Nutrition experts from the IAEA, the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization as well as national, research and academic institutions came together recently to outline the framework for a first-of-a-kind protein quality database, to help governments assess the protein adequacy of foods sold to consumers and develop optimal dietary protein requirements.
At the meeting, organized jointly by the IAEA and FAO, they discussed ways of developing the database, which will detail the quality of protein from a variety of foods consumed worldwide.
Welcoming inputs by the experts to inform the future development of the database, Lynnette Neufeld, Director of the FAO’s Food and Nutrition Division, said: “This will greatly aid the evaluation of protein quality and protein sufficiency in different populations.”
The protein quality of a food depends on several factors, including its essential amino acid composition, and their respective bioavailability, in other words how easily the protein source is digested and the proportion of the essential amino acids absorbed by the body for use. From the 20 amino acids that in various combinations make up all proteins, nine are classified as essential, as they cannot be produced by the body and are therefore obtained through protein sources in the diet to support our physiological and developmental needs. The database will contain data on the amount of the essential amino acids – histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine – in food content per 100g, their individual absorption index and the method used to measure the index.
The database will be based on methods recommended by the FAO, including the dual isotope tracer technique (DSIT) – a nuclear technique developed through an IAEA-supported coordinated research project in 2015.
Highlighting the value of including data gathered through the DSIT technique, May Abdel-Wahab, Director of the IAEA Division of Human Health, told meeting participants that the “collection of data on protein quality using novel, accurate methods can provide important information and support policy makers in developing national nutrition programmes.”
The DSIT uses a combination of two isotopic tracers to compare the concentration of amino acids in a blood or breath sample after consuming a meal to the concentration of a standard protein where the digestibility is already known (see the science box below). This ensures the bioavailability of each of the essential amino acids can be accurately calculated.
The next steps in the development of the protein quality database includes bringing the discussions to a broader audience at the International Symposium on Protein and Human Health, to be held in The Netherlands in September 2023 and co-organized by the IAEA and the FAO.
In addition to the work on the new database, two IAEA-supported projects investigating protein quality are currently underway: a regional project in Asia with 16 participating countries, aimed to generate further data on protein quality in this region; and a coordinated research project with seven participating low- and middle-income countries from Asia, Africa and Latin America, evaluating how environmental factors that contribute to chronic gut inflammation or environmental enteric dysfunction influence protein absorption.
The Science
The new dual stable isotope tracer technique measures protein digestion in a minimally invasive way through blood and breath analyses.
In the first phase of the technique, amino acids in test food for humans are labelled using the stable isotope deuterium, a form of hydrogen. Deuterium, which is harmless, is added to animals’ drinking water to study animal protein sources, and to irrigation water for plant-based sources such as vegetables. Then, once the milk or legumes, for example, are ready for consumption, these deuterium-labelled foods are eaten by human volunteers along with a reference protein source labelled with carbon-13, a stable isotope of carbon.
In the second phase, blood and breath samples are collected before and several times after the meal has been consumed to analyse amino acid concentration. Digestibility is determined by the ratio of the labelled amino acids in the blood to those in the test meal. The recovery of carbon-13 from the breath samples provides a second indicator of protein digestion.
