title: How adaptations of substrate utilization regulate body composition.
abstract: OBJECTIVE
  To elucidate the mathematical relationship between longitudinal changes of body composition and the adaptations of substrate utilization required to produce those changes.
  
  
  METHODS
  We developed a simple mathematical model of macronutrient balance. By using an empirical relationship describing lean body mass as a function of fat mass, we derived a mathematical expression for how substrate utilization adapts to changes of diet, energy expenditure and body fat such that energy imbalances produced the required changes of body composition.
  
  
  RESULTS
  The general properties of our model implied that short-term changes of dietary fat alone had little impact on either fat or non-fat oxidation rates, in agreement with indirect calorimetry data. In contrast, changes of non-fat intake caused robust adaptations of both fat and non-fat oxidation rates. Without fitting any model parameters, the predicted body composition changes and oxidation rates agreed with experimental studies of overfeeding and underfeeding when the measured food intake, energy expenditure and initial body composition were used as model inputs.
  
  
  CONCLUSIONS
  This is the first report to define the quantitative connection between longitudinal changes of body composition and the required relationship between substrate utilization, diet, energy expenditure and body fat mass. The mathematical model predictions are in good agreement with experimental data and provide the basis for future study of how changes of substrate utilization impact body composition regulation.
authors.affiliation: Laboratory of Biological Modeling, National Institute of Diabetes & Digestive & Kidney Diseases, National Institutes of Health, Bethesda, MD, USA. kevinh@niddk.nih.gov
authors.forename: K D
authors.initials: KD
authors.lastname: Hall
authors.forename: H L
authors.initials: HL
authors.lastname: Bain
authors.forename: C C
authors.initials: CC
authors.lastname: Chow
mesh_terms: D000328:Adult; D001823:Body Composition; D004734:Energy Metabolism; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D009765:Obesity / Q000378:metabolism*; D011237:Predictive Value of Tests; D015430:Weight Gain / Q000502:physiology*; D015431:Weight Loss / Q000502:physiology*