Defining Weight Loss After Bariatric Surgery: a Call for Standardization

Background Some weight regain is expected after bariatric surgery; however, this concept is not well defined. A favorable weight loss response has commonly been defined as 50% excess weight loss (EWL). The medical literature uses %total weight loss (%TWL), which has recently been adopted in some surgical literature. Objective To demonstrate variability in bariatric surgery outcomes based on the definition applied and propose a standardized definition. Methods A retrospective review of patients who underwent bariatric surgery from 2001 to 2016 with >= 1 year follow-up was completed. Several previously proposed definitions of weight regain were analyzed. Results One thousand five hundred seventy-four patients met inclusion criteria. Preoperative mean body mass index (BMI) was 47.6 +/- 6.4 kg/m(2). Increased preoperative BMI was associated with increased mean %TWL at 2 years postoperative (29.3 +/- 9.1% for BMI < 40, vs. 37.5 +/- 9.5% for BMI > 60; P < 0.001). Based on %EWL, 93% of patients experienced >= 50% EWL by 1-2 years, and 61.8% maintained >= 50% EWL through the 10-year follow-up period. Similarly, 97% experienced >= 20% TWL by 1-2 years and 70.3% maintained >= 20% TWL through the 10-year follow-up period. Over 50% of patients maintained their weight based on several proposed definitions through 5 years follow-up. Conclusions A high percentage (> 90%) of patients achieve >= 20% TWL and >= 50% EWL. Increased preoperative BMI was associated with increased %TWL and decreased %EWL at 2 years postoperative. The incidence of weight regain varies depending on the definition. We propose a standardized definition for identifying good responders following bariatric surgery to be >= 20% TWL, as this measure is least influenced by preoperative BMI.