Stein. “Values for digestible indispensable amino acid scores (DIAAS) for some dairy and plant proteins may better describe protein quality than values calculated using the concept for protein digestibility-corrected amino acid scores (PDCAAS).” British Journal of Nutrition 117.4 (2017): 490-499.
  • Rutherfurd, Shane M., et al. “Protein digestibility-corrected amino acid scores and digestible indispensable amino acid scores differentially describe protein quality in growing male rats.” The Journal of Nutrition 145.2 (2014): 372-379.
  • Leser, S. “The 2013 FAO report on dietary protein quality evaluation in human nutrition: recommendations and implications.” Nutrition Bulletin 38.4 (2013): 421-428.
  • Marinangeli, Christopher PF, and James D. House. “Potential impact of the digestible indispensable amino acid score as a measure of protein quality on dietary regulations and health.” Nutrition reviews 75.8 (2017): 658-667.