Dietary lysine requirements of older adults stratified by age and sex.

Background Current recommendation for lysine in older adults, 30 mg. kg−1.d−1, is based on young adult data. Evidence suggests that amino acid requirements may differ between young and old adults with both sex and age having an effect in the elderly Objectives 1) Define the lysine requirements in healthy older adults using the indicator amino acid oxidation (IAAO) method with L-[1-13C]phenylalanine as the indicator and 2) compare the derived estimates based on age: 60-69y and >70y Methods Fourteen healthy males and 16 healthy females (> 60y, BMI=26.3 kg.m-2) were randomly assigned to receive 3 to 7 lysine intakes from 10 to 80 mg. kg−1. d−1. Subjects were adapted to a standard liquid diet providing 1.0 g. kg−1.d−1 protein and adequate energy, for 2 days, with indicator oxidation measurements performed on day three. The rate of release of 13CO2 from the oxidation of L-[1-13C] phenylalanine was measured in breath. A two-phase linear mixed effect model, and parametric bootstrap were used to determine mean lysine requirements and the 95% confidence intervals (CI). The overlap of the 95% CI between the 2 age groups were used to compare the requirement estimates. The null hypothesis was accepted if the interval contained zero Results The mean and upper 95% CI of the lysine requirement for females were 32.9 and 40.9, and 46.2 and 53.7 mg. kg−1.d−1 for those 60-69 and >70y, respectively. The mean and upper 95% CI of the lysine requirement for the 2 groups of males were not different, so was combined to yield a mean and 95% CI of 32.2 and 38.2 mg. kg−1.d−1 Conclusions This is the first study to report on the lysine requirement in older adults >60y. These results provide a basis from which the adequacy of diets to meet lysine needs of older adults can be assessed. The trial was registered at Clinical Trials Registry # NCT02008955, https://clinicaltrials.gov/study/NCT02008955