title: Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men.
abstract: BACKGROUND
  The carbohydrate-insulin model of obesity posits that habitual consumption of a high-carbohydrate diet sequesters fat within adipose tissue because of hyperinsulinemia and results in adaptive suppression of energy expenditure (EE). Therefore, isocaloric exchange of dietary carbohydrate for fat is predicted to result in increased EE, increased fat oxidation, and loss of body fat. In contrast, a more conventional view that "a calorie is a calorie" predicts that isocaloric variations in dietary carbohydrate and fat will have no physiologically important effects on EE or body fat.
  
  
  OBJECTIVE
  We investigated whether an isocaloric low-carbohydrate ketogenic diet (KD) is associated with changes in EE, respiratory quotient (RQ), and body composition.
  
  
  METHODS
  Seventeen overweight or obese men were admitted to metabolic wards, where they consumed a high-carbohydrate baseline diet (BD) for 4 wk followed by 4 wk of an isocaloric KD with clamped protein. Subjects spent 2 consecutive days each week residing in metabolic chambers to measure changes in EE (EEchamber), sleeping EE (SEE), and RQ. Body composition changes were measured by dual-energy X-ray absorptiometry. Average EE during the final 2 wk of the BD and KD periods was measured by doubly labeled water (EEDLW).
  
  
  RESULTS
  Subjects lost weight and body fat throughout the study corresponding to an overall negative energy balance of ∼300 kcal/d. Compared with BD, the KD coincided with increased EEchamber (57 ± 13 kcal/d, P = 0.0004) and SEE (89 ± 14 kcal/d, P < 0.0001) and decreased RQ (-0.111 ± 0.003, P < 0.0001). EEDLW increased by 151 ± 63 kcal/d (P = 0.03). Body fat loss slowed during the KD and coincided with increased protein utilization and loss of fat-free mass.
  
  
  CONCLUSIONS
  The isocaloric KD was not accompanied by increased body fat loss but was associated with relatively small increases in EE that were near the limits of detection with the use of state-of-the-art technology. This trial was registered at clinicaltrials.gov as NCT01967563.
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD; kevinh@niddk.nih.gov.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Hall
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD;
authors.forename: Kong Y
authors.initials: KY
authors.lastname: Chen
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD;
authors.forename: Juen
authors.initials: J
authors.lastname: Guo
authors.affiliation: Pennington Biomedical Research Center, Baton Rouge, LA;
authors.forename: Yan Y
authors.initials: YY
authors.lastname: Lam
authors.affiliation: Columbia University, New York, NY; and.
authors.forename: Rudolph L
authors.initials: RL
authors.lastname: Leibel
authors.affiliation: Columbia University, New York, NY; and.
authors.forename: Laurel Es
authors.initials: LE
authors.lastname: Mayer
authors.affiliation: National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD;
authors.forename: Marc L
authors.initials: ML
authors.lastname: Reitman
authors.affiliation: Columbia University, New York, NY; and.
authors.forename: Michael
authors.initials: M
authors.lastname: Rosenbaum
authors.affiliation: The Translational Research Institute for Metabolism and Diabetes, Orlando, FL.
authors.forename: Steven R
authors.initials: SR
authors.lastname: Smith
authors.affiliation: Columbia University, New York, NY; and.
authors.forename: B Timothy
authors.initials: BT
authors.lastname: Walsh
authors.affiliation: Pennington Biomedical Research Center, Baton Rouge, LA;
authors.forename: Eric
authors.initials: E
authors.lastname: Ravussin
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000328:Adult; D001823:Body Composition / Q000187:drug effects*; D050528:Diet, Carbohydrate-Restricted; D055423:Diet, Ketogenic; D004040:Dietary Carbohydrates / Q000008:administration & dosage* / Q000378:metabolism / Q000494:pharmacology; D004041:Dietary Fats / Q000008:administration & dosage* / Q000378:metabolism / Q000494:pharmacology; D002149:Energy Intake; D004734:Energy Metabolism / Q000187:drug effects*; D006801:Humans; D008297:Male; D009765:Obesity / Q000178:diet therapy* / Q000378:metabolism; D050177:Overweight; D015431:Weight Loss
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats
keywords: body composition; carbohydrate; energy expenditure; fat; insulin; ketogenic diet; macronutrients