Study on weight loss outcomes after bariatric surgery to determine a metric least influenced by preoperative BMI

Percentage excess weight loss (%EWL) and percentage total weight loss (%TWL) are used for reporting outcomes after bariatric surgery. However, they are not ideal for comparing outcomes on populations of varied initial body mass index (BMI). This study aimed to validate a recently introduced metric - percentage alterable weight loss (%AWL), after laparoscopic sleeve gastrectomy (LSG) and Roux-en-Y gastric bypass (LRYGB).

Analysis of weight data of all patients who had undergone LSG and LRYGB until the end of the year 2021. Outcomes for both procedures were analyzed separately. The patients were divided into quartile subgroups Q1 (lowest BMI) to Q4 (highest BMI) and weight loss up to 5 years postoperatively was compared using %EWL, %TWL and %AWL metrics. An intermediary metric was also tested for its effect on the weight loss patterns for both procedures.

The cohort included 1020 LSG and 322 LRYGB patients, with initial mean BMI of 43.5 ± 7.5 and 41.9 ± 8.3 kg/m², respectively. %EWL significantly favors lower BMI subgroups for both procedures. %TWL is ideal for comparing weight loss during the first 6 months but it then favors higher BMI subgroups beyond 6 months. %AWL with reference BMI of 13 kg/m² seems the best metric for medium-term comparison of weight loss for LRYGB and an intermediary metric based on BMI 8 kg/m² provides the best fit for medium-term comparison for LSG.

%TWL is least influenced by initial BMI during short-term follow-up after LSG and LRYGB. For medium-term comparison, %AWL is best suited for LRYGB while an intermediary metric is found to provide the best fit for LSG.