What is Protein Quality?
To understand what is the true protein digestibility score, you must first understand the concept of protein quality. Protein is composed of amino acids, nine of which are considered indispensable (or essential) because the human body cannot produce them in sufficient quantities and must obtain them from food. The quality of a protein source is determined by its amino acid profile—specifically, whether it contains all nine indispensable amino acids—and its digestibility. A "complete" or high-quality protein provides an optimal balance of these building blocks, while an "incomplete" or lower-quality protein is deficient in one or more. Measuring this quality accurately is crucial for making informed dietary choices and for the food industry in formulating nutritional products.
The Limitations of the Old Standard (PDCAAS)
For many years, the Protein Digestibility-Corrected Amino Acid Score (PDCAAS) was the standard for measuring protein quality. The PDCAAS method had several significant flaws that led to inaccurate and misleading results.
The Rise of DIAAS: The True Digestibility Score
To overcome the shortcomings of PDCAAS, the FAO introduced the Digestible Indispensable Amino Acid Score, or DIAAS, in 2013 as the new standard. DIAAS provides a more accurate and detailed assessment of protein quality with key improvements:
- Ileal Digestibility: Measures digestibility at the end of the small intestine for better accuracy of absorbed amino acids.
- Uncapped Scores: Allows scores above 100%, providing a more nuanced ranking of protein quality.
- Individual Amino Acid Scoring: Calculates digestibility for each indispensable amino acid to identify the limiting amino acid.
- Age-Specific Requirements: Considers different amino acid needs for various age groups.
A Comparison of Protein Digestibility Scores
To better illustrate the differences, let's compare how various proteins are rated under both the old PDCAAS and the more modern DIAAS system. This comparison reveals how DIAAS provides a more accurate representation of protein quality and nutritional value.
| Protein Source | PDCAAS Score | DIAAS Score (0.5-3 yo) | Key Difference | Limiting Amino Acid (DIAAS) |
|---|---|---|---|---|
| Whey Protein Isolate | 1.00 | 1.09 | DIAAS shows superior quality beyond the PDCAAS cap | Valine |
| Soy Protein Isolate | 0.98 | 0.898 | DIAAS reveals lower digestibility than PDCAAS suggests | Methionine + Cysteine |
| Milk Protein Concentrate | 1.00 | 1.18 | DIAAS shows higher quality, overcoming PDCAAS capping | Methionine + Cysteine |
| Pea Protein Concentrate | 0.893 | 0.822 | DIAAS provides a more realistic digestibility value | Methionine + Cysteine |
| Beef | 0.92 | 1.116 | DIAAS highlights a higher quality protein once uncapped | None (exceeds 100) |
Implications for a Nutrition Diet
Understanding DIAAS provides a better tool for meal planning and making informed choices about protein sources. It's particularly useful for those on plant-based diets, emphasizing the importance of combining complementary proteins like legumes and grains to achieve a complete amino acid profile and a higher DIAAS. For individuals like athletes, selecting foods with a high DIAAS ensures efficient nutrient utilization for muscle support and overall health.
Conclusion
The shift from PDCAAS to DIAAS is a significant improvement in assessing protein quality. By measuring individual amino acid digestibility in the small intestine and providing uncapped scores, DIAAS offers a more accurate and relevant picture of a protein's nutritional value. This helps consumers make better dietary decisions, supports accurate food labeling, and improves nutritional intake and health.
Why Understanding DIAAS Matters for Protein Intake
- Higher Quality, Better Outcomes: High DIAAS proteins provide a more balanced and digestible supply of essential amino acids, supporting muscle protein synthesis and health.
- Personalized Nutrition: DIAAS considers age-specific needs for better-tailored diets.
- Enhanced Plant-Based Diet Planning: DIAAS guides those on plant-based diets in combining proteins for complete amino acid profiles.
- Accurate Labeling: Uncapped scores and ileal digestibility offer more transparent information for consumers and manufacturers.
- Informed Supplement Choice: DIAAS provides a clearer indication of a protein supplement's effectiveness.
- Optimized Nutrient Utilization: DIAAS measures true absorption, ensuring consumed protein is used by the body.
- More Meaningful Comparison: DIAAS allows for better comparison of high-quality proteins by removing the capping limitation.
- Addressing Anti-Nutritional Factors: DIAAS considers factors affecting digestibility in plant proteins for a realistic assessment.
- Improved Health and Performance: High DIAAS protein is crucial for muscle repair, growth, and performance.
