What Defines Protein Quality?
To understand protein quality, one must consider three primary factors: the amino acid composition, the protein's digestibility, and its bioavailability. Proteins are made up of amino acids, and the human body requires 9 essential amino acids (EAAs) that it cannot produce on its own. A "complete" protein is one that contains all 9 EAAs in sufficient quantities. Digestibility measures how much of the protein is broken down and absorbed, while bioavailability refers to how well the absorbed amino acids are utilized for protein synthesis.
Animal proteins are generally considered complete and highly bioavailable. Plant proteins often lack sufficient amounts of one or more essential amino acids, but combining different plant-based foods throughout the day can provide a complete amino acid profile. Food processing methods can also impact protein quality.
The Evolution of Protein Scoring: From PDCAAS to DIAAS
For many years, the Protein Digestibility Corrected Amino Acid Score (PDCAAS) was the standard for measuring protein quality. Developed by the Food and Agriculture Organization (FAO) and World Health Organization (WHO) in 1993, PDCAAS compares a protein's amino acid profile to the needs of a preschool-aged child and corrects for fecal digestibility. However, this method has limitations that led to the development of a more accurate metric.
Limitations of PDCAAS
- Truncated Score: PDCAAS scores are capped at 1.0, which means it cannot differentiate between proteins of very high quality.
- Inaccurate Digestibility: By using fecal digestibility, PDCAAS may overestimate amino acid absorption due to the activity of gut bacteria.
Introducing DIAAS: The Gold Standard
In 2013, the FAO recommended replacing PDCAAS with the Digestible Indispensable Amino Acid Score (DIAAS). DIAAS offers a more accurate and detailed assessment of protein quality.
How DIAAS Is Calculated
DIAAS improves upon PDCAAS in several key areas:
- Ileal Digestibility: DIAAS measures digestibility at the end of the small intestine, providing a more accurate reflection of absorbed amino acids available to the body.
- Untruncated Score: DIAAS scores are not capped, allowing for better differentiation among high-quality proteins.
- Age-Specific Reference Patterns: DIAAS can utilize age-specific amino acid requirements for different populations.
Factors Influencing Protein Quality
Beyond amino acid content, other factors influence how well the body utilizes protein.
Bioavailability
Bioavailability is the extent to which absorbed amino acids are available for protein synthesis. Antinutritional factors in some foods can reduce bioavailability, but processing methods like heating can improve it.
Protein Source and Processing
Animal proteins generally have a more favorable amino acid balance and higher digestibility compared to plant proteins. However, processing can impact quality; isolates may be more digestible due to fewer antinutritional factors, while overheating can reduce the availability of certain amino acids.
Dietary Complementation
Combining different plant protein sources throughout the day, such as grains and legumes, ensures a complete intake of essential amino acids.
Comparison of Protein Scoring Systems
| Feature | PDCAAS (Protein Digestibility Corrected Amino Acid Score) | DIAAS (Digestible Indispensable Amino Acid Score) |
|---|---|---|
| Approval | Adopted by FAO/WHO in 1993; still used in some regulations. | Recommended by FAO in 2013 to replace PDCAAS. |
| Score Range | Truncated at 1.0, meaning scores above 1.0 are rounded down. | Untruncated, allowing for scores >1.0 for very high-quality proteins. |
| Digestibility | Based on fecal digestibility, which can be inaccurate due to gut bacterial activity. | Based on ileal digestibility, measuring absorption at the end of the small intestine. |
| Reference Pattern | Uses a reference pattern based on the needs of 2–5 year-old children. | Can use age-specific reference patterns for different populations. |
| Application | Less effective for comparing high-quality proteins or for mixed-protein diets. | More accurate for comparing different protein sources and for single-source diets. |
Practical Application: How to Use This Information
Understanding protein scoring methods like DIAAS can be beneficial for making informed dietary choices. For most people with a varied diet, consuming a mix of protein sources ensures adequate essential amino acid intake. For those with specific needs, such as athletes or older adults, or those following plant-based diets, being aware of protein quality can help optimize dietary choices or supplement selection. For example, protein supplements with higher DIAAS scores may indicate superior quality due to the untruncated scoring and accurate digestibility measurement. {Link: The FAO https://www.fao.org/ag/humannutrition/36262-092570d588a44b36c478641925b44d930.pdf} report recommending DIAAS provides further detailed insight for professionals and consumers alike.
Conclusion
The Digestible Indispensable Amino Acid Score (DIAAS) is the current gold standard for determining protein quality, offering a more accurate and detailed assessment than its predecessor, PDCAAS. By measuring ileal digestibility and providing untruncated scores, DIAAS helps consumers and professionals make more informed decisions about dietary protein sources and supplements. A varied diet of high-quality protein remains key for meeting nutritional needs.
