Materials and Methods: The Investigators will screen patients with obesity, NAFLD fibrosis score (NFS) >0.676 and FibroScan > 9.5 kPA who have a high probability of NASH with advanced stage of fibrosis.~Participants will undergo liver biopsy to make diagnosis according to the Steatosis Activity Fibrosis (SAF) score algorithm. Subjects with BMI ≥ 30 and ≤50 kg/m2, age 25-65 years and F3-F4 fibrosis stage at liver biopsy will be included and randomized 1:1 to RYGB or VLCD. Anthropometric parameters, body composition with DEXA and liver function with blood samples will be assessed at the enrolment. A mixed meal metabolic test will be also performed to evaluate insulin sensitivity and secretion. These procedures will be repeated after 25% weight loss. Expectation: The Investigators expect a reduction of 2 points of histological fibrosis after 25% weight loss following either metabolic surgery or dieting. The investigators foresee also reversal of NASH, improvement of metabolic syndrome and glycemic control, changes in insulin sensitivity and secretion, changes in lipid profile, in NASH liver markers, in Fibroscan variables and in body composition
Background: Non-Alcoholic Steatohepatitis (NASH) represents one of the stages of Non-Alcoholic Fatty Liver Disease (NAFLD) with a very high risk to evolve in cirrhosis and hepato-carcinoma.~Currently, the only diagnostic method is a liver biopsy that remains the gold standard for characterizing liver histologic alterations and fibrosis stages. There is no specific treatment for NASH, in fact no drugs are currently licensed specifically for treating this disease.~Aim: Our aim is to conduct a non-inferiority, randomized-controlled trial (RCT) comparing Roux-en-Y Gastric bypass (RYGB) with an intensive lifestyle modification plan (Very low-calorie diet, VLCD) for the reduction of advanced stages of fibrosis in subjects with obesity and NASH after 25% weight loss.