What Does a PDCAAS of 1 Mean? Decoding High-Quality Protein

December 6, 2025 •

3 min read

According to regulatory bodies like the FDA and WHO, the Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a standard measure for protein quality. A PDCAAS of 1 means that, after digestion, the protein provides 100% or more of all the indispensable amino acids required per unit of protein. This top score indicates the protein is complete and highly bioavailable for the human body.

Quick Summary

A PDCAAS of 1 indicates the highest possible protein quality, signifying a complete amino acid profile and high digestibility. This score is used in nutritional labeling to represent a protein source that provides all essential amino acids in sufficient amounts for human needs. A PDCAAS of 1 reflects superior nutritional value.

Key Points

Highest Protein Quality: A PDCAAS of 1 indicates the highest possible protein quality, representing a complete and highly digestible protein source.
Complete Amino Acid Profile: A score of 1 means the protein contains all nine essential amino acids in sufficient amounts to meet human needs.
High Bioavailability: This top score confirms that the body can effectively digest and absorb the protein's amino acids.
Found in Top Sources: Proteins like whey, casein, eggs, and isolated soy protein are known to have a PDCAAS of 1.
Standard for Labeling: The PDCAAS is a widely used metric by regulatory bodies like the FDA for protein content labeling.
Capped Score: Any protein with a raw score over 1.0 is truncated to 1.0, which can limit comparison between superior proteins.
Different from DIAAS: The newer DIAAS method avoids truncation and uses a more accurate ileal digestibility measure, providing more differentiation.

Demystifying the Protein Digestibility Corrected Amino Acid Score (PDCAAS)

Evaluating protein quality goes beyond just the quantity of protein; it's also about the amino acid composition and how well the body can use it. The Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a key metric used by the food industry and regulators like the FDA to assess protein quality. A PDCAAS of 1 represents the highest possible score, indicating a protein source of superior nutritional value.

The Anatomy of a PDCAAS Score

The PDCAAS is calculated based on two main factors: the amino acid score and protein digestibility. The amino acid score compares the essential amino acid profile of a food to a reference pattern, typically based on the needs of young children. The limiting amino acid, the essential amino acid present in the lowest amount relative to the reference pattern, determines the amino acid score. This score is then multiplied by the protein digestibility, which measures how much of the protein is absorbed by the body.

While a protein's raw score might exceed 1.0, the PDCAAS is capped at 1.0. This means that a protein with a calculated score higher than 1.0 is still reported as 1.0. This capping has led to criticisms, and newer methods like DIAAS have been developed as alternatives.

What a PDCAAS of 1 Means in Practice

A PDCAAS of 1 signifies that the protein, after digestion, provides all the essential amino acids needed by humans in sufficient quantities. This means less of this protein is required to meet essential amino acid needs compared to proteins with lower scores. This makes proteins with a PDCAAS of 1 highly efficient and valuable for various dietary goals.

Foods with a PDCAAS of 1

Several protein sources achieve a PDCAAS of 1, being considered 'complete proteins' because they provide all nine essential amino acids.

Common PDCAAS 1 Protein Sources

Milk proteins (whey and casein)
Eggs and egg whites
Isolated soy protein
Some fermented plant proteins

Comparison of Protein Scoring Methods: PDCAAS vs. DIAAS

The Digestible Indispensable Amino Acid Score (DIAAS) is a newer method recommended by the FAO. It addresses some limitations of PDCAAS, particularly in measuring digestibility more accurately and avoiding score truncation.


Feature	PDCAAS	DIAAS
Digestibility Measurement	Fecal digestibility, potentially overestimating absorption.	Ileal digestibility, offering a more precise measure of absorption in the small intestine.
Score Truncation	Capped at 1.0, limiting differentiation of high-quality proteins.	Not truncated, allowing for better comparison among superior proteins.
Reference Pattern	Based on needs of preschool children.	Uses updated reference patterns for different age groups.

Despite the limitations and the introduction of DIAAS, PDCAAS remains a widely used method for protein labeling, particularly in the US.

Conclusion

A PDCAAS of 1 indicates a protein source that is complete in its essential amino acid profile and highly digestible, representing a high standard in protein quality. While newer methods like DIAAS offer more refined assessments, the PDCAAS provides a fundamental understanding of a protein's nutritional value. Recognizing what a PDCAAS of 1 means can help consumers choose food sources that efficiently contribute to their daily protein and essential amino acid needs.

Frequently Asked Questions

A PDCAAS of 1 indicates a protein that is both complete in its essential amino acid profile and highly digestible. A score below 1 means the protein is either missing or has an insufficient amount of one or more essential amino acids, or is not as easily digested.

Not necessarily in all contexts. While a score of 1 technically signifies a higher quality protein, the capping of the score at 1.0 means proteins that might have a higher underlying quality are rated identically. A protein with a score of 0.95 is still considered a very high-quality protein source.

Foods with a PDCAAS of 1 include animal-based proteins such as eggs, whey protein, and casein (milk protein), and plant-based proteins like isolated soy protein. Fermented plant proteins can also achieve this score.

A PDCAAS of 1 is a strong indicator of high-quality protein, but it is not the only factor to consider. Other nutritional aspects of the food, such as fat, carbohydrate, and vitamin content, are also important. Furthermore, a varied diet with a combination of different protein sources can provide a balanced amino acid intake.

The key difference is that DIAAS (Digestible Indispensable Amino Acid Score) uses ileal digestibility, which is more accurate than PDCAAS's fecal digestibility measurement. Additionally, DIAAS does not cap scores at 1.0, allowing for a better differentiation between high-quality protein sources.

Most plant-based proteins have lower PDCAAS scores than animal proteins. However, by combining different plant protein sources, vegetarians and vegans can easily achieve a complete amino acid profile throughout the day. For example, combining legumes (low in methionine) with grains (low in lysine) creates a complementary protein source.

Protein digestibility is crucial because it accounts for how much of the protein's amino acids are actually absorbed and utilized by the body. Without this correction, a protein's quality could be overstated.