The Franciscus Obesity NASH Study

Inclusion Criteria: Participants must fulfil all of the inclusion criteria (unless otherwise specified) for enrolment in the study. 1. Participants must fulfil the criteria of the International Federation for the Surgery of Obesity (IFSO) at screening. 2. Participants must be able to understand the nature of the study and written informed consent must be obtained before any study specific interventions are performed. The cardiac function of a subset group of 30 subjects aged 35 years and older with low transient elastography measurements (≤F1) and no known cardiac disease, hypertension or diabetes mellitus will be compared with a similar number of patients with high transient elastography measurements (≥F3) and no known cardiac disease, hypertension or diabetes mellitus. These patients will be consecutively included. The investigators will perform a liver biopsy during endoscopic bariatric surgery in the patients with an elevated transient elastography measurement (≥F2; suggesting fibrosis and therefore the presence of NASH) in order to correlate the histological diagnosis to the clinical diagnosis based on elastography. In those patients in whom the diagnosis of NASH is confirmed by histology, more detailed follow up in a separate program at the department of gastroenterology is indicated according to the current guidelines. Exclusion Criteria: Patients who meet any of the following criteria at screening (unless otherwise specified) will be excluded from the study: 1. Participants younger than 18 years or older than 65 years 2. Participants with an established diagnosis of liver pathology like, but not limited to: 1. Hepatitis B 2. Hepatitis C 3. Autoimmune hepatitis 4. Wilson's disease 5. Hemochromatosis 6. Primary biliary cholangitis 7. Primary sclerosing cholangitis 8. Alcoholic liver disease 3. Histologically documented liver cirrhosis (fibrosis stage F4), at screening or in a historical biopsy. 4. Participants with active HIV infection and/or treatment. 5. Participants with diagnosed malignancies with or without active treatment. 6. Participants with a history or evidence of any other clinically significant condition or planned or expected procedure that in the opinion of the investigator, may compromise the patient's safety or ability to complete the study. 7. The participant does not understand Dutch.