The dietary requirement for total sulfur amino acids in adults aged ≥60 years appears to be higher in males than in females

Background: The total sulfur amino acid (TSAA) recommendation in older adults is based on data from young adults. Physiological evidence suggests that older adults have a higher requirement than young adults.

Objectives: The objective of this study was to determine the TSAA requirement in healthy men and women aged ≥60 y.

Methods: The TSAA requirement was determined using the indicator amino acid oxidation method with L-[1-¹³C]phenylalanine as the indicator. At recruitment, 15 older adults (n = 7 men and n = 8 women; BMI < 30 kg/m²) were assigned to receive 7 methionine intakes (5, 10, 15, 19, 25, 35, and 40 mg/kg/d) without dietary cysteine. Intake levels were randomly assigned to each subject. Following enrollment, 2 subjects completed 2 intakes and 3 completed 3, while the remainder completed all 7. Mean TSAA requirement was determined from oxidation of L-[1-¹³C]phenylalanine using a mixed-effect change-point model. The 95% CI was calculated using parametric bootstrap. To test whether breakpoints were different between men and women, the overlap in the 95% CI was calculated.

Results: The mean TSAA requirement was 26.2 (R_m² = 0.39, R_c² = 0.89; P < 0.001) and 17.1 mg/kg/d (R_m² = 0.22, R_c² = 0.79; P < 0.001) for men and women, respectively. The requirement was significantly higher in men than in women (difference in CI: 9.1 ± 8.85).

Conclusions: To our knowledge, this is the first study to determine the TSAA requirement in older adults. The requirement in older women is similar to current recommendations but is 75% higher in older men. These findings are important given recommendations for increased plant protein consumption. They will help in the assessment of diet quality and provide the basis of dietary guidelines for older adults consuming a plant-based diet. This trial was registered at clinicaltrials.gov as NCT04595188.