A new method to digest

Professor Paul Moughan of the Riddet Institute explains why DIAAS should be the preferred method for measuring protein quality

A new method confirms the high bioavailability of dairy proteins and their ability to complement other proteins by being a rich source of dietary essential amino acids. The report by the Food and Agriculture Organization of United Nations (FAO) has recommended a new method for assessing the quality of dietary proteins.

The report, “Dietary protein quality evaluation in human nutrition,” recommends that the Digestible Indispensable Amino Acid Score (DIAAS) replace the Protein Digestibility Corrected Amino Acid Score (PDCAAS) as the preferred method of measuring protein quality. It says that more data be developed to support full implementation, but in the interim, protein quality should be calculated using DIAAS values derived from fecal crude protein digestibility data. Under the current PDCAAS method, values are “truncated” to a maximum score of 1.00, even if scores derived are higher.

Protein is vital to support the health and well-being of human populations. However, not all proteins are alike as they vary according to their origin (animal, vegetable), their individual amino acid composition and the level of amino acid bioactivity. High quality proteins are those that are readily digestible and contain the dietary essential amino acids in quantities that correspond to human requirements.

Three billion added

“Over the next 40 years, three billion people will be added to today’s global population of 6.6 billion. Creating a sustainable diet to meet their nutritive needs is an extraordinary challenge that we won’t be able to meet unless we have accurate information to evaluate a food’s profile and its ability to deliver nutrition,” says Professor Paul Moughan, co-director of the Riddet Institute, who chaired the FAO Expert Consultation.

“The recommendation of the DIAAS method is a dramatic change that will finally provide an accurate measure of the amounts of amino acids absorbed by the body and an individual protein source’s contribution to a human’s amino acid and nitrogen requirements. This will be an important piece of information for decision makers assessing which foods should be part of a sustainable diet for our growing global population.

“The switch over to DIAAS should be straightforward, once information concerning the new method is widely promulgated,” he says. “However, as of today there are insufficient validated ileal amino acid digestibility data available to allow this important aspect of the new DIAAS method to be implemented. This needs to be rectified as soon as possible.

“Research will generate such data for a wide range of proteins and human foods (especially foods in developing nations). Funding for such research is currently being sought and it is hoped the work will begin in the latter half of this year. The work may take one to two years to complete.”

Bioavailability

Using the DIAAS method, researchers are now able to differentiate protein sources by their ability to supply amino acids for use by the body. For example, the DIAAS method was able to demonstrate the higher bioavailability of dairy proteins when compared to plant-based protein sources. Data in the FAO report showed whole milk powder to have a DIAAS score of 1.22, far superior to the DIAAS score of 0.64 for peas and 0.40 for wheat. When compared to the highest refined soy isolate, dairy protein DIAAS scores were 10 per cent to 30 per cent higher.

“The DIAAS describes the ‘quality’ of a protein more accurately,” Moughan notes. “It will thus affect things such as the amount of total protein a manufacturer has to include in a particular food to be able to make a claim concerning protein. Recommendations around the relative rankings of protein sources in terms of quality will change. Critically, in some parts of the world where protein intakes are marginal, diets hitherto considered adequate may now be seen as deficient, and vice versa.”

Health influences

“‘Higher protein’ diets are likely to be seen as more important for weight loss, weight maintenance and the maintenance of lean body mass – all having profound influences for public health – thus the role of dietary protein quality will be central, especially when viewed against a burgeoning world population and a finite food supply. The role of individual dietary amino acids versus total protein is also being increasingly appreciated (eg role of amino acid leucine in maintaining muscle mass), and different proteins supply different amino acids differently (eg dairy protein contains high levels of bioavailable leucine).”

DIAAS determines amino acid digestibility, at the end of the small intestine, providing a more accurate measure of the amounts of amino acids absorbed by the body and the protein’s contribution to human amino acid and nitrogen requirements.

PDCAAS is based on an estimate of crude protein digestibility determined over the total digestive tract, and values stated using this method generally overestimate the amount of amino acids absorbed. Some food products may claim high protein content, but since the small intestine does not absorb all amino acids the same, they are not providing the same contribution to a human’s nutritional requirements.

The PDCAAS method

Since its adoption by FAO/WHO in 1991, the PDCAAS method had been widely accepted but also criticized for a number of reasons. In addition to the issues of truncation and overestimation, PDCAAS did not adequately adjust for foods susceptible to damage from processing and anti-nutritionals, which can make some amino acids unavailable for absorption.

Moughan concludes, “It is critical that we describe dietary protein quality as accurately as possible, and DIAAS is a major step forward and uses the best scientific information currently available. The agrifood industry, FAO and governments are exhorted to support the future work required, such that DIAAS can be used to its fullest extent. This is important to underpin fair trade in proteins, accurate food product claims and to ensure adequacy of protein intakes in the developing countries.”

For further information, please visit www.globaldairyplatform.com