Sarcopenia is defined as the age-associated loss of skeletal muscle mass and function. After age 30, people lose approximately 3%-8% of their muscle mass each decade. This occurs due to many factors, but is commonly attributed to a sedentary lifestyle and inadequate protein intake. Progressive muscle loss can ultimately lead to reduced metabolism and increased frailty. Though research in this area is preliminary, scientists have agreed that moderately increasing daily protein intake beyond the Recommended Daily Allowance (0.8g/kg/d) may enhance muscle protein anabolism and provide a means of reducing the progressive loss of muscle mass with age. Other methods of reducing muscle loss include regular strength training, although the benefits of this in an aging population have been inconclusive. More research is needed to specify an optimal value of protein ingestion, although shooting above the RDA appears to be advantageous for now.
Source: Paddon-Jones et al. Role of dietary protein in the sarcopenia of aging. Am J Clin Nutr. 2008; 87(suppl):1562S– 6S.