What Is the Protein Digestibility-Corrected Amino Acid Score?
The Protein Digestibility-Corrected Amino Acid Score, or PDCAAS, evaluates protein quality based on amino acid profile and digestibility. It measures how well a protein can meet human essential amino acid needs after digestion. The score ranges from 0.0 to 1.0, indicating the protein's ability to provide essential amino acids. A score of 1.0 means the protein supplies 100% or more of required essential amino acids per unit after digestion. PDCAAS was the standard recommended by the FAO and WHO and adopted by the U.S. FDA.
The PDCAAS Calculation and Reference Pattern
PDCAAS calculation involves determining the amino acid score and correcting for protein digestibility.
- Amino Acid Score (AAS): Compares the limiting essential amino acid in a protein to a reference pattern. The limiting amino acid is the one in the lowest quantity relative to human needs. The reference pattern was based on preschool children's needs.
- True Fecal Digestibility (FTPD): Measures protein absorption, originally using a rat assay. The final PDCAAS is the AAS multiplied by the FTPD, capped at 1.0.
Advantages and Limitations of PDCAAS
PDCAAS was an improvement but had limitations that led to the development of a successor. {Link: PDCAAS – Knowledge and References taylorandfrancis.com} Some advantages included its simplicity, human-centric comparison, and use as a regulatory standard for food labels. Limitations included capping scores at 1.0, using fecal instead of ileal digestibility, not fully accounting for antinutritional factors, and assuming uniform amino acid digestibility.
The Shift to DIAAS
The FAO recommended the Digestible Indispensable Amino Acid Score (DIAAS) in 2011 as a more accurate method. DIAAS addresses PDCAAS limitations using true ileal amino acid digestibility, a more precise reference pattern, and eliminating score truncation.
Key differences between PDCAAS and DIAAS
| Feature | PDCAAS (Protein Digestibility-Corrected Amino Acid Score) | DIAAS (Digestible Indispensable Amino Acid Score) |
|---|---|---|
| Digestibility Method | Measures crude protein digestibility in the feces (typically using rats). | Measures individual amino acid digestibility at the end of the small intestine (ileum). |
| Maximum Score | Capped at 1.0, so all high-quality proteins receive the same score. | Not capped, allowing for better differentiation and comparison of high-quality proteins. |
| Reference Pattern | Historically based on the requirements of preschool children. | Uses updated reference patterns for different age groups (infants, children, and adults). |
| Accuracy | Prone to overestimating the quality of certain proteins, especially some plant-based sources. | Considered a more accurate reflection of protein quality and bioavailability for humans. |
Common PDCAAS Values
- Dairy Proteins (Casein, Whey): 1.0
- Eggs: 1.0
- Soy Protein Isolate: 1.0
- Beef: 0.92
- Pea Protein Concentrate: 0.89
- Black Beans: 0.75
- Rice: 0.50
- Wheat Gluten: 0.24
Why Lower Scores Don't Mean Useless Protein
A lower PDCAAS score doesn't mean a protein is useless. For example, wheat gluten is low in lysine. Combining it with a lysine-rich protein, like legumes, improves the overall protein quality of a meal. This concept, protein complementarity, is vital for dietary planning, especially for vegetarian and vegan diets. PDCAAS helped establish the science behind this practice. More information on protein quality evaluation is available from organizations like the FAO.
Conclusion: The Legacy of PDCAAS
PDCAAS was a foundational tool for evaluating protein quality based on human needs. Despite limitations like score truncation and fecal digestibility, leading to its replacement by DIAAS in 2011, its legacy is significant. PDCAAS educated nutrition professionals and standardized food labeling. Understanding PDCAAS is key to appreciating the evolution of protein quality assessment. The move to DIAAS represents a more precise evaluation benefiting consumers and manufacturers. For more information on dietary protein quality evaluation, consult resources from organizations like the Food and Agriculture Organization (FAO). {Link: PDCAAS – Knowledge and References taylorandfrancis.com}
