title: Ingested fat oxidation contributes 8% of 24-h total energy expenditure in moderately obese subjects.
abstract: The role of ingested fat in the etiology of obesity is controversial. The aims of this study were to determine the contributions of ingested fat oxidation to: 1) 24-h total energy expenditure (TEE), and 2) substrate oxidation during acute stationary cycle exercises in adult humans. Healthy, moderately obese (n = 18; BMI = 31 +/- 1 kg/m2) subjects (8 men; 10 women) were each studied in a whole-room calorimeter for 24 h. They were fed mixed meals (55, 30, and 15% as energy from carbohydrate, fat and protein, respectively) to maintain energy balance. Each subject performed 1255-kJ cycle exercises at 50% VO2max in the calorimeter. Study test meal fat was labeled with carbon-13 (13C). Ingested fat oxidation was estimated from breath 13CO2 excretion and the subject's chamber CO2 production. Total fat and carbohydrate oxidations were estimated from nonprotein respiratory quotient (NP-RQ) values. Endogenous fat oxidation was estimated as the difference between total fat and ingested fat oxidations. TEE was estimated from gas exchanges; 28 +/- 3% of ingested fat was oxidized and it provided 8 +/- 1% of 24-h TEE. During cycle exercises, ingested fat provided 50% of total fat oxidized and 13.0 +/- 2% of energy expended. Endogenous fat oxidation contributed 10.4 +/- 3% of energy expenditure during cycle exercises. This study extended to 24-h observations of previous studies that lasted 6-9 h on ingested fat oxidation in humans. Understanding the factors that promote ingested fat oxidation could lead to more effective obesity intervention programs.
authors.affiliation: University of Colorado Health Sciences Center, Denver, CO 80262, USA. bakary.sonko@uchsc.edu
authors.forename: Bakary J
authors.initials: BJ
authors.lastname: Sonko
authors.forename: Paul V
authors.initials: PV
authors.lastname: Fennessey
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Donnelly
authors.forename: Daniel
authors.initials: D
authors.lastname: Bessesen
authors.forename: Teresa A
authors.initials: TA
authors.lastname: Sharp
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: Jacobsen
authors.forename: Richard H
authors.initials: RH
authors.lastname: Jones
authors.forename: James O
authors.initials: JO
authors.lastname: Hill
mesh_terms: D000328:Adult; D001642:Bicycling; D001823:Body Composition; D002245:Carbon Dioxide; D002940:Circadian Rhythm; D004041:Dietary Fats / Q000378:metabolism*; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000378:metabolism*; D010084:Oxidation-Reduction; D011659:Pulmonary Gas Exchange; D012119:Respiration; D012720:Severity of Illness Index
chemical_list: D004041:Dietary Fats; D002245:Carbon Dioxide