Comparison between total weight loss and other metrics after bariatric surgery using a multilevel mixed-effects linear regression model

Background Several tools are used to assess postoperative weight loss after bariatric surgery, including the percentage of excess body weight loss (%EWL), percentage of total weight loss (%TWL), and percentage of excess body mass index (BMI) loss (%EBMIL). A repeated series of measurements should be considered to assess weight loss as accurately as possible. This study aimed to test weight loss metrics. Methods Data were obtained from a prospective database of patients with obesity who underwent laparoscopic Roux-en-Y gastric bypass (LRYGB) or laparoscopic sleeve gastrectomy (LSG) between 2016 and 2017 in a French tertiary referral bariatric center. A multilevel mixed-effects linear regression model with repeated measures was used to analyze repeated weight measurements over time. Results A total of 435 patients underwent LRYGB ( n = 266) or LSG ( n = 169). At 2 years, the average %EWL, %EBMIL, and %TWL were 56.8%, 61.3%, and 26.6%, respectively. Patients who underwent LSG experienced lower weight loss ( β : − 4233 in %TWL model, β : − 6437 in %EWL model, and β : − 6989 in %EBMIL model) than those who underwent LRYGB. In multivariate mixed analysis, preoperative BMI was not significantly associated with %TWL at 2 years ( β , − 0.09 [− 0.22–0.03] p = 0.1). Preoperative BMI was negatively associated with both %EWL ( β , − 1.61 [− 1.84–− 1.38] p