title: Metabolic slowing with massive weight loss despite preservation of fat-free mass.
abstract: BACKGROUND
  An important goal during weight loss is to maximize fat loss while preserving metabolically active fat-free mass (FFM). Massive weight loss typically results in substantial loss of FFM potentially slowing metabolic rate.
  
  
  OBJECTIVE
  Our objective was to determine whether a weight loss program consisting of diet restriction and vigorous exercise helped to preserve FFM and maintain resting metabolic rate (RMR).
  
  
  METHODS
  We measured body composition by dual-energy x-ray absorptiometry, RMR by indirect calorimetry, and total energy expenditure by doubly labeled water at baseline (n = 16), wk 6 (n = 11), and wk 30 (n = 16).
  
  
  RESULTS
  At baseline, participants were severely obese (× ± SD; body mass index 49.4 ± 9.4 kg/m(2)) with 49 ± 5% body fat. At wk 30, more than one third of initial body weight was lost (-38 ± 9%) and consisted of 17 ± 8% from FFM and 83 ± 8% from fat. RMR declined out of proportion to the decrease in body mass, demonstrating a substantial metabolic adaptation (-244 ± 231 and -504 ± 171 kcal/d at wk 6 and 30, respectively, P < 0.01). Energy expenditure attributed to physical activity increased by 10.2 ± 5.1 kcal/kg.d at wk 6 and 6.0 ± 4.1 kcal/kg.d at wk 30 (P < 0.001 vs. zero).
  
  
  CONCLUSIONS
  Despite relative preservation of FFM, exercise did not prevent dramatic slowing of resting metabolism out of proportion to weight loss. This metabolic adaptation may persist during weight maintenance and predispose to weight regain unless high levels of physical activity or caloric restriction are maintained.
authors.affiliation: Skeletal Muscle Physiology Laboratory, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 12A South Drive, Room 4007, Bethesda, Maryland 20892, USA. ke
authors.forename: Darcy L
authors.initials: DL
authors.lastname: Johannsen
authors.forename: Nicolas D
authors.initials: ND
authors.lastname: Knuth
authors.forename: Robert
authors.initials: R
authors.lastname: Huizenga
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Rood
authors.forename: Eric
authors.initials: E
authors.lastname: Ravussin
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Hall
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000473:pathology; D000328:Adult; D001481:Basal Metabolism / Q000502:physiology*; D001823:Body Composition / Q000502:physiology*; D001835:Body Weight / Q000502:physiology*; D003131:Combined Modality Therapy; D004038:Diet, Reducing; D015536:Down-Regulation / Q000502:physiology; D005081:Exercise Therapy; D005260:Female; D006801:Humans; D008297:Male; D008659:Metabolic Diseases / Q000150:complications; D008875:Middle Aged; D009767:Obesity, Morbid / Q000378:metabolism / Q000534:rehabilitation / Q000628:therapy; D015430:Weight Gain / Q000502:physiology; D015431:Weight Loss / Q000502:physiology*; D061217:Weight Reduction Programs / Q000379:methods; D055815:Young Adult