Dietary phenylalanine requirements during early and late gestation in healthy pregnant women

Abstract

Background Phenylalanine is an indispensable amino acid and, via tyrosine, is the precursor for the neurotransmitters dopamine, norepinephrine, and epinephrine. Currently, dietary requirements for phenylalanine during pregnancy are unknown. Objectives This study's aim was to determine phenylalanine requirements (in the presence of excess tyrosine) during early and late gestation using direct amino acid oxidation (DAAO; with l-[1-13C]phenylalanine) and indicator amino acid oxidation (IAAO; with l-[1-13C]leucine). Methods Twenty-three healthy women (age: 30.4 ± 3.1 y, mean ± SD) were studied at a range of phenylalanine intakes (5.5–30.5 mg · kg−1 · d−1 in early and late pregnancy using DAAO, and 2.5–30.5 mg · kg−1 · d−1 in late pregnancy using IAAO) for a total of 76 study days. Test intakes were provided as 8 isocaloric and isonitrogenous meals with 1.5 g · kg−1 · d−1 protein and energy at 1.7 times the measured resting energy expenditure. Breath samples were analyzed on an isotope ratio mass spectrometer for 13C enrichment. Phenylalanine requirement was determined using a 2-phase linear regression crossover model to identify a breakpoint in 13CO2 production (representing the mean requirement) in response to phenylalanine intakes. Results Phenylalanine requirement during early pregnancy was determined to be 15 mg · kg−1 · d−1 (95% CI: 10.4, 19.9 mg · kg−1 · d−1); during late pregnancy, it was determined to be 21 mg · kg−1 · d−1 by DAAO (95% CI: 17.4, 24.7 mg · kg−1 · d−1) and IAAO (95% CI: 10.5, 32.2 mg · kg−1 · d−1). Conclusions Our results suggest a higher requirement (40%) for phenylalanine during late pregnancy than during early pregnancy. Moreover, the early pregnancy requirements are higher than the previous adult male requirement (9.1 mg · kg−1 · d−1; 95% CI: 4.6, 13.6 mg · kg−1 · d−1), although the 95% CIs overlap. Both DAAO and IAAO methods provided similar breakpoints in late pregnancy, showing that the DAAO method was appropriate even though low phenylalanine intakes could not be tested. These results have potential implications for gestation stage–specific dietary phenylalanine recommendations in future. This trial was registered at clinicaltrials.gov as NCT02669381.

Maternal Serum Albumin Redox State Is Associated with Infant Birth Weight in Japanese Pregnant Women

“…Lastly, a recent study on healthy pregnant women in Canada reported that the protein requirement could be higher than the current DRI recommendation [ 39 ]. The same research group subsequently showed increased requirements of specific indispensable amino acids, such as lysine and phenylalanine, during pregnancy [ 40 , 41 ]. Thus, caution may be necessary to view the risk of FGR and LBW in the context of maternal protein intake.…”

Antihypertensive effect and underlying mechanism of tripeptide NCW on spontaneously hypertensive rats using metabolomics analysis

“…91 Phenylalanine could be converted into tyrosine in the body, and tyrosine is a precursor to the norepinephrine, epinephrine, and dopamine. 92 High levels of these stress hormones are associated with the increased risk of hypertension. 93 N-(Linolenoyl) tyrosine is an α-amide conjugate between α-linoleate and the tyrosine.…”

Comparison of phenylalanine tolerance in singleton and twin pregnancies in patients with phenylketonuria

“… *The mean value was from 13 to 19 weeks of pregnancy according to Ennis et al. 13 who proposed intervals called early and late pregnancy. We adopted these intervals because of late implementation of a low-Phe diet from 15 to 19 weeks in the singleton pregnancy of patient 2.…”

“… 13 These authors showed that the minimum daily Phe requirement was 15 mg (95% confidence interval: 10.4–19.9 mg) in early pregnancy (13–19 weeks’ gestation) and 21 mg (95% confidence interval: 17.4–24.7 mg) in late pregnancy (33–39 weeks’ gestation). In early pregnancy, as well as in late pregnancy, our Phe tolerance estimates are consistent with data by Ennis and colleagues 13 only in patient 1. In the other patients, the estimated Phe tolerance was less than the minimum demand as calculated by direct amino acid oxidation.…”