Chronic malnutrition: protein metabolism

The topic of protein metabolism in chronic malnutrition is very broad and it seems appropriate to select a single issue which at the present is the subject of a controversy with widespread implications for policy and, hence, the health and well-being of large sectors of the population.The controversy centres on our understanding of the minimum requirements for protein and, therefore, deals with a number of fundamental issues.One of the questions raised, but not answered, by the controversy is the extent to which nutritional science can aspire to being value free.Last year an article by Young & Pellett (1990) appeared in the Food and Nutrition Bulletin, with the title 'Current concepts concerning indispensable amino acid needs in adults and their implications for international nutrition planning'.The content of the paper had been promised since the most recent Food and Agriculture Organization (FAO)/World Health Organization (WHO)/United Nations University (UNU) expert consultation on protein and energy requirements (Food and Agriculture Organization/ World Health OrganizationAJnited Nations University, 1985) for Young had served notice of its advent for some years (Young & Bier, 1987).The recommendations for protein in the FAO/WHO/UNU document were based on the results of studies around the world using a standard N balance technique.There was general agreement on the desirability of developing more precise approaches to the definition of protein and amino acid requirements.Since 1985, Young's group in particular has published a series of papers in the scientific literature in which I3C-labelled probes have been used to trace the fate of the carbon skeletons of the indispensable amino acids.The results of these studies led Young to the conclusion that the dietary requirement for the indispensable amino acids for normal healthy adults has been grossly underestimated by a factor of between two and three.Hence, the recommendations on the quality of dietary proteins which should be ingested to support requirements is unsafe.The conclusion has been reached that the requirements for essential amino acids cannot be met on diets which are based on cereals unless: (a) ar least 30% of the total protein is derived from animal sources, or (b) at least 40% of the total protein is derived from animal sources plus pulses and soya beans (Young & Pellett, 1990).If the pattern for essential amino acids proposed by Young (Young & Pellett, 1990) were to be used as the basis for assessing the needs for protein in the world there would