Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), a major global public health concern, is commonly associated with obesity, diabetes, and dyslipidemia. MASLD is currently the most common cause of chronic liver disease affecting about 80% of people with obesity, ranging from simple fat deposits in the liver to Metabolic Dysfunction-Associated Steatohepatitis (MASH), cellular injury, advanced fibrosis, cirrhosis, or hepatocellular carcinoma. Patients with MASH are also at risk for cardiovascular disease and mortality. There is no universally approved medication for MASH. Weight loss remains the cornerstone of MASH treatment. Patients meeting the inclusion and exclusion criteria and who give informed consent will be enrolled in the trial and undergo the baseline liver biopsy (if none available). Approximately 120 patients with MASH and liver fibrosis (F1-F4 in baseline liver biopsy) will be randomized in a 1:1 ratio to metabolic surgery or medical treatment (incretin-based therapies ± other medical therapies for MASH) and followed for 2 years at which time a repeat liver biopsy will be performed for the assessment of the primary end point.

FLAMES (Fibrosis Lessens After Metabolic Surgery) is a 2-arm randomized, controlled, pathologist-blinded multicenter study with 2 parallel groups of patients with MASH, liver fibrosis, and obesity who will either receive metabolic surgery or incretin-based therapies (semaglutide \[injection or oral\], tirzepatide \[injection\], or liraglutide \[injection\]) for 2 years to assess the effects of advanced surgical and medical therapies in liver histology in patients with obesity, biopsy-proven MASH, and liver fibrosis. With genuine uncertainty in the expert medical community and literature over which treatment will result in a greater improvement in histopathological features of MASH and liver fibrosis, the investigators aim to compare metabolic surgery and incretin-based therapies head-to-head. Adult patients with BMI between 35 - 60 kg/m\^2, Fibrosis-4 (FIB-4) index ≥ 1.3, liver stiffness measure (LSM) ≥ 12 kPa by vibration-controlled transient elastography (VCTE) using FibroScan (or similar non-invasive tests) who meet the contemporary eligibility criteria for metabolic surgery will be eligible for participation. Patients meeting the inclusion and exclusion criteria and who give informed consent will be enrolled in the trial and undergo the baseline liver biopsy. Approximately 120 patients with MASH and liver fibrosis (F1-F4 in baseline liver biopsy) will be randomized in a 1:1 ratio to metabolic surgery or medical treatment (incretin-based therapies ± other medical therapies for MASH) and followed for 2 years at which time a repeat liver biopsy will be performed for the assessment of the primary end point. The primary site of this multicenter, international, randomized controlled trial (RCT) is at the Cleveland Clinic main campus in Cleveland, Ohio, USA.