Methionine Requirements in Early and Late Stages of Healthy Canadian Pregnancies in the Presence of Cysteine Determined Using the Indicator Amino Acid Oxidation Method.

BACKGROUND

Recently, total sulfur amino acid (TSAA; methionine + cysteine) requirements during pregnancy were found to be 11.1 and 15.0 mg/kg/d in early and late gestation, respectively. Methionine requirements in the presence of cysteine during pregnancy are unknown.

OBJECTIVES

The objective of this study was to determine methionine requirements in the presence of dietary cysteine during early (11-20 wk) and late (31-40 wk) gestation in healthy females with singleton pregnancies and to examine if differences in requirements exist between early and late gestation using the indicator amino acid oxidation (IAAO) technique.

METHODS

Twenty-three females aged 26 to 39 y with a healthy singleton pregnancy were studied using the IAAO technique in a repeated measures design for a total of 61 study days. On each study day, a methionine test intake (range: 0-15 mg/kg/d) was provided in 8 hourly, isonitrogenous and isocaloric meals with cysteine provided at 25 mg/kg/d. Breath samples were collected at baseline and isotopic steady state with oral provision of L-1-13C-phenylalanine for measurement of phenylalanine oxidation. Requirement was determined using a biphasic linear mixed-effects model to identify a breakpoint in 13CO2 production, representing the estimated average requirement (EAR).

RESULTS

Methionine requirement in healthy pregnant participants in early gestation was 7.9 mg/kg/d (R2m = 0.68, R2c = 0.75; 95% CI: 5.0, 10.8 mg/kg/d) and 9.1 mg/kg/d (R2m = 0.84, R2c = 0.91; 95% CI: 7.4, 10.8 mg/kg/d) in late gestation. Difference between confidence intervals of the 2 breakpoints was = -1.2 ± 3.3, and not statistically different.

CONCLUSIONS

Methionine EAR during early and late pregnancy are 7.9 and 9.1 mg/kg/d, respectively. These methionine needs represent 71% and 61% of mean TSAA requirements of 11.1 and 15.0 mg/kg/d in early and late gestation, respectively, as previously determined, suggesting that methionine needs are substantial throughout pregnancy. This trial was registered at clinicaltrials.gov as NCT04326322.