PDCAAS vs. DIAAS: Protein Digestibility Scores for Labeling Compliance

PDCAAS and DIAAS are the primary methods used by the Food and Agriculture Organization and the World Health Organization for protein quality evaluation. While older methods, such as the protein efficiency ratio (PER) and biological value, focused on animal growth, modern methods analyze amino acid composition and human amino acid requirements to determine how well a protein supports protein synthesis and overall human nutrition.

This article lists the protein digestibility scores for common foods for food manufacturers and touches on the novel DIAAS method for protein quality scores.

If you’re stuck on how to determine the correct protein quality for your food labels, get in touch with one of our nutritionists so they can guide you through the process with expert consultation. 

What is the purpose of PDCAAs (Protein Digestibility-Corrected Amino Acid Score)

Food manufacturers rely on the The Protein Digestibility-Corrected Amino Acid Score (PDCAAS), the official FDA standard, to evaluate protein quality. 

This score measures how easily the body digests and absorbs protein, directly influencing product formulation and the protein content claims made on packaging. 

What is the purpose of DIAAs (Digestible Indispensable Amino Acid Score)?

The digestible indispensable amino acid score (DIAAS) is a modern approach to measuring the protein quality of foods based on how well individual amino acids are actually digested and absorbed by the body.

DIAAS uses true ileal digestibility, measuring amino acid digestibility at the end of the small intestine, rather than relying on fecal digestibility or true fecal nitrogen digestibility. This avoids distortions caused by gut bacteria and endogenous amino acid losses, which often confound true fecal nitrogen digestibility measurements. By focusing on true ileal digestibility, DIAAS accounts for anti-nutritional factors (like phytates in plant proteins) that may inhibit digestion in the small intestine, providing a superior measure of amino acid availability compared to fecal digestibility.

Unlike PDCAAS, DIAAS is not capped at 1.0, allowing clear differentiation between high-quality proteins. By assessing digestibility at the amino acid level—typically determined through laboratory analysis such as acid hydrolysis—DIAAS enables more precise comparisons between animal proteins, plant proteins, and blended protein sources.

When PDCAAS Is Legally Required as per the FDA

PDCAAS is the official regulatory standard for determining protein quality on nutrition labels in both the United States and Canada. It is required whenever a product makes a protein-related nutrition claim.

Manufacturers are legally required to apply PDCAAS when:

1. Making a protein content claim: “Good source of protein”, “High protein”, “Excellent source of protein”, “Added protein”, or any marketing claim implying protein quality.
2. Displaying the % Daily Value for Protein: The %DV on the Nutrition Facts label must be calculated as: (Protein grams per serving × PDCAAS) ÷ Daily Reference Value
3. When protein contributes to a nutrient content claim or comparison: Examples include “More protein than…”, “Reduced protein…”, “Protein-enriched…”
4. For foods intended for children ≥ 1 year: PDCAAS uses the preschool-age child amino acid reference pattern, mandated by FDA.
   

Food Manufacturers don’t need to worry about using PDCAAS under the following conditions:

1. If no protein claims are made
2. If the label shows only grams of protein (no %DV)
3. If the food is marketed without protein marketing emphasis

Under FDA regulations, protein claims (such as “good” or “excellent”) cannot be legally made unless a PDCAAS calculation has been carried out. Failing to do so could result in costly recalls which will affect brand reputation. 

PDCAAS Chart

Below is a PDCAAS chart that lists the protein sources, their digestibility values, and final PDCAAS score for common food items.

True protein digestibility (TD) measures the proportion of ingested protein that is absorbed by the body, accounting for metabolic nitrogen in fecal matter, whereas PDCAAS is the final, corrected value to be used to generate a compliant nutrition label. It’s important to remember that a PDCAAS value is a benchmark for making protein claims on food labels such as “Good protein source,” “Excellent protein source” or “Extra Protein.

It is also important for manufacturers to note that processing affects quality; for example, a highly purified whey protein isolate or rice protein concentrate may yield different true amino acid digestibility scores than whole foods. The table below compares animal proteins (which generally provide a complete standard amino acid profile) against plant proteins, which may have a limiting amino acid. 

The information in this table is particularly useful for food manufacturers and food service specialists who are keen on a correct protein quality evaluation to show on their food labels.

