Glycine, a Dispensable Amino Acid, Is Conditionally Indispensable in Late Stages of Human Pregnancy.

BACKGROUND: Recently, we showed that there are higher protein, lysine, and phenylalanine requirements in late stages of pregnancy compared with early stages. Animal studies have suggested an increased dietary need for specific dispensable amino acids in pregnancy; whether such a need exists in human pregnancies is unknown. OBJECTIVE: The objective of the current study was to examine whether healthy pregnant women at midgestation (20-29 wk) and late gestation (30-40 wk) have a dietary demand for glycine, a dispensable amino acid, using the indicator amino acid oxidation method and measurement of plasma 5-oxoproline concentrations. METHODS: Seventeen healthy women (aged 26-36 y) randomly received different test glycine intakes (range: 5-100 mg·kg-1·d-1) during each study day in midgestation (∼26 wk, n = 17 observations in 9 women) and late gestation (∼35 wk, n = 19 observations in 8 women). Diets were isocaloric with energy at 1.7 × resting energy expenditure. Protein was given as a crystalline amino acid mixture based on egg protein composition at current estimated average requirement (EAR; 0.88 g·kg-1·d-1). Breath samples were collected at baseline and isotopic steady state to measure oxidation of L-[1-13C]phenylalanine to 13CO2 (F13CO2). Plasma was collected at the sixth hour of the study day. Linear regression crossover analysis and simple linear regression were used to assess responses in F13CO2 and plasma 5-oxoproline concentrations to different glycine intakes. RESULTS: No statistically significant responses were observed in midgestation. However, in late gestation, lower glycine intakes resulted in higher rates of F13CO2 (suggesting low protein synthesis) with a breakpoint for phenylalanine oxidation at >37 mg glycine·kg-1·d-1 and higher plasma 5-oxoproline (suggesting low glycine availability) with a breakpoint >27 mg glycine·kg-1·d-1. CONCLUSIONS: The findings suggest that glycine should be considered a "conditionally" indispensable amino acid during late gestation, especially when protein intakes are at 0.88 g·kg-1·d-1, the current EAR. This trial was registered at clinicaltrials.gov as NCT02149953.

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

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.

Plasma lutein concentrations are related to dietary intake, but unrelated to dietary saturated fat or cognition in young children.

Lutein and zeaxanthin are xanthophyll carotenoids present in highly pigmented vegetables and fruits. Lutein is selectively accumulated in the brain relative to other carotenoids. Recent evidence has linked lutein to cognition in older adults, but little is known about lutein in young children, despite structural brain development. We determined lutein intake using FFQ, one 24 h recall and three 24 h recalls, plasma lutein concentrations and their association with cognition in 160 children 5·6-5·9 years of age, at low risk for neurodevelopmental delay. Plasma lutein was skewed, with a median of 0·23 (2·5th to 95th percentile range 0·11-0·53) µmol/l. Plasma lutein showed a higher correlation with lutein intake estimated as the average of three 24 h recalls (r 0·479; P = 0·001), rather than one 24 h recall (r 0·242; P = 0·003) or FFQ (r 0·316; P = 0·001). The median lutein intake was 697 (2·5th to 95th percentile range 178-5287) µg/d based on three 24 h recalls. Lutein intake was inversely associated with SFA intake, but dietary fat or SFA intakes were not associated with plasma lutein. No associations were found between plasma lutein or lutein intake and any measure of cognition. While subtle independent effects of lutein on child cognition are possible, separating these effects from covariates making an impact on both child diet and cognition may be difficult.