Brown Adipose Tissue Activity in Gilbert's Syndrome

The goal of this case-control study is to investigate energy metabolism and brown adipose tissue (BAT) activity in individuals with Gilbert's syndrome (GS) and controls. The main focus of the study is to analyze: 1. the link between bilirubin metabolism and metabolic health. 2. energy metabolism and body composition in individuals with Gilbert's syndrome and control subjects 3. brown adipose tissue activity in Gilbert's syndrome and healthy controls. Participants will undergo the following investigations: 1. cold exposure 2. PET-CT imaging with 18-F-FDG 3. MRI imaging of liver, abdominal fat and muscle 4. blood sampling 5. indirect calorimetry 6. bioelectrical impedance analysis 7. infrared thermography Researchers will compare individuals with GS and control subjects in terms of metabolic health, body composition and BAT activity.

Inclusion Criteria: * written consent, age between 18 and 65 years of age, liver marker (AST, ALT, GGT) \< 2x of the upper norm range, non-smoker, moderate physical activity, ability to understand the requirements of the course of study Cases: (Gilbert-Syndrom): * Total bilirubin in the blood \> 1.2 mg/dL (17.1 μM) * Unconjugated (indirect bilirubin) \> 1 mg/dL Controls (non-Gilbert-Syndrom): * Total bilirubin in the blood ≤ 1.2 mg/dL (17.1 μM) * Unconjugated (indirect bilirubin) ≤ 1 mg/dL Exclusion Criteria: * age \< 18 or \> 65 years; having current or any history of cardio-pulmonary, metabolic or musculoskeletal disease; breastfeeding or was/potentially pregnant; liver diseases incl. hep A and B; kidney diseases; active tumor disease; persons with an organ transplant; not willing to meet the demands of the study; not being weight stable (± 5% body mass; self-reported) for at least the 3 months prior to their involvement; or any conditions or concurrent behaviour (including medication) that may have posed undue personal risk to the participant, introduce bias to the study or were influencing liver marker in the last 5 weeks. Cases: (Gilbert-Syndrom): * Total bilirubin in the blood ≤ 1.2 mg/dL (17.1 μM) * Unconjugated (indirect bilirubin) ≤ 1 mg/dL Controls (non-Gilbert-Syndrom): * Total bilirubin in the blood \> 1.2 mg/dL (17.1 μM) * Unconjugated (indirect bilirubin) \> 1 mg/dL