title: Moderate exercise attenuates the loss of skeletal muscle mass that occurs with intentional caloric restriction-induced weight loss in older, overweight to obese adults.
abstract: BACKGROUND
  Aging is associated with a loss of muscle mass and increased body fat. The effects of diet-induced weight loss on muscle mass in older adults are not clear.
  
  
  OBJECTIVE
  This study examined the effects of diet-induced weight loss, alone and in combination with moderate aerobic exercise, on skeletal muscle mass in older adults.
  
  
  METHODS
  Twenty-nine overweight to obese (body mass index = 31.8 +/- 3.3 kg/m(2)) older (67.2 +/- 4.2 years) men (n = 13) and women (n = 16) completed a 4-month intervention consisting of diet-induced weight loss alone (WL; n = 11) or with exercise (WL/EX; n = 18). The WL intervention consisted of a low-fat, 500-1,000 kcal/d caloric restriction. The WL/EX intervention included the WL intervention with the addition of aerobic exercise, moderate-intensity walking, three to five times per week for 35-45 minutes per session. Whole-body dual-energy x-ray absorptiometry, thigh computed tomography (CT), and percutaneous muscle biopsy were performed to assess changes in skeletal muscle mass at the whole-body, regional, and cellular level, respectively.
  
  
  RESULTS
  Mixed analysis of variance demonstrated that both groups had similar decreases in bodyweight (WL, -9.2% +/- 1.0%; WL/EX, -9.1% +/- 1.0%) and whole-body fat mass (WL, -16.5%, WL/EX, -20.7%). However, whole-body fat-free mass decreased significantly (p < .05) in WL (-4.3% +/- 1.2%) but not in WL/EX (-1.1% +/- 1.0%). Thigh muscle cross-sectional area by CT decreased in both groups (WL, -5.2% +/- 1.1%; WL/EX, -3.0% +/- 1.0%) and was not statistically different between groups. Type I muscle fiber area decreased in WL (-19.2% +/- 7.9%, p = .01) but remained unchanged in WL/EX (3.4% +/- 7.5%). Similar patterns were observed in type II fibers (WL, -16.6% +/- 4.0%; WL/EX, -0.2% +/- 6.5%).
  
  
  CONCLUSIONS
  Diet-induced weight loss significantly decreased muscle mass in older adults. However, the addition of moderate aerobic exercise to intentional weight loss attenuated the loss of muscle mass.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Medicine, University of Pittsburgh School of Medicine, Pennsylvania 15213, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Chomentowski
authors.forename: John J
authors.initials: JJ
authors.lastname: Dubé
authors.forename: Francesca
authors.initials: F
authors.lastname: Amati
authors.forename: Maja
authors.initials: M
authors.lastname: Stefanovic-Racic
authors.forename: Shanjian
authors.initials: S
authors.lastname: Zhu
authors.forename: Frederico G S
authors.initials: FG
authors.lastname: Toledo
authors.forename: Bret H
authors.initials: BH
authors.lastname: Goodpaster
mesh_terms: D000368:Aged; D015992:Body Mass Index; D031204:Caloric Restriction; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal; D009765:Obesity / Q000178:diet therapy*; D015431:Weight Loss