title: Differential loss of fat and lean mass in the morbidly obese after bariatric surgery.
abstract: BACKGROUND
  Bariatric surgery has become a common treatment for morbid obesity. The relative changes in body tissue that comprise the substantial weight loss over time are not completely understood.
  
  
  METHODS
  We evaluated the differential rates of fat and lean tissue losses in morbidly obese patients who underwent Roux-en-Y gastric bypass surgery. Body composition was assessed using whole-body dual energy X-ray absorptiometry (DXA) performed at two timepoints in the postoperative period. Patients were stratified by the tertile of rapidity of weight loss expressed as percent reduction in body mass index per month.
  
  
  RESULTS
  Thirty two patients (25 women, 7 men) with a mean age of 46.7 +/- 10.4 years and an average initial body weight of 141.4 +/- 29.4 kg experienced a 52.3 +/- 16.6 kg (36.5 +/- 5.5%) weight loss over 13.9 +/- 6.0 months. The incremental rates of lean body mass loss by tertiles were 0.3 +/- 0.6, 0.5 +/- 0.2, and 1.0 +/- 0.8 kg/month (P = 0.02), whereas the rates of fat loss were 1.2 +/- 0.9, 1.8 +/- 0.4, and 2.9 +/- 1.0 kg/month (P = 0.0001). The ratios for lean to fat loss among the respective tertiles were 1:4.0, 1:3.6, and 1:3.0. The correlation between rates of lean and fat mass loss was r = 0.37 (P = 0.04). Only three of the 32 patients (9.4%) patients maintained or gained lean mass following Roux-en-Y gastric bypass surgery.
  
  
  CONCLUSIONS
  After bariatric surgery, those patients losing weight at the greatest rate appear to have accelerated losses of both lean and fat mass. Few patients maintain lean body mass after bariatric surgery, despite self-reported participation in conventional exercise programs. These data suggest the need for more aggressive interventions to preserve lean body mass during the weight loss phase after Roux-en-Y gastric bypass surgery.
authors.affiliation: Department of Internal Medicine, Division of Cardiology, William Beaumont Hospital, Royal Oak, Michigan 48073, USA. KZalesin@beaumont.edu
authors.forename: Kerstyn C
authors.initials: KC
authors.lastname: Zalesin
authors.forename: Barry A
authors.initials: BA
authors.lastname: Franklin
authors.forename: Martin A
authors.initials: MA
authors.lastname: Lillystone
authors.forename: Tania
authors.initials: T
authors.lastname: Shamoun
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Krause
authors.forename: David L
authors.initials: DL
authors.lastname: Chengelis
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Mucci
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Shaheen
authors.forename: Peter A
authors.initials: PA
authors.lastname: McCullough
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000273:Adipose Tissue; D000328:Adult; D050110:Bariatric Surgery / Q000379:methods*; D001823:Body Composition; D015992:Body Mass Index; D001835:Body Weight; D005260:Female; D015390:Gastric Bypass / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000628:therapy*; D012189:Retrospective Studies; D015431:Weight Loss