1 Determining the appropriate protein intake for older adults is important because inadequate intake contributes to increased risk for common age-associated problems, such as sarcopenia, osteoporosis, and impaired immune responses.15, 16, 17 and 38 The following 3 factors variously influence protein use in older individuals: inadequate intake of protein (eg, anorexia or appetite loss, gastrointestinal disturbances), reduced ability

to use available protein (eg, insulin resistance, protein anabolic resistance, high splanchnic extraction, immobility), or a greater need for protein (eg, inflammatory disease, increased oxidative modification of proteins), all of which point to a need to understand the role of dietary protein in maintaining functionality in older people (Figure 1). find more Epidemiological studies and clinical trials support the need for higher protein intake by older adults. Several epidemiological studies have found a positive correlation between higher dietary protein intake and higher bone mass density39, 40 and 41; slower rate of bone loss42; and muscle mass and strength.43 One epidemiological study showed a positive Apoptosis Compound Library screening association between higher dietary protein intake and fewer health problems in older women.44 With data from the Health, Aging,

and Body Composition (Health ABC) Study, Houston et al14 were able to assess the association between dietary protein intake and changes in lean body mass (LBM) over a 3-year period in healthy, older adults (n = 2066). In this study, dietary protein intake was assessed by using a food-frequency questionnaire; changes in LBM were measured using dual-energy x-ray absorptiometry (DEXA). After adjustment for potential confounders

(eg, demographic characteristics, smoking status, alcohol consumption, physical activity), energy-adjusted protein intake was associated with 3-year Terminal deoxynucleotidyl transferase changes in LBM (P = .004); participants in the highest quintile of protein intake lost approximately 40% less LBM than did those in the lowest quintile of protein intake. These results remained significant even after adjustment for changes in fat mass. Although causality cannot be established, these results do suggest a close relationship between higher protein intake and maintenance of skeletal muscle mass in older adults. Several short-term metabolic studies investigated the differences in protein synthesis and breakdown (both whole-body and skeletal muscle) between younger and older adults.45, 46 and 47 Given the complex nature of the aging process,48 it is not surprising that the combined results of these studies are inconclusive, and sometimes contradictory, for the fasted state.