Total sulfur amino acid requirements are higher during late gestation compared with early gestation in healthy Canadian pregnancies in a repeated-measures trial

Background: Dietary Reference Intake (DRI) Recommendations for total sulfur amino acids (TSAAs; methionine + cysteine) during pregnancy are based on factorial calculations using data from adult males. To date, no data exist on TSAA requirements obtained directly during pregnancy.

Objectives: The objective of this study was to examine whether TSAA requirements during early (11-20 wk) and late (31-40 wk) gestation in healthy females with singleton pregnancies are different than current recommendations, and different between early and late gestation using the indicator amino acid oxidation (IAAO) technique.

Methods: Twenty-five females 20-40 y with a healthy singleton pregnancy were studied using the IAAO technique in a repeated measures design for a total of 70, 8-h d. On each study day a methionine test intake (range: 0-40 mg⋅kg^-1⋅d^-1) was provided in 8 hourly, isonitrogenous and isocaloric meals with cysteine excluded from the diet. Breath samples were collected at baseline and isotopic steady state of orally provided L-1-¹³C-Phenylalanine for measurement of phenylalanine oxidation. The requirement was determined using biphasic linear regression crossover analysis to identify a breakpoint in ¹³CO₂ production, representing the estimated average requirement (EAR).

Results: The TSAA requirement in healthy pregnant participants in early gestation was 11.1 mg⋅kg^-1⋅d^-1 {R²_m = 0.79, R²_c = 0.79; 95% confidence interval [CI] (8.9, 13.3 mg⋅kg^-1⋅d^-1)} and 15.0 mg⋅kg^-1⋅d^-1 (R²_m = 0.72, R²_c = 0.79; 95% CI [13.0, 17.0 mg⋅kg^-1⋅d^-1]) in late gestation. The difference between confidence intervals of the 2 breakpoints was = -3.9 ± 3.0, and statistically different.

Conclusions: We directly measured TSAA requirements in healthy pregnant mothers, and our findings suggest that requirements are lower than current DRI recommendations of 20 and 25 mg⋅kg^-1⋅d^-1, as the EAR, and Recommended Dietary Allowance, respectively. Late gestation TSAA needs are significantly different and increased 35% compared with early gestation. Recommendations for TSAA intake need to be tailored for gestational stage. This clinical trial was registered at clinicaltrials.gov as NCT04326322.