PDCAAS Calculation

Calculating the Protein Digestibility-Corrected Amino Acid Score (PDCAAS) is often seen as an overwhelming task because it demands several complex, time-consuming steps. 

It often starts with an expensive external lab analysis to accurately determine the precise amounts of all nine essential amino acids in your product. Once that is done, it must then compare their ingredient ratios against the official FDA reference pattern – for preschool-age children – to identify the single limiting amino acid and determine the product’s overall protein quality (often sulfur amino acids in legumes or lysine in grains). 

Finally, this determined amino acid score must be corrected by sourcing the appropriate True Protein Digestibility (TPD) factor for the ingredient. Keep in mind that TPD changes significantly based on processing methods, before arriving at the final, capped score required for your food label claims.

The Next Standard – What is DIAAS?

Digestible Indispensable Amino Acid Score (DIAAS) is a method, supported by the Food and Agriculture Organization (FAO),  that introduces the use of ileal amino acid digestibility coefficients and untruncated protein scores. There were concerns with the PDCAAS method as it led to overestimating protein quality. DIAAS measures true ileal digestibility (at the small intestine) for each individual indispensable amino acid, to avoid the inaccurate fecal measurements and microbial interference of PDCAAS. Also, the DIAAS score is not capped at 1.0, allowing for accurate differentiation and ranking of very high-quality proteins that the PDCAAS method system simply grouped together.

Below is a table with DIAAS values for common food ingredients:

DIAAS values are based on true ileal digestibility rather than fecal digestibility, giving a clearer picture of individual amino acids absorbed in the small intestine.

Step-by-step DIAAS Calculation

Follow the 4 steps below to carry out an accurate DIAAS calculation and get an accurate protein quality evaluation. 

1. Determine the amount of each indispensable amino acid (IAA) in 1 gram of the test protein using laboratory methods like acid hydrolysis. This is based on the protein’s amino acid content and its standardized ileal digestibility (SID). Unlike PDCAAS, which truncates values, DIAAS allows you to highlight high-quality proteins that exceed the reference protein requirements.
   • The formula is: (mg of specific IAA in 1 g of test protein) x (SID of that IAA).
2. Determine the amount of each IAA in 1 gram of the reference protein. These values are based on established reference patterns for a specific age group (e.g., infants, children, adults).
3. Calculate the “digestible indispensable amino acid reference ratio” for each IAA. Divide the amount of the digestible IAA from the test protein by the amount of the same IAA in the reference protein.
   • The formula is: (mg of digestible IAA in 1 g of test protein) / (mg of the same IAA in 1 g of reference protein).
4. Calculate the final DIAAS score. Multiply the lowest “digestible indispensable amino acid reference ratio” calculated in the previous step by 100 to get a percentage.

Final Thoughts: How to Calculate PDCAAS Easily

While DIAAS is the scientific standard and is being increasingly used in academic research, PDCAAS still remains the regulatory standard especially in the U.S and Canada. 

Therefore, to ensure your food labels are up-to-date with FDA and CFIA food labeling regulations, we’ve integrated PDCAAS into our tool – making it easier for protein quality to be determined. You can now easily get an accurate protein quality score by either using the PDCAAS value from the table in this article, or if you’d prefer to carry out your own calculations you can use the Food Label Maker tool to get the required values for the PDCAAS formula.

To calculate your PDCAAS score, simply input your protein digestibility value (from the table in this article), use the tool to instantly generate a full amino acid profile (called the Amino Acid Report) and automatically identify the limiter.

Once you add your PDCAAS score to your recipe, on the foodlabelmaker.com dashboard, your protein per serving will be automatically multiplied by the PDCAAS value giving you a final, compliant, protein quality score.

If you’d like to learn more about how Food Label Maker can help you, book a demo with one of nutrition experts. 

Frequently Asked Questions

Should I use DIAAS or PDCAAS to calculate protein quality?

You can use both, however, PDCAAS is still the most widely used method in the FDA and CFIA regulatory standards.

While the Digestible Indispensable Amino Acid Score (DIAAS) is considered the scientifically superior and most accurate method, the Protein Digestibility Corrected Amino Acid Score (PDCAAS) is still the most widely used method in regulatory frameworks globally for food labeling and protein content claims. Even though DIAAS was officially recommended by the FAO to replace the old standard, it still requires full adoption by government regulatory bodies. This is because they require more time to generate standardized DIAAS data across all foods and update existing food policy.

