Nutrition Diet: What is the preferred best method for determining the protein quality?

October 13, 2025 •

3 min read

According to the Food and Agriculture Organization (FAO), the scientific community now considers the Digestible Indispensable Amino Acid Score (DIAAS) to be the most accurate and preferred method for determining the protein quality. This modern metric offers a significant improvement over previous assessment techniques by more precisely measuring how the body digests and utilizes amino acids.

Quick Summary

This article explores the evolution of protein quality assessment, comparing older, less accurate methods with the modern DIAAS, which is based on ileal digestibility. The content details the specific advantages of DIAAS over the widely used PDCAAS method, which provides a more robust and comprehensive evaluation for determining protein quality.

Key Points

DIAAS is the Modern Standard: The Digestible Indispensable Amino Acid Score (DIAAS) is the most accurate and currently preferred method for determining protein quality, as recommended by the FAO.
Ileal vs. Fecal Digestibility: DIAAS uses ileal digestibility, measuring amino acid absorption at the end of the small intestine for greater accuracy, unlike PDCAAS which uses less precise fecal digestibility.
Uncapped Scores for Better Ranking: DIAAS scores are not capped at 100%, allowing for clearer differentiation and ranking of high-quality protein sources, a limitation of the older PDCAAS method.
Outdated Methods: Earlier methods like the Protein Efficiency Ratio (PER) and Biological Value (BV) are less relevant for human nutrition as they rely on animal growth or only partial measures of nitrogen retention.
Informs Nutritional Choices: A higher DIAAS score indicates a protein is more efficiently digested and utilized, helping consumers and food manufacturers choose and formulate products for optimal amino acid intake.
Impacts Public Health Policy: Accurate metrics like DIAAS are vital for regulations concerning protein content claims on food labels, ensuring scientific validity for consumers.

The evaluation of protein quality has evolved significantly over time as nutritional science has advanced. Early methods offered a less complete picture, while modern techniques, particularly DIAAS, provide greater accuracy by considering both the amino acid profile and its true digestibility in the human body. Understanding these methods is crucial for making informed dietary choices and for the food industry in accurately labeling products.

The Building Blocks of Protein Quality

Protein quality is defined by two primary factors:

Amino Acid Composition: A high-quality protein contains all nine essential amino acids (EAAs) in sufficient quantities. The body cannot synthesize these and must obtain them from the diet.
Digestibility and Bioavailability: This measures how effectively the body can break down and absorb protein for use in protein synthesis. Factors like food processing can affect this.

Proteins with a well-balanced EAA profile and high digestibility are considered higher quality, relevant for various diets, including plant-based ones.

Outdated Methods: Limitations of Early Assessments

Early methods relied on less precise measurements, often using animal models or overall nitrogen retention rather than specific amino acid utilization.

Protein Efficiency Ratio (PER)

PER measures weight gain in weanling rats fed test proteins. It is still a standard for infant formula in Canada. However, it has limitations as rat amino acid requirements differ from humans, and it assumes all weight gain is from protein.

Biological Value (BV)

BV assesses the proportion of absorbed protein nitrogen retained by the body, based on nitrogen balance studies. It doesn't account for digestibility and is difficult to measure accurately in humans.

The Prevailing Standard: Protein Digestibility Corrected Amino Acid Score (PDCAAS)

PDCAAS, adopted by FAO/WHO in 1993, combines amino acid requirements with fecal protein digestibility. It has limitations, including scores capped at 1.00 and the use of fecal digestibility which can overestimate true availability. It also uses a single digestibility value for the entire protein.

The Modern Gold Standard: Digestible Indispensable Amino Acid Score (DIAAS)

Recommended by the FAO in 2013, DIAAS is considered the most accurate method for protein quality. It calculates scores based on the true ileal digestibility of individual indispensable amino acids, providing a more accurate measure of what is available to the body. DIAAS scores are not capped, allowing for better ranking of high-quality proteins and uses updated amino acid reference patterns.

Comparison of Key Protein Quality Assessment Methods


Feature	PDCAAS	DIAAS	BV	PER
Digestibility Measurement	Fecal (total protein)	Ileal (individual amino acids)	None (only absorbed nitrogen)	None (based on weight gain)
Score Truncation	Truncated at 1.00	Not truncated	Varies, can be >100 with complementarity	Normalized to casein at 2.5
Primary Test Subject	Rat (for digestibility)	Pig or human (preferred)	Rat or human (inaccurate)	Weanling rat
Amino Acid Specificity	Based on single limiting amino acid after applying whole protein digestibility	Individual digestibility measured for each indispensable amino acid	Relies on the composition, but does not measure individual availability	Does not directly measure amino acids; inferred from growth
Primary Limitation	Capped score, overestimation of digestibility due to fecal measurement	Still limited data available for some foods, cost and ethical concerns with animal testing	Ignores digestibility and has experimental difficulties	Based on rat growth, not directly applicable to human needs

Implications of Using DIAAS for Nutritional Guidance

The adoption of DIAAS offers several benefits for dietary recommendations and food science. It provides a more accurate ranking of protein quality, enhances blending strategies by guiding food formulation, and can inform public health policy regarding protein content claims on food labels.

Conclusion

DIAAS is considered the most comprehensive and accurate approach for determining protein quality compared to older methods like PDCAAS, BV, and PER, by using true ileal digestibility of individual indispensable amino acids. Understanding and utilizing DIAAS is beneficial for consumers and food producers for optimal protein intake.

For more detailed information on DIAAS, refer to {Link: ncbi.nlm.nih.gov https://pmc.ncbi.nlm.nih.gov/articles/PMC11252030/}.

Frequently Asked Questions

The primary difference lies in how they measure protein digestibility. PDCAAS uses a less accurate fecal digestibility measure for the whole protein, while DIAAS uses more precise ileal digestibility for each individual indispensable amino acid.

DIAAS is more accurate because it uses true ileal digestibility, which measures the amino acids absorbed in the small intestine before they are potentially modified by gut bacteria. It also evaluates each amino acid individually and does not truncate high scores.

PER is limited because it uses a rat growth model, which may not translate accurately to human nutrition. It also only measures weight gain relative to protein intake, without accounting for maintenance needs or body composition changes.

Yes, unlike PDCAAS which is capped at 100%, DIAAS can exceed this value. A score greater than 100% indicates that the protein provides more than 100% of the required amino acids per gram, which is beneficial for complementing other, lower-quality proteins.

Food processing, especially intense heat, can damage or alter amino acids, potentially reducing their bioavailability. DIAAS takes into account the effects of processing, especially for vulnerable amino acids like lysine.

While recommended by the FAO, DIAAS has not been universally adopted for regulatory use. Some jurisdictions still rely on older methods like PDCAAS or PER, so it is important to check local regulations.

For a consumer, a high DIAAS score means the protein source is more efficiently utilized by the body. This is particularly useful for optimizing protein intake, especially for athletes or those with higher protein needs.

Yes, combining different protein sources can improve overall quality through complementarity, where one protein source provides an amino acid that is limiting in another. DIAAS is particularly effective at demonstrating this synergistic effect.

A limiting amino acid is the essential amino acid present in the lowest quantity relative to the body's requirements within a particular protein source. It is the factor that limits the body's ability to synthesize new protein.