Participants, eligibility criteria, setting
This study was approved by the local ethics committee (Kantonale Ethikkommission Zurich, Zurich, Switzerland, number 2017 – 01,790) as well as by the national authorization and supervisory authority for drugs and medical products (Swissmedic Bern, Switzerland, notification number 2017DR2183).Inclusion criteria were defined as patients between 18 and 65 years old being scheduled for primary bariatric surgery with a BMI > 35 kg/mAll participants of the study provided written and informed consent to participate in this trial. It was registered before patient enrollment on 
www.clinicaltrials.gov
(NCT 03,338,907; date of registration: 09/11/2017) and is reported according to the consolidated standards of reporting trials (CONSORT) checklist [