(PTFS03-03-24) Dietary Tryptophan Requirements in Human Pregnancy Are Higher Than Current Recommendations

Objectives: Our primary objective was to use the Indicator Amino Acid Oxidation (IAAO) method to estimate the dietary requirement for tryptophan, an essential amino acid, in female pregnancies. We hypothesized that the dietary requirement for tryptophan will be different compared to current dietary reference intake (DRI) recommendations.

Methods: Our experimental design was based on the minimally invasive IAAO protocol. Participants’ eligibilities were determined during the preliminary assessment day based on anthropometric measurements, biochemical, dietary assessments and brief clinical history. Five healthy singleton pregnant females (28-40y) received graded tryptophan intakes (1-14 mg/kg/d) in random order. Diets were provided as isocaloric and isonitrogenous meals that consist of a liquid protein shake with (L-[1-¹³C] phenylalanine) tracer and protein-free cookies, >with adequate energy and protein. On study days, meals were consumed hourly, beginning 4 hrs before the introduction of the tracer (L-[1-¹³C]phenylalanine) and 4 hours with tracer, to ensure metabolic steady state. Breath samples were collected at baseline and isotopic steady state and analyzed for expired (¹³CO₂) enrichment using a continuous-flow isotope ratio mass spectrometer. The estimated average requirement (EAR) of tryptophan was statistically determined using breakpoint analysis on the effect of different tryptophan intakes on breath ¹³CO₂ values with a two-phase linear regression crossover model.

Results: Preliminary analysis suggests tryptophan requirement during late-stage pregnancy of 6.2 mg/kg/d (R²_m=0.63, R²_c=0.75; 95%CI: 3.9 – 8.4 mg/kg/d. This is 24% higher than current EAR of 5 mg/kg/d, and approximately 54% higher than previously determined tryptophan requirement of 4.01 mg/kg/d> in non-pregnant females.

Conclusions: This is first study to use a stable isotope–labeled amino acid technique to determine tryptophan dietary requirements in pregnant population. The findings that tryptophan needs are higher (24%) than the current DRI recommendations will help optimize dietary guidelines during pregnancy for improving maternal and fetal health.

Funding Sources: Canadian Institute of Health Research (CIHR)