If you need help using the PDCAAS method and you’re not sure how to determine the limiting amino acid of your food item, book a demo with one of our nutrition experts so they can walk you through one of our useful features – the Amino Acids Pattern Report. 

What’s the difference between true protein digestibility and PDCAAS?

The terms true protein digestibility and PDCAAS (Protein Digestibility Corrected Amino Acid Score) are related but represent different concepts in protein quality assessment. 

Older measures such as biological value and protein efficiency ratio are no longer recommended for modern protein quality evaluation.

Protein Digestibility is the adjustment factor that tells you what percentage of the protein you eat is actually absorbed by the body. The PDCAAS (Protein Digestibility Corrected Amino Acid Score) is the final quality score that uses this adjustment factor to downgrade a protein’s initial quality based on how poorly it is digested and absorbed.

Essentially:

• Amino Acid Score = How good the protein is on paper (its ideal amino acid composition).
• Protein Digestibility = How much of that protein actually makes it into your system.
• PDCAAS = Amino Acid Score x Protein Digestibility (The final, real-world score).

To learn more about protein quality and how to make accurate protein content claims, book a demo with one of our nutrition experts. 

How do I use PDCAAS in Multi-Ingredient Formulations?

In the case of having recipes made of different ingredients, or dietary supplements (e.g., blending milk proteins with pea protein), you’ll end up having multiple ingredients that contribute to the protein amount per serving, and you cannot simply average the scores. 

You must calculate the protein quality of the blend. If one ingredient is low in a specific amino acid, another ingredient rich in that same amino acid can compensate. This is known as protein complementation, and it improves the overall amino acid profile and biological value of the final product.

To do so:

1. Calculate the Combined Amino Acid Score (AAS):

Find the limiting amino acid in the entire protein mixture. Sum the essential amino acids (EAAs) from all ingredients. Compare this total EAA profile (per gram of total protein) against the human reference pattern. The lowest ratio found is the AAS.

2. Calculate the Weighted Average Protein Digestibility (PD):

Find the overall digestibility of the total protein. Determine the percentage of total protein contributed by each ingredient. Multiply that percentage by the ingredient’s known digestibility factor. Sum these weighted values to get the Weighted Average PD.

3. Determine the Final PDCAAS:

Formula: PDCAAS = AAS x Weighted Average PD

Rule: The final score is capped at 1.0 (100%) regardless of the calculated value.

Both the amino acid pattern and the overall protein digestibility change once proteins are blended, which means the final PDCAAS must be calculated for the entire formulation, not for each ingredient in isolation.

If you need help calculating the PDCAAS value for your recipe, hire one of our experts with experience in labeling regulations across the FDA, CFIA and more global markets. 

Important Note on Values: PDCAAS scores, Protein Digestibility coefficients, and DIAAS values are compiled from various scientific and regulatory publications and are provided for conceptual and educational purposes. 

Due to differences in raw material sourcing, ingredient isolation techniques, and the limitations of the in vivo testing method, you may encounter differing values. It is essential practice to fully document the authoritative source for any value used in commercial nutrition labeling.

This article was updated on 2nd December 2025. Please be advised that regulatory standards and scientific understanding of protein quality, particularly concerning the transition between PDCAAS and DIAAS, are continually evolving. 

Sources

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC7760812/#:~:text=at%20least%200.75.-,Table%202.,-Protein%20quality%20of 
2. https://www.foodrisk.org/resources/sendFile/88 
3. https://pubmed.ncbi.nlm.nih.gov/32932087/ 
4. https://openknowledge.fao.org/server/api/core/bitstreams/ef6594d6-1fff-45a5-93e3-c12ab7a0e332/content 
5. https://www.jssm.org/vol3/n3/2/v3n3-2pdf.pdf 
6. https://www.researchgate.net/publication/232737392_Protein_quality_evaluation_twenty_years…
7. https://www.sciencedirect.com/topics/food-science/digestible-protein 
8. https://www.fao.org/ag/humannutrition/35978-02317b979a686a57aa4593304ffc17f06.pdf