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

Authors
  • Rasmussen, Betina F1, 2
  • Ennis, Madeleine A1, 2
  • Dyer, Roger A1, 3
  • Lim, Kenneth1, 4
  • Elango, Rajavel1, 2, 5
  • 1 BC Children's Hospital Research Institute, Vancouver, British Columbia, Canada. , (Canada)
  • 2 Department of Pediatrics, University of British Columbia, Vancouver, British Columbia, Canada. , (Canada)
  • 3 Analytical Core for Metabolomics and Nutrition (ACMaN), BC Children's Hospital Research Institute, Vancouver, British Columbia, Canada. , (Canada)
  • 4 Department of Obstetrics and Gynecology, University of British Columbia, Vancouver, British Columbia, Canada. , (Canada)
  • 5 School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada. , (Canada)
Type
Published Article
Journal
Journal of Nutrition
Publisher
Oxford University Press
Publication Date
Feb 01, 2021
Volume
151
Issue
2
Pages
361–369
Identifiers
DOI: 10.1093/jn/nxaa263
PMID: 32939556
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

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. 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. 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. 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. 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. Copyright © The Author(s) on behalf of the American Society for Nutrition 2020.

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