title: The 24-h kinetics of leucine oxidation in healthy adults receiving a generous leucine intake via three discrete meals.
abstract: The significance of meal size and frequency for the 24-h leucine tracer-balance technique was examined. Continuous measurements of leucine oxidation throughout a 24-h d were performed in six healthy, young adults who were given a weight-maintaining diet (188 kJ.kg-1.d-1; 1 g protein.kg-1.d-1) for 6 d followed by primed, continuous intravenous infusions of L-[1-13C]leucine and [15N-15N]urea. The 24-h study was started at 1800 on day 6 and three equal discrete meals were given at 2000, 0600, and 1200. Leucine oxidation was assessed from plasma [13C]alpha-ketoisocaproate enrichment and 13CO2 excretion. The mean (+/- SD) leucine oxidation after each meal (over 6 h) was not significantly different (P > 0.5) among the three discrete meals: 20.0 +/- 3.9, 20.2 +/- 1.9, and 20.3 +/- 2.4 mg.kg-1.d-1 for the meals given at 2000, 0600, and 1200, respectively. Twenty-four-hour leucine oxidation was 75.0 +/- 7.8 mg.kg-1.d-1 for a leucine dietary intake of 80 mg.kg-1.d-1 (and approximately 9.7 mg tracer.kg-1.d-1). The 24-h pattern in leucine oxidation was paralleled by plasma leucine concentrations. Further, leucine oxidation and urea excretion predicted relatively similar values for 24-h protein oxidation. These data are compared with results from our similar previous studies using a multiple-small-meal feeding protocol.
authors.affiliation: Laboratory of Human Nutrition, School of Science, Massachusetts Institute of Technology, Cambridge 02142, USA.
authors.forename: A E
authors.initials: AE
authors.lastname: el-Khoury
authors.forename: M
authors.initials: M
authors.lastname: Sánchez
authors.forename: N K
authors.initials: NK
authors.lastname: Fukagawa
authors.forename: R E
authors.initials: RE
authors.lastname: Gleason
authors.forename: R H
authors.initials: RH
authors.lastname: Tsay
authors.forename: V R
authors.initials: VR
authors.lastname: Young
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000378:metabolism; D002940:Circadian Rhythm; D004032:Diet; D004435:Eating; D005247:Feeding Behavior; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000008:administration & dosage* / Q000097:blood / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism / Q000652:urine; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D011506:Proteins / Q000378:metabolism; D012016:Reference Values
chemical_list: D011506:Proteins; D002245:Carbon Dioxide; D007930:Leucine; D009584:Nitrogen