Inclusion criteria (all participants):  Female and male subjects aged 18 years or older Proficient German (including written)  Inclusion criteria for Group 1:  Class II-III obesity (BMI≥35kg/m2) Planned for bariatric surgery (Roux-en-Y gastric bypass)  Inclusion criteria for Group 2:  Normal body weight (BMI 18.5-24.9kg/m2) Absence of evidence of any active or chronic disease as judged by the Clinical Investigator  Exclusion criteria:  Incapacity to give informed consent Diabetes according to WHO (World Health Organization ) definition (Fasting plasma glucose ≥7.0mmol/l, random plasma glucose ≥11.1mmol/l, HbA1c ≥6.5%) Previous or current neurological or severe psychiatric illness Current or planned pregnancy or breastfeeding Claustrophobia MRI-contraindications (pacemaker/defibrillator, neurostimulator, drug pump, cochlear implant, heart valve/vascular clips, shunt valve)