Brown Adipose Tissue Activity in Gilbert's Syndrome

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