title: Higher Daily Energy Expenditure and Respiratory Quotient, Rather Than Fat-Free Mass, Independently Determine Greater ad Libitum Overeating.
abstract: BACKGROUND
  Body fat-free mass (FFM), energy expenditure (EE), and respiratory quotient (RQ) are known predictors of daily food intake. Because FFM largely determines EE, it is unclear whether body composition per se or the underlying metabolism drives dietary intake.
  
  
  OBJECTIVE
  The objective of the study was to test whether 24-hour measures of EE and RQ and their components influence ad libitum food intake independently of FFM.
  
  
  METHODS
  One hundred seven healthy individuals (62 males/45 females, 84 Native Americans/23 whites; age 33 ± 8 y; body mass index 33 ± 8 kg/m(2); body fat 31% ± 8%) had 24-hour measures of EE in a whole-room indirect calorimeter during energy balance, followed by 3 days of ad libitum food intake using computerized vending machine systems. Body composition was estimated by dual-energy x-ray absorptiometry.
  
  
  METHODS
  FFM, 24-hour EE, RQ, spontaneous physical activity, sleeping EE (sleeping metabolic rate), awake and fed thermogenesis, and ad libitum food intake (INTAKE) were measured.
  
  
  RESULTS
  Higher 24-hour RQ (P < .001, partial R(2) = 16%) and EE (P = .01, partial R(2) = 7%), but not FFM (P = .65), were independent predictors of INTAKE. Mediation analysis demonstrated that 24-hour EE is responsible for 80% of the FFM effect on INTAKE (44.5 ± 16.9 kcal ingested per kilogram of FFM, P= .01), whereas the unique effect due to solely FFM was negligible (10.6 ± 23.2, P = .65). Spontaneous physical activity (r = 0.33, P = .001), but not sleeping metabolic rate (P = .71), positively predicted INTAKE, whereas higher awake and fed thermogenesis determined greater INTAKE only in subjects with a body mass index of 29 kg/m(2) or less (r = 0.44, P = .01).
  
  
  CONCLUSIONS
  EE and RQ, rather than FFM, independently determine INTAKE, suggesting that competitive energy-sensing mechanisms driven by the preferential macronutrient oxidation and total energy demands may regulate food intake.
authors.affiliation: Obesity and Diabetes Clinical Research Section (P.P., M.S.T., J.K., S.B.V.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona 85016; and Obesity Research Center (P.P.), Endocrinology Unit, University Hospital of Pisa, Pisa, Italy 56124.
authors.forename: Paolo
authors.initials: P
authors.lastname: Piaggi
authors.affiliation: Obesity and Diabetes Clinical Research Section (P.P., M.S.T., J.K., S.B.V.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona 85016; and Obesity Research Center (P.P.), Endocrinology Unit, University Hospital of Pisa, Pisa, Italy 56124.
authors.forename: Marie S
authors.initials: MS
authors.lastname: Thearle
authors.affiliation: Obesity and Diabetes Clinical Research Section (P.P., M.S.T., J.K., S.B.V.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona 85016; and Obesity Research Center (P.P.), Endocrinology Unit, University Hospital of Pisa, Pisa, Italy 56124.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Krakoff
authors.affiliation: Obesity and Diabetes Clinical Research Section (P.P., M.S.T., J.K., S.B.V.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona 85016; and Obesity Research Center (P.P.), Endocrinology Unit, University Hospital of Pisa, Pisa, Italy 56124.
authors.forename: Susanne B
authors.initials: SB
authors.lastname: Votruba
mesh_terms: D000273:Adipose Tissue / Q000502:physiology; D000328:Adult; D001823:Body Composition / Q000502:physiology*; D001835:Body Weight / Q000502:physiology*; D002153:Calorimetry, Indirect; D002940:Circadian Rhythm; D004435:Eating / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D006963:Hyperphagia / Q000175:diagnosis / Q000209:etiology* / Q000378:metabolism; D008297:Male; D010084:Oxidation-Reduction; D012119:Respiration; D055815:Young Adult