Background

Conversion from LSG to RYGB may be indicated for patients due to insufficient weight loss, weight regain, or GERD. Our aim was to assess weight loss outcomes and factors predictive of improved weight loss in patients undergoing RYGB after LSG, and to create an algorithm to estimate postoperative weight loss in these patients.

Methods

A single-center retrospective review of patients who underwent conversion from LSG to RYGB from 2015 to 2022 was performed, assessing pre- and post-operative weights for each procedure.

Results

130 patients were included (84% female, pre-LSG BMI 49.3 ± 10.2). Post-LSG, patients achieved a maximum %TBWL of 31.2% ([6.6-58.2]±10.1%), %EWL of 56.8%([13.3-97.3]±16.4%), and total body weight regain of 53.9%([0.0-144.4]±31.3%). Conversion to RYGB resulted in peak %TBWL of 18.8% at 8 months, leveling off at 13.5% thereafter. Factors predictive of greater weight loss post-conversion included higher BMI at time of LSG (each 5 kg/m2 increase yielded 0.8% greater %TBWL [95% CI=0.5%-1%, p<0.0001]) and peak %EWL ≥40% after LSG (yielding 5.5% more %TBWL, 95%CI=3.9-7.1%, p<0.0001). Conversely, patients with GERD had 3.7% less %TBWL (95%CI=2.4-5.7%, p<0.0001), and those who had ≥20% weight regain after LSG had 4.1% less %TBWL (95%CI=2.5-5.7%, p<0.0001) after conversion. These factors were used to create BE-CALM, an algorithm to predict %TBWL one year after conversion to RYGB

Conclusions

Conversion from LSG to RYGB is effective for further weight loss. Patients who have higher starting BMI, ≥40% %EWL or <20% weight regain after LSG demonstrate the most effective weight loss post-conversion.