Dietary protein requirements of younger and older adults

Background: For older men and women, the Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) for protein are not known with confidence. Data from the limited research studies available suggest that the EAR and RDA might be greater than the assumed 0.66 and 0.80 g protein . kg body wt(-1) . d(-1), respectively. Objective: This study assessed the effect of age on the EAR and RDA for protein. Design: Twenty-three younger (age: 21-46 y; 11 men, 12 women) and 19 older (age: 63-81 y; 8 men, 11 women) persons completed three 18-d trials with protein intakes of 0.50, 0.75, and 1.00 g protein . kg body wt(-1) . d(-1). Nitrogen balance was determined by using data from total nitrogen analyses of duplicate food composites and complete urine and feces collections from days 14 to 17 of each trial. Each subject's protein requirement was estimated by using linear regression of protein intake and nitrogen balance data from all 3 trials and inverse prediction. Results: The mean (+/- SD) protein requirement was not different between the younger and older subjects: 0.61 +/- 0.14 compared with 0.58 +/- 0.12 g protein . kg body wt(-1) . d(-1). On the basis of individual requirement estimates from the younger and older subjects combined (2.5% trimming from each tail and variation estimated by the bootstrap), an adequate protein allowance for these subjects was calculated to be 0.85 +/- 0.21 g protein . kg body wt(-1) . d(-1). Conclusions: These short-term nitrogen balance results suggest that the requirement for total dietary protein is not different for healthy older adults than for younger adults and that the allowance estimate does not differ statistically from the RDA. Am J Clin Nutr 2008; 88: 1322-9.