Dietary Leucine Requirement Of Older Men And Women Is Higher Than Current Recommendations

Background: Current national (34 mg kg(-1) . d(-1)) and international (39 mg kg(-1) . d(-1)) recommendations for leucine in older adults are based on data from young adults. Evidence suggests that the leucine requirements of older adults are higher than those of young adults.Objective: The objective of the current study was to directly determine the leucine requirements in healthy older adult male and female study participants aged >60 y.Methods: Leucine requirement was determined using the indicator amino acid oxidation method (IAAO) with L-[1-C-1(3)]phenylalanine as the indicator. Sixteen older adults (n = 7 male and n = 9 female participants) were randomly assigned to receive 3 to 7 leucine intakes from 20 to 120 mg . kg(-1) . d(-1). The rate of release of (CO2)-C-13 from L-[1-C-13]phenylalanine oxidation was measured, and breakpoint analysis was used to estimate the leucine requirement. The 95% CI was calculated using the parametric bootstrap method.Results: The mean leucine requirement for male participants was 77.8 mg . kg(-1) . d(-1) (upper 95% CI: 81.0) and for female participants, it was 78.2 mg . kg(-1) . d(-1) (upper 95% CI: 82.0) with no sex effect based on body weight. The data were therefore combined to yield a mean of 78.5 mg . kg(-1) . d( -1) (upper 95% CI: 81.0 mg . kg(-1) . d(-1)) for both sexes. On the basis of fat-free mass, the mean +/- SEM leucine requirements were 115 +/- 3.2 and 127 +/- 2.4 mg . kg(-1) . d(-1) for male and female participants, respectively (P < 0.005).Conclusions: The estimated leucine requirement of older adults is more than double the amount in current recommendations. These data suggest that leucine could be a limiting amino acid in the diet of older adults consuming the current RDA for protein and those consuming a plant-based diet. In view of the functional and structural role of leucine, especially its importance in muscle protein synthesis, current leucine recommendations of older adults should be revised.