title: Metabolic and behavioral compensations in response to caloric restriction: implications for the maintenance of weight loss.
abstract: BACKGROUND
  Metabolic and behavioral adaptations to caloric restriction (CR) in free-living conditions have not yet been objectively measured.
  
  
  RESULTS
  Forty-eight (36.8+/-1.0 y), overweight (BMI 27.8+/-0.7 kg/m(2)) participants were randomized to four groups for 6-months;
  
  
  METHODS
  energy intake at 100% of energy requirements; CR: 25% calorie restriction; CR+EX: 12.5% CR plus 12.5% increase in energy expenditure by structured exercise; LCD: low calorie diet (890 kcal/d) until 15% weight reduction followed by weight maintenance. Body composition (DXA) and total daily energy expenditure (TDEE) over 14-days by doubly labeled water (DLW) and activity related energy activity (AREE) were measured after 3 (M3) and 6 (M6) months of intervention. Weight changes at M6 were -1.0+/-1.1% (CONTROL), -10.4+/-0.9% (CR), -10.0+/-0.8% (CR+EX) and -13.9+/-0.8% (LCD). At M3, absolute TDEE was significantly reduced in CR (-454+/-76 kcal/d) and LCD (-633+/-66 kcal/d) but not in CR+EX or controls. At M6 the reduction in TDEE remained lower than baseline in CR (-316+/-118 kcal/d) and LCD (-389+/-124 kcal/d) but reached significance only when CR and LCD were combined (-351+/-83 kcal/d). In response to caloric restriction (CR/LCD combined), TDEE adjusted for body composition, was significantly lower by -431+/-51 and -240+/-83 kcal/d at M3 and M6, respectively, indicating a metabolic adaptation. Likewise, physical activity (TDEE adjusted for sleeping metabolic rate) was significantly reduced from baseline at both time points. For control and CR+EX, adjusted TDEE (body composition or sleeping metabolic rate) was not changed at either M3 or M6.
  
  
  CONCLUSIONS
  For the first time we show that in free-living conditions, CR results in a metabolic adaptation and a behavioral adaptation with decreased physical activity levels. These data also suggest potential mechanisms by which CR causes large inter-individual variability in the rates of weight loss and how exercise may influence weight loss and weight loss maintenance.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT00099151.
authors.affiliation: Pennington Biomedical Research Center, Baton Rouge, Louisiana, United States of America.
authors.forename: Leanne M
authors.initials: LM
authors.lastname: Redman
authors.forename: Leonie K
authors.initials: LK
authors.lastname: Heilbronn
authors.forename: Corby K
authors.initials: CK
authors.lastname: Martin
authors.forename: Lilian
authors.initials: L
authors.lastname: de Jonge
authors.forename: Donald A
authors.initials: DA
authors.lastname: Williamson
authors.forename: James P
authors.initials: JP
authors.lastname: Delany
authors.forename: Eric
authors.initials: E
authors.lastname: Ravussin
mesh_terms: D000328:Adult; D032763:Behavior Control / Q000523:psychology; D001823:Body Composition / Q000502:physiology; D015992:Body Mass Index; D031204:Caloric Restriction; D002149:Energy Intake / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015431:Weight Loss / Q000502:physiology*