1- and 2-year outcomes and predictors of weight loss after gastric sleeve to Roux-en-Y gastric bypass conversion: a retrospective cohort study.

Background: Sleeve gastrectomy to Roux-en-Y bypass conversion is a commonly performed procedure, yet data are limited on outcomes and their predictors. The purpose of this study is to characterize the long-term outcomes of patients after sleeve-to-bypass conversion and identify predictors of post-conversion outcomes.

Methods: We performed a retrospective cohort study of patients who underwent sleeve-to-bypass conversion for obesity across four hospitals from 06/2017 to 04/2023. Predictors of the below-average percent excess weight loss (%EWL; relative to pre-conversion weight) at 1 and 2 years following conversion were identified using multivariate logistic regression models adjusting for comorbidities, demographics, and neighborhood socioeconomic status.

Results: 150 Patients undergoing sleeve-to-bypass conversion were identified. 99 had 1-year data and 63 had 2-year data. Mean %EWL at 1- and 2-years following conversion were 40.2% and 37.4%, respectively. EWL > 40% after sleeve gastrectomy was an independent predictor of the below-average %EWL 1-year post-conversion (OR 10.0, 95% CI 2.2-63.0, p < 0.01), and BMI > 40 kg/m at the time of conversion was an independent predictor of both 1- and 2-year below-average %EWL post-conversion (p = 0.01 and 0.05, respectively). Insignificant predictors of the below-average %EWL after conversion included: weight regain after sleeve, time between sleeve and conversion, alimentary limb length, and any bariatric surgery prior to sleeve gastrectomy.

Conclusion: Patients should be counseled that the typical expected %EWL for sleeve-to-bypass conversion is less than the 50% EWL benchmark of success for index bariatric operations. The main predictors of a suboptimal conversion outcome are > 40% EWL after sleeve or > 40 BMI kg/m at the time of conversion. Most variables in our analysis were not predictors of post-conversion %EWL, including weight regain between sleeve and conversion, alimentary limb length, and time interval between procedures, which suggests that these factors should not play a large role when considering sleeve-to-bypass conversion.