Quality trumps quantity: Why DIAAS is the preferred protein model

When it comes to protein, you have to look beyond quantity alone. This is why the FAO-recommended DIAAS (digestible indispensable amino acid score) method should become the gold standard for protein quality measurement.

Paul Moughan
Paul Moughan Distinguished Professor at Massey University and Riddet Institute Fellow Laureate
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Published: Jul. 01. 2020

Protein is in the spotlight for various reasons, including weight management, addressing the needs of an aging population, and of course for its sports performance potential. High protein diets such as paleo are proving to be all the rage, as a greater understanding emerges around protein’s satiety benefits for weight management. There is strong recognition that as people age, they will lose muscle mass and must compensate for this by consuming more protein. At the same time, the need for protein in muscle building and recovery is embedded into every sports nutrition regimen. 

But not all proteins are created equal. Milk, whey, meat, eggs and well-processed soy have well-balanced amino acids that are highly digestible and bioavailable. However, other proteins such as some cereals, beans and animal proteins such as collagen, have less well-balanced amino acid patterns and are less well digested, and the amino acids are less well absorbed.

As headlines proliferate around the need to supply protein to an ever-growing global population, the common argument has emerged that people around the world are already consuming more than they need. While this may indeed be true in terms of total protein, it is unfortunately not the case when it comes to their intake of available protein. For example, a child in India consuming a diet that is heavily based on cereals and root crops, may be getting plenty of protein containing foods, but they could still be heavily deficient in available protein. This deficiency can lead to stunted growth during childhood and result in them never fulfilling their true potential. 

If you really want to talk about protein in an educated way and form logical debates, you have to look beyond quantity alone. You must also factor quality into the debate, through the use of a reliable method. This is why there is growing consensus that the Food and Agriculture Organization of the United Nations (FAO) recommended DIAAS (digestible indispensable amino acid score) measurement method should become the gold standard for protein quality measurement in the future. 

DIAAS comes to the fore
Protein scoring systems are used to compare a protein’s relative quality as a source of amino acids for the body. 

In the past, the globally recommended scoring method was the protein digestibility corrected amino acid score (PDCAAS), which is still used in major countries, including the US. But this approach has its shortcomings, none more so than the problematic rat faecal methodology i.e. the rat is not a good model for humans and faecal testing is also not valid scientifically. As a result, PDCAAS tends to overestimate the value of lower quality proteins.

Realising the limitations of PDCAAS, the FAO Expert Consultation, recommended a new score to replace PDCAAS in 2013, called DIAAS. This method requires true ileal amino acid digestibility estimates, based on measuring undigested amino acids at the end of the small intestine. Since you cannot routinely make those measurements in humans, an alternative model for protein digestion between the mouth and the end of the small intestine, is required. As the chair of the FAO Expert Consultation, my expert panel proposed the use of the growing pig as the preferred model to generate “predicted human” digestibility values. 

When proposed, we had already conducted pig model studies for three types of protein and found close agreement between the species. However, while the consensus at the FAO consultation was that these studies did demonstrate the model’s accuracy, more data were deemed necessary to confirm the inter-species agreement. Also, it was concluded that there were insufficient data on ileal amino acid digestibility. This view was echoed by several Codex committees, including one on infant formula. All were confident on the method, but just wanted a larger body of supporting data.

The dawn of Proteos
With this background, the Proteos project was established by a consortium of the world’s food sectors to develop further comprehensive true ileal amino acid digestibility and DIAAS data for foods. The ongoing project is overseen on behalf of the food sector funders, by the Global Dairy Platform (GDP), headquartered in Chicago. There is also a consortium of research providers involved, which include Wageningen University and Research (the Netherlands); AgroParisTech (France); the Riddet Institute, Massey University (New Zealand), and the University of Illinois, (USA). 

The first part of the project, which started in early 2018, involved further demonstrating that the growing pig held up as a good and reliable model for human ileal amino acid digestibility. Our work resulted in a further eight protein containing foods being researched across the protein quality spectrum; from low digestibility (e.g. bean and sorghum) up to very high (e.g. whey protein isolate). In each case, the model held up. This work further validated the model as a good methodology for measuring DIAAS and it now provides a springboard to use for generating a large dataset for foods. New DIAAS values have already been published for some 90 human foods.

The second phase of the study involves expanding the range of key protein-containing foods, to form a consistent database. Once funding has been fully confirmed, the next phase will likely commence in the third quarter of this year. It will involve calculating the true ileal amino acid digestibility and the DIAAS values for 100 common protein containing foods, to add to the body of evidence already out there. 

It’s important to stress that the significance of confirming the pig as a model is greater than the sum of the Proteos research alone. There is a wealth of literature available in foods for many values of true ileal amino acid digestibility that have been determined in pigs, some of which are consumed by humans. Now that this model has been validated, a lot of historical data will open up for DIAAS scores, making more food comparisons possible.

The second phase of Proteos is only expected to last about a year, after which sufficient data will be available for the FAO and Codex teams to affect its broad application. All along the way, our consortium of researchers will be on board to offer practical advice.

Taking DIAAS into the mainstream
The implications of the widespread adoption of a DIAAS protein quality model are great. 

Protein is often costed in terms of quantity rather than quality. Much more valuable, however, would be to place a cost per unit on the available levels of protein. This will now be possible once a DIAAS model has been adopted. Furthermore, for a product manufacturer looking to make a protein claim on a food, high protein beverage or supplement, communicating around the amount of available protein, could be more accurately interpreted once a DIAAS model can be applied. 

Work in this area should be of advantage to the dairy sector, as the model will prove that certain dairy proteins, including whey protein isolate and casein, are almost 100 percent digested. Whey is one of the highest quality proteins around and the rise of DIAAS will present an opportunity to promote that composition and the science that underpins it. For example, the DIAAS values for whey protein concentrates are usually greater than 1.10, while for whey protein isolates, they can reach 1.30. Some plant proteins will only weigh in at around 0.70, however. 

But it doesn’t need to be a matter of either/or. DIAAS will spell huge potential for combining different proteins to achieve optimal amino acid profiles. This issue will be discussed in my next blog. 

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