Effect of preoperative body mass index on weight loss after obesity surgery

Previous studies suggest that individuals with body mass index (BMI) above versus below 60 kg/m(2) attain lower percentage of excess weight loss (%EWL) after bariatric surgery. The objectives of this study were to (1) test whether conclusions drawn about the effect of preoperative BMI on postoperative weight loss depend on the outcome measure, (2) test for evidence of a threshold effect at BMI = 60 kg/m(2), and (3) test the effect from surgery to 12-month follow-up, relative to 12- to 36-month follow-up.

Retrospective analyses of participants grouped according to preoperative BMI: 35-39.9 (n = 232); 40-49.9 (n = 1166); 50-59.9 (n = 429);≥60 (n = 166).

As anticipated, individuals with higher versus lower preoperative BMI had greater total weight loss but lower %EWL at all postoperative time points (all, P<.0005). However, these individuals also had lower percentage of initial weight loss (%IWL) at all time points beyond 1 month postsurgery (all, P<.0005). From 12- to 36-months, individuals with BMI 35-39.9 had 3.2±14.3 %IWL (P<.0001); 40-49.9 had 1.0±8.9 %IWL (P<.0005); 50-59.9 had-2.4±10.0 %IWL (P<.0005); and≥60 had-3.6±11.5 %IWL (P<.0005). Overall F3,1989 = 20.2, P< .0005.

Conclusions drawn about the effect of preoperative BMI may depend on the outcome measure. A dosage effect of preoperative BMI was apparent, with heavier individuals showing lower percentages of initial and excess weight loss, regardless of BMI above or below 60 kg/m(2). Finally, this effect was particularly apparent after the initial 12-month rapid weight loss phase, when less obese (BMI<50) individuals continued losing weight, while heavier individuals (BMI≥50) regained significant weight.