Dietary Lysine Requirement of Women Over 60 Years Estimated Using Indicator Amino Acid Oxidation (IAAO) Technique, Is Not Different From Current Recommendations

OBJECTIVES: The goals of the current study were to 1) define the lysine requirement in female adults >60years using the indicator amino acid oxidation method (IAAO) method with L-[1–(13)C]phenylalanine as the indicator and to 2) compare the derived estimate to our previous estimates in young women done in both luteal and follicular phase of the mensural cycle. METHODS: Sixteen healthy women (>60 years) 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 on day 3. The rate of release of(13)CO(2) from the oxidation of L-[1–(13)C]phenylalanine was measured in breath. A two-phase linear mixed effect model, and parametric bootstrap was used to determine the mean and 95% confidence interval (CI) of the lysine requirement. The overlap of the 95% CI between the older and younger women 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 of older women was 29 and 33 mg(.)kg(−1.)d(−1)respectively. This was not different from our previous estimate of 30.9 mg(.)kg(−1.)d(−1)for young women in the follicular phase of the mensural cycle. However, it was lower than our previous estimate of 37.7 mg(.)kg(−1.)d(−1)derived during the luteal phase of the mensural cycle. CONCLUSIONS: This is the first study to report on the lysine requirement in older women >60 years. Although the estimate in older women is not different from current recommendations derived in young men, the results suggest that lysine requirement in young and older women may differ based on mensural cycle phase. FUNDING SOURCES: CIHR.