title: Advantages of percent weight loss as a method of reporting weight loss after Roux-en-Y gastric bypass.
abstract: OBJECTIVE
  Although Roux-en-Y gastric bypass (RYGB) is an effective treatment for severe obesity, weight loss (WL) after this operation is highly variable. Accurate predictors of outcome would thus be useful in identifying those patients who would most benefit from this invasive therapy. WL has been characterized using several different metrics, including the number of BMI units lost (ΔBMI), percent baseline WL (%WL), and percent excess body WL (%EBWL). To identify clinically relevant predictors most sensitively, it is necessary to avoid confounding by other factors, including preoperative BMI (pBMI), the strongest known predictor of RYGB-induced WL.
  
  
  METHODS
  To determine the WL measure least associated with pBMI, outcomes of 846 patients undergoing RYGB were analyzed.
  
  
  RESULTS
  Patients in this cohort had an average pBMI of 50.0 kg/m(2) at baseline. At weight nadir, they lost an average 19.4 kg/m(2), 38.7% WL, and 81.2% EBWL. pBMI was strongly and positively associated with ΔBMI at both 1 year (r = 0.56, P = 4.7 × 10(-51)) and nadir (r = 0.58, P = 2.8 × 10(-77)) and strongly but negatively associated with %EBWL at 1 year (r = -0.52, P = 3.8 × 10(-44)) and nadir (r = -0.45, P = 7.2×10(-43)). In contrast, pBMI was not significantly associated with %WL at 1 year (r = 0.04, P = 0.33) and only weakly associated at nadir (r = 0.13, P = 0.0002).
  
  
  CONCLUSIONS
  Of the metrics examined, %WL is the parameter describing WL after RYGB least influenced by pBMI. It thus improves comparison of WL outcomes across studies of patients undergoing surgery and facilitates the most sensitive identification of novel predictors of surgery-induced WL. We therefore is recommend that %WL be adopted more broadly in reporting weight loss after RYGB.
authors.affiliation: Obesity, Metabolism & Nutrition Institute and Gastrointestinal Unit, Massachusetts General Hospital, Boston, Massachusetts, USA.
authors.forename: Ida J
authors.initials: IJ
authors.lastname: Hatoum
authors.forename: Lee M
authors.initials: LM
authors.lastname: Kaplan
mesh_terms: D000328:Adult; D000713:Anastomosis, Roux-en-Y; D015992:Body Mass Index; D015331:Cohort Studies; D023381:Endpoint Determination; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000601:surgery*; D011184:Postoperative Period; D057234:Preoperative Period; D016896:Treatment Outcome; D015431:Weight Loss