Improving Glucose and Lipid Metabolism Through Caloric Restriction Using Diet or Surgery (CRUDOS)

Inclusion Criteria: * Age: 18-60 years * BMI 35-45 * Sagittal abdominal diameter ≤38.5cm * For participants with type 2 Diabetes Mellitus, a disease duration of no more than 10 years, treated with 0-3 oral antidiabetic drugs and/or with diet. HbA1C 48-80mmol/mol at baseline visit. Exclusion Criteria: * Diabetes complications: proliferative retinopathy, maculopathy, chronic renal failure stadium 3 with an eGFR\<60, foot ulcers, symptomatic neuropathy * Medications within 3 months: Insulin, Thiazolidinediones * Any other condition with in the opinion of the investigator would render the participant unsuitable for inclusion in the study and /or for the patients safety * Judgment by the investigator that the subject should not participate in the study if considers subject unlikely to comply with study procedures, restrictions and requirements * Pregnant or planning to be pregnant during the study. * Known or suspected history of significant drug abuse. * History of alcohol abuse or excessive intake of alcohol as judged by investigator. * History of severe allergy/hypersensitivity or ongoing allergy/hypersensitivity, as judged by the investigator * Sleep apnoea * Any previous serious cardiovascular event, stroke, acute myocardial infarction. * Any condition when MRI-PET is contraindicated such as, but not limited to, having a pacemaker or claustrophobia