How will the World Measure Protein Quality?

Originally Published: November 10, 2014
Last Updated: March 4, 2021
Lysine is one of nine essential amino acids not made by the body, and essential amino acids must be added to foods or beverages to make a complete protein.

October 31, 2014 -In a world where the population is growing by leaps and bounds, not only food, but the quality of that food, will become increasingly important. High- quality protein is essential for growth and maintaining a healthy body. In addition, it is imperative that decision-makers have a tool to properly assess protein quality, but, how will the world measure protein quality? And, why measure protein quality? It’s imperative so they can make good decisions when it comes to creating policy, establishing regulations and ensuring the public health.

In 1989, the Food and Agricultural Organization of the United Nations (FAO) proposed that the PDCAAS be utilized as a tool for evaluating protein quality, said Joyce Boye, Ph.D., Agriculture & Agri-Food Canada. This is determined by multiplying the limiting amino acid score by protein digestibility. The limiting amino acid score is defined as “The ratio of first limiting amino acid in a gram of target food to that in a reference protein or requirement.”

PDCAAS has been utilized since that time for determining protein quality. There are a number of concerns with regards to this tool, however. These include the need to establish specific analytical methods for measuring amino acids in different foods; under- or overestimating the actual bioavailability of foods, especially when it came to
addressing potential amino acid availability; and a failure to account for the difference between protein  digestibility and amino acid digestibility. To address these concerns and review other tools for evaluating protein quality, the FAO established an Expert Consultation group.

This group issued its recommendations in 2013. Among these recommendations were:
• Dietary amino acids should be treated as individual nutrients;
• Digestible amino acids should be used to calculate protein digestibility as opposed to digestible protein;
• When evaluating lysine, available or reactive lysine should be used;
• Ileal amino acid digestibility should be used; and
• Determinations for each indispensable amino acid should preferably be determined using humans. If this is not possible, pigs or rats should be used.

Different scoring patterns were also included in these recommendations. The recommendations included those for infants, young and older children, plus considerations for regulatory applications.

The Expert Consultation group recommended that the Digestible Indispensable Amino Acid Score, or DIAAS, be adopted to replace PDCAAS. Percent DIAAS may be defined as follows. DIAAS % = 100 x [(mg of digestible dietary IAA in 1g of the dietary protein)/(mg of the same dietary IAA in 1g of the reference protein)]. The values are calculated for each indispensable amino acid (IAA) and the lowest value is designated as the DIAAS.

There are, however, challenges that must be addressed with DIAAS. One of these is the method to determine true ileal digestibility and the current dearth of data on this all-important factor. In the interim, options include utilizing protein digestibility as an equivalent for amino acid digestibility; and if true ileal protein digestibility values are unavailable, utilizing true fecal protein digestibility as a substitute; and using protein digestibility to calculate digestible individual amino acids.

There are many challenges that must be met to enhance the overall food supply and, specifically, to enhance overall protein quality. Boye concluded by listing suggestions to help move forward in reaching these goals. The suggestions were that more data is needed on the true ileal amino acid digestibility of human foods (i.e., using human and animal models) and the need for inter-species (human, pig, rat) true ileal amino acid digestibility comparisons. Also, there is a need for data on the impact of processing, anti-nutritional factors, matrix effects, etc., on protein quality and clear recommendations on practical applications of DIAAS and implications on food supply (e.g., CODEX applications).

Joyce Boye, Ph.D., Agriculture & Agri-Food Canada,,

The summary above is an excerpt from the “2014 Protein Trends & Technology Seminar Magazine: Formulating with Proteins”