Amino acid metabolism and regulatory effects in aging

PURPOSE OF REVIEW: To examine recent discoveries related to the amino acid metabolism and regulatory effects in aging, focusing on the development and treatment of age-related muscle loss (sarcopenia). RECENT FINDINGS: While basal amino acid metabolism may be unaffected by age, elderly subjects appear to have a decreased ability to respond to anabolic stimuli such as insulin and, to a lesser extent, amino acids. Specifically, compared to young subjects, the stimulation of muscle protein synthesis is attenuated in elderly subjects following the administration of mixed meals due to insulin resistance. In addition, the anabolic effect of amino acids appears blunted at low doses. Recent studies, however, have highlighted that these age-related alterations in amino acid metabolism may be overcome by provision of excess leucine, changes in the daily protein intake pattern or exercise, which improve activation of translation initiation and muscle protein synthesis. SUMMARY: Muscle loss with aging is associated with significant changes in amino acid metabolism, which can be acutely reversed using nutritional manipulations and exercise. Long-term, large clinical trials are, however, needed to determine the clinical significance of these findings in the elderly population, and to establish if nutritional and exercise interventions can help prevent and treat sarcopenia.