Amino acids and proteins in relation to the nutrition of elderly people

Abstract

In this short review some aspects of body protein and amino acid metabolism during ageing in human subjects have been explored. The picture that emerges is a progressive diminution of total body protein with ageing, due largely to a decline in the size of the skeletal muscle mass. These changes are accompanied by a shift in the overall pattern of whole body protein synthesis and breakdown, with muscle mass estimated to account for about 30% of whole body protein turnover in the young adult, as compared with a lower value of 20% or less in the elderly subject. The metabolic significance and possible functional implications of this alteration in the quantitative contribution by muscle to whole body amino acid and protein dynamics have been considered. The determination of requirements for individual essential amino acids and for total protein has been discussed, and it is evident that the data are limited and often contradictory. However, elderly individuals are more likely to be influenced by various biological, environmental and social factors, the effects of which would be generally to increase protein needs above those for younger adults. Thus, in practice, the protein needs of elderly people are probably higher than for the young. The decline in energy intake, together with its possible consequences for reduced dietary protein utilization, will also tend to increase the protein need of elderly subjects, compared with that for physically more active young adults. Until more data become available, it is recommended for food planning purposes that an appropriate protein allowance could be 12-14% of the total energy intake, for mixed protein sources characteristic of the diets of industrialized countries or the more affluent sectors of populations in developing countries. Energy intake should be at a level that meets the estimates proposed by FAO/WHO/UNU for older persons. Tentative recommendations are made herein that intakes of specific indispensable (essential) amino acids, per unit of protein need, should be similar to those for the young school-age child and they should be higher than those currently judged by international authorities (i.e. FAO/WHO/UNU) to be sufficient for maintenance of protein nutritional status in the adult. In view of (i) the increasing proportion of older individuals within technically advanced populations together with the need of this group for health care and (ii) the important role played by diet and food habits in health maintenance, and in the aetiology or progression of degenerative disease, it is vitally necessary to improve upon the current state of knowledge concerning protein and amino acid metabolism and nutrition during the later phases of our lives.