title: New insights into the methodological issues of the indicator amino acid oxidation method in preterm neonates.
abstract: BACKGROUND
  We determined the effect of adaptation to the study diet on oxidation of the indicator amino acid and the required tracer washout time in preterms.
  
  
  METHODS
  Subjects received a study diet for 6 d that entailed a 50% reduction in leucine. Tracer studies using enterally infused [(13)C]bicarbonate and [1-(13)C]phenylalanine were performed on days 1, 2, 4, and 6. Breath samples containing (13)CO2 were collected during steady state and measured by infrared spectrometric analysis, and the fraction of (13)CO2 recovery from (13)C oxidation (F(13)CO2) was calculated.
  
  
  RESULTS
  Preterm infants (n = 11, birth weight 1.9 ± 0.1 kg, gestational age 32.6 ± 1.5 wk) received 166 mg/kg/d of leucine. Baseline enrichment changed significantly at day 1 of the study diet. F(13)CO2 did not change significantly between days 2 and 4 but was significantly lower at day 6. The tracer washout time was determined to be 7.5 h using a biphasic regression analysis.
  
  
  CONCLUSIONS
  One day of adaptation to a new diet is necessary to adapt to the (13)C enrichment of the study formula before starting infant requirement studies. Adaptation for a period of 5 d results in a protein-sparing response. The minimal time between two studies within the same subject is 7.5 h.
authors: Division of Neonatology, Department of Pediatrics, Erasmus Medical Center, Sophia Children's Hospital Rotterdam, Rotterdam, The Netherlands.
authors: Femke
authors: F
authors: de Groof
authors: Lisha
authors: L
authors: Huang
authors: Jos W R
authors: JW
authors: Twisk
authors: Gardi J
authors: GJ
authors: Voortman
authors: Waheeda
authors: W
authors: Joemai
authors: Carmen H
authors: CH
authors: Hau
authors: Henk
authors: H
authors: Schierbeek
authors: Chao
authors: C
authors: Chen
authors: Ying
authors: Y
authors: Huang
authors: Johannes B
authors: JB
authors: van Goudoever
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D010084:Oxidation-Reduction
chemical_list: D000596:Amino Acids