title: Effect of calorie restriction on resting metabolic rate and spontaneous physical activity.
abstract: OBJECTIVE
  It is unclear if resting metabolic rate (RMR) and spontaneous physical activity (SPA) decrease in weight-reduced non-obese participants. Additionally, it is unknown if changes in SPA, measured in a respiratory chamber, reflect changes in free-living physical activity level (PAL).
  
  
  METHODS
  Participants (N = 48) were randomized into 4 groups for 6 months: calorie restriction (CR, 25% restriction), CR plus structured exercise (CR+EX, 12.5% restriction plus 12.5% increased energy expenditure via exercise), low-calorie diet (LCD, 890 kcal/d supplement diet until 15% weight loss, then weight maintenance), and control (weight maintenance). Measurements were collected at baseline, Month 3, and Month 6. Body composition and RMR were measured by DXA and indirect calorimetry, respectively. Two measures of SPA were collected in a respiratory chamber (percent of time active and kcal/d). Free-living PAL (PAL = total daily energy expenditure by doubly labeled water/RMR) was also measured. Regression equations at baseline were used to adjust RMR for fat-free mass and SPA (kcal/d) for body weight.
  
  
  RESULTS
  Adjusted RMR decreased at Month 3 in the CR group and at Month 6 in the CR+EX and LCD groups. Neither measure of SPA decreased significantly in any group. PAL decreased at Month 3 in the CR and LCD groups, but not in the CR+EX group, who engaged in structured exercise. Changes in SPA in the chamber and free-living PAL were not related.
  
  
  CONCLUSIONS
  Body weight is defended in non-obese participants during modest caloric restriction, evidenced by metabolic adaptation of RMR and reduced energy expenditure through physical activity.
authors.affiliation: Department of Health Psychology, Pennington Biomedical Research Center, 6400 Perkins Rd., Baton Rouge, LA 70808, USA. martinck@pbrc.edu
authors.forename: Corby K
authors.initials: CK
authors.lastname: Martin
authors.forename: Leonie K
authors.initials: LK
authors.lastname: Heilbronn
authors.forename: Lilian
authors.initials: L
authors.lastname: de Jonge
authors.forename: James P
authors.initials: JP
authors.lastname: DeLany
authors.forename: Julia
authors.initials: J
authors.lastname: Volaufova
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Anton
authors.forename: Leanne M
authors.initials: LM
authors.lastname: Redman
authors.forename: Steven R
authors.initials: SR
authors.lastname: Smith
authors.forename: Eric
authors.initials: E
authors.lastname: Ravussin
mesh_terms: D000328:Adult; D001481:Basal Metabolism / Q000502:physiology*; D015992:Body Mass Index; D001835:Body Weight / Q000502:physiology; D031204:Caloric Restriction; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D050177:Overweight / Q000178:diet therapy / Q000503:physiopathology; D015431:Weight Loss / Q000502:physiology