The Total Sulphur Amino Acid Requirement Is Higher in Older Men Than Women

OBJECTIVES: The primary aim of this study was to determine the total sulphur amino acid (TSAA) requirement of adults > 60 years, using the indicator amino acid oxidation (IAAO) method and to compare the requirement estimates between older males and females. The secondary aim was to compare the requirement estimates in older adults to the previously derived IAAO requirement in young males. METHODS: Fifteen healthy older adults (n = 7 male and n = 8 female participants), were randomized to receive 2 to 7 methionine intakes: 5, 10, 15, 19, 25, 35 and 40 mg. kg(−1). d(−1) without dietary cysteine. The TSAA requirement was determined using the IAAO method with L-[1–(13)C]phenylalanine as the indicator. The mean TSAA requirement was determined using two-phase linear mixed effect model, which identified a breakpoint in the F(13)CO(2) in response to graded methionine intakes. The parametric bootstrap method was used to determine the 95% confidence interval (CI). To assess whether the breakpoints were different between older males and females or between older adults and young males the overlap in 95% CI was calculated. The null hypothesis was accepted if the interval contained zero. RESULTS: The mean TSAA requirement for older males was 26.2 mg · kg(−1)· d(−1) and 17.1 mg · kg(−1)· d(−1) for older females. The TSAA requirement of older males is higher than older females (Difference in CI: 9.1 ± 8.85) and higher compared to young males based on our previous IAAO estimate of 12.6 mg · kg(−1)· d(−1) (Difference in CI: 13.6 ± 5.98). CONCLUSIONS: To our knowledge this is the first study to experimentally derive the TSAA requirement in older adults. The results can be used to assess whether the amino acid requirements of older adults can be met on a plant-based diet, especially given the current recommendations for increased plant protein consumption. FUNDING SOURCES: This study was funded by CIHR. First author Alyssa Paoletti funded by Restracomp Scholarship provided by the Research Training Centre at SickKids Hospital.