Total-body protein turnover in parenterally fed neonates: effects of energy source studied by using [15N]glycine and [1-13C]leucine

Am J Clin Nutr. 1989 Dec;50(6):1395-400. doi: 10.1093/ajcn/50.6.1395.


The effects of nonprotein energy source (ie, glucose only vs glucose and lipid) on nitrogen retention and total-body protein turnover were studied in 20 parenterally fed newborn infants. All infants received approximately 3 g amino acids and 80-90 body wt.d. Total-body protein synthesis was estimated by using three constant-infusion, end-product methods: enrichment of urinary urea and ammonia in response to a [15N]glycine label and exhaled carbon dioxide enrichment in response to a [1-13C]leucine label. No differences were seen in nitrogen retention between the two energy sources. The estimate of total-body protein turnover obtained from the 13C label was similar to that obtained with the [15N]urea label. No differences in turnover rates were observed between the two diet groups. Use of the glucose-plus-lipid fuel system enhanced energy storage and the reutilization of amino acid for protein synthesis.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ammonia / urine
  • Carbon Dioxide / analysis
  • Carbon Isotopes
  • Energy Intake
  • Energy Metabolism*
  • Fat Emulsions, Intravenous / administration & dosage
  • Fat Emulsions, Intravenous / metabolism
  • Glucose / administration & dosage
  • Glucose / metabolism
  • Glycine / metabolism*
  • Humans
  • Infant, Newborn / metabolism*
  • Leucine / administration & dosage
  • Leucine / metabolism*
  • Nitrogen / metabolism
  • Nitrogen Isotopes
  • Parenteral Nutrition*
  • Proteins / metabolism*
  • Urea / urine


  • Carbon Isotopes
  • Fat Emulsions, Intravenous
  • Nitrogen Isotopes
  • Proteins
  • Carbon Dioxide
  • Ammonia
  • Urea
  • Leucine
  • Glucose
  • Nitrogen
  • Glycine