Sample Size
The sample size was calculated using G*power Version 3.1.9.5, based on a large effect size of 0.8, corresponding to a mean difference in %EWL two years after re-sleeve gastrectomy of at least 8% (±sd 10) between BLSG and NBLSG with a power of 80% and a significance level of 0.05. This resulted in a minimum required sample size of 26 patients per group. Considering a possible loss of patients to follow-up, an additional 10% increase in sample size was included, resulting in a minimum of 57 patients enrolled.