(P07-051-23) Total Sulfur Amino Acid Requirements Are Higher in Late Gestation Compared to Early Gestation During Healthy Human Pregnancy

Objectives: The aim of this study was to determine total sulfur amino acid (TSAA; methionine, an essential amino acid + cysteine, conditionally essential amino acid) requirements in healthy human pregnancy in early (11-20 weeks) and late (31-40 weeks) gestation using the indicator amino acid oxidation (IAAO) method.

Methods: Twelve (mean±SD; 33.1 ± 4.0y, pre-pregnancy BMI= 23.0, ± 3.4 kg/m²) and thirteen (32.5 ± 3.7y, pre-pregnancy BMI=22.6, ± 3.0 kg/m²) women were studied in early and late gestation, respectively. Using the stable isotope-based IAAO technique in a repeated measures design, a total of 30 study days were completed in early gestation and 40 study days were completed for late gestation. Methionine intakes (0, 5, 10, 15, 20, 30, 35 and 40 mg/kg/day) were provided in eight hourly, isonitrogenous and isocaloric meals with cysteine excluded from the diet. Breath samples were collected at baseline, and isotopic steady state of orally provided 1-¹³C-Phenylalanine. Samples were analyzed for ¹³C enrichment. TSAA requirement was determined using two-phase linear regression crossover analysis to identify a breakpoint in ¹³CO₂ production, representing two separate minimum dietary requirements for each gestational stage.

Results: Results indicate the estimated average requirement (EAR) for TSAA requirement in early gestation to be 11.1 mg/kg/day [R² 0.78, 95% CI: 8.6, 13.5] and in late gestation to be 16.7 mg/kg/day [R² 0.67, 95% CI: 13.3, 20.2] (p= < 0.01).

Conclusions: We have directly measured TSAA requirements in pregnant mothers in both early and late gestation for the first time. Our values for early and late gestation are 45% and 17% lower, respectively, compared to current Dietary Reference Intakes EAR of 20 mg/kg/day during pregnancy. Current recommendations are factorially calculated which may not be appropriate. Interestingly, we show that TSAA needs are statistically different and increase by 50% by late gestation compared to early gestation, which suggests stage specific dietary recommendations are necessary.

Funding Sources: Research supported by Canadian Institutes of Health Research (CIHR)