1. Department of Gastrointestinal and Paediatric Surgery, Oslo University Hospital, University of Oslo, Oslo, Norway
2. Department of Gastrointestinal Surgery, Vestfold Hospital Trust, Norway
3. Department of Endocrinology, Morbid Obesity and Preventive Medicine, Oslo University Hospital, Oslo, Norway
4. Morbid Obesity Centre, Vestfold Hospital Trust, Norway
5. Oslo Centre for Biostatistics and Epidemiology, Research Support Services, Oslo University Hospital, Oslo, Norway
6. Morbid Obesity Centre, Department of Medicine, Vestfold Hospital Trust, Tønsberg, Norway