Quality of Protein From the Common Bean

Humans require certain minimal quantities of the indispensable amino acids (IAA) from dietary proteins to maintain healthy growth and body function (1). These amino acids are not made in the body and must be provided in the diet. Protein quality is about how dietary proteins can satisfy the body's demand for IAA at various stages of life (1,2) to make different body proteins and biomolecules. It is important to public health and has economic considerations with respect to national food policy, world production and trade in proteins. Uncertainty over the quality of diet, specifically with reference to its protein quality, does potentially impact a nation's health, economy, agriculture and nutrient security. International organizations have begun to address these issues Poor dietary quality has a marked negative impact on the sensitive periods of pregnancy (3) and the first two years of life (the first 1000 days). Furthermore, protein quality is related to stunting which is prevalent in may low and middle income countries because adequate protein quality is required for optimum linear growth. Hence, it is likely to have an impact on the WHO Global Nutrition Target 2025 for reducing the prevalence of stunting (low height-for-age) in children under 5 years by 40%. Stunting has been shown to reduce capacity for learning in children, and hence productivity in adults (4). Of importance, also, stunting increases the risk of developing obesity and chronic non-communicable diseases (CNCD), and therefore plays a role in the impact of CNCD on increasing cost to health and the economy especially in developing countries (5). It is clear that to meet dietary requirements of the IAA, accurate assessment of their availability is essential.

The availability of amino acids from protein sources depends on their amino acids composition and digestibility which have been yardsticks used in the assessment of protein quality. The Food and Agriculture Organization (FAO) in 2011 held an International Symposium on Dietary Protein for Human Health where it was recognized that the current measure of protein availability using oro-faecal nitrogen balance underestimate digestibility because colonic metabolism contributing additional nitrogen to dietary nitrogen is not taken into consideration in the stool loss. The committee concluded that a more robust method of assessing protein quality is needed. Whereas oro-ileal balance is a more accurate method of protein digestibility (6,7), it is an expensive and invasive method, and there is insufficient human data.

Following the symposium in 2011, FAO in 2013 convened a expert consultation meeting and released a report , 'Dietary protein quality evaluation in human nutrition', (8) as part of the call from the United Nations to promote sustainable diets and health and influenced by the 2012 WHO technical note on foods for the management of moderate acute malnutrition in children(9) This report was motivated mainly by advances in methods available to measure the quality of nutritional proteins with more accuracy. It was suggested that a minimally invasive method based on Dual Stable Isotope Tracer approach could be developed to accurately assess protein quality. The IAEA held a Consultants' Meeting in October 2013 to discuss stable isotopic methods to measure protein quality in humans, followed by a FAO Expert Working Group Meeting in March 2014 in Bangalore, to specifically define the most appropriate research methodologies to measure protein digestibility and utilization in humans (10).Hence, the International Atomic Energy Agency (IAEA) has established a Co-ordinated Research Project (CRP) with the aim to develop and validate a novel Dual Stable Isotope Tracer method that is minimally invasive to assess protein digestibility and utilization from plant based diets, as they are consumed by vulnerable populations, in regions habitually relying on plant based diets. Generally, the method is based on the concept that if IAA become labeled with isotope within the food matrix, their appearance in the blood gives a measure of bioavailability, which is independent of other proteins in the food and independent of endogenous body proteins. Comparative tracer appearance in blood of labelled test and reference proteins gives a direct measure of digestion and bioavailability of the test protein. Also, when the reference protein is accompanied by a trace quantity of a differently labelled amino acid such as 13C6-phenylalanine, it will provide an index of amino acids absorption following digestion. We have been awarded an IAEA grant as part of the CRP and proposing to conduct studies in healthy human adults to assess the availability of the IAA from intrinsically labelled common bean (Phaseolus vulgaris) which is among the eight species regarded as global priorities by the Consultative Group for International Agricultural Research (CGIAR, 2012) (11) The research Program includes leveraging legumes to combat poverty, hunger, malnutrition and environmental degradation. Our collaborator from the Scientific Research Council will grow the beans. The amino acids in the bean will be labelled with deuterium, by adding a bolus dose of deuterium oxide to the irrigation water. They have successfully produced labelled beans in a pilot study. To accurately measure IAA availability and protein quality in the common bean will be useful to inform dietary choices consistent with good health The main aim of this study is to develop a minimally invasive method to accurately measure protein quality in the common bean to inform dietary choices consistent with good health. We also, aim to establish an absorption index relative to phenylalanine for use in future studies and to assess utilisation of the protein by measuring protein oxidation and urinary amino acids.

Specific aims are:

1. to characterize the bean protein for isotopic enrichment
2. to quantify bean amino acids made available to the body when the bean and a reference protein are consumed by healthy adults, aged 20 to 45 years.
3. to establish an index for amino acids absorption
4. to determine digestible indispensable amino acids scores