Protein turnover and requirements in the healthy and frail elderly

There are as yet no definitive data that warrant the establishment of evidence-based dietary protein recommendations for the elderly. We reviewed the relevance of the new 2002 recommended protein intake of 0.80 g/kg body weight.d for adults to healthy and frail elderly persons. We found that data from published nitrogen balance studies indicate that, a higher protein intake of 1.0 - 1.3 g/k.d is required to maintain nitrogen balance in the healthy elderly, which may be explained by their lower energy intake and impaired insulin action during feeding compared with young persons. Although it needs to be confirmed, a decrease in efficiency of protein utilization with aging may also dictate a higher protein-intake recommendation. Measures of the dynamic aspects of protein metabolism done in the postabsorptive state have shown no change in whole body protein turnover per unit of active metabolic tissue with aging. However, the contribution of muscle protein to wholebody protein metabolism was significantly reduced in the elderly, and explained by their reduced muscle mass and lower rates of myofibrillar protein turnover. Consequently, the contribution of nonmuscle protein, especially that of visceral tissue whose rates of protein turnover are known to be more rapid was proportionally greater with aging. It is conceivable that higher protein consumption rates could compensate for the decrease in availability of muscle amino acids and spare the muscle mass. Despite a paucity of data on the frail elderly population, we present a rationale to justify a greater protein intake of at least equivalent to that of their healthy counterparts. We propose that higher protein intakes for the elderly, and especially the frail population, than those presently recommended may minimize the sarcopenia of aging and thereby protect against some of the health risks of aging.