A Randomized Controlled Study Evaluating Bariatric Surgery as a Treatment for Severe NASH With Advanced Liver Fibrosis in Non-severe Obese Patients

Inclusion Criteria: * Provide written informed consent and agree to comply to the study protocol prior to enrolment. * BMI and Brunt Fibriosis score: * For F3 fibrosis patients: 35\>BMI≥ 30kg/m² ; Fibroscan ≥ 9kPa or FibrometreVM ≥0.526 predicting a F3 fibrosis score grade within 1 month before inclusion or F3 fibrosis score grade diagnosed by hepatic biopsy performed before inclusion. * For F4 fibrosis patients: 50\>BMI≥ 30kg/m² ; Fibroscan ≥ 15kPa predicting a F4 fibrosis score grade within 1 month before inclusion or F4 fibrosis score grade diagnosed by hepatic biopsy performed before inclusion. * Fibroscan ≥ 9kPa or FibrometreVM ≥0.526 predicting a F3 or F4 fibrosis score grade within 1 month before inclusion Or F3 or F4 fibrosis score grade diagnosed by hepatic biopsy performed before inclusion. * Patient should agree to have one liver biopsy during the screening period (before randomization, the randomization will be permitted after at least a second reading performed by pathologist of CHRU Lille to confirm the histological diagnosis of NASH with advanced fibrosis (F3-F4)) for the diagnosis purpose (if no histological biopsy within 1 month before inclusion is available) and one at the end of the treatment period for assessment of the treatment effects. * For patients with cirrhosis, patients must fulfil all the following criteria: Platelets \> 125 000, PT \> 80 %, Albumin \> 35 g/L, MELD score at inclusion \< 9, CPT score \< 6, No history of previous decompensation, No oesophageal varices (endoscopy), No vascular shunt, ASA score ≤ III, Alcohol consumption lower than 20g/day for women and 30g/day for men. * For hypertensive patients, hypertension must be controlled by stable dose of anti-hypertensive medication for at least 2 months prior to screening (and the stable dose can be maintained throughout the study). * Female participating in the study must be either of non-child bearing (surgically sterilized at 6 month prior to screening or postmenopausal) or using an efficient contraception: hormonal contraception (including patch, contraceptive ring etc) intra-uterine device or other mechanical contraception * Patient agrees to come to the study visits within the protocol-specified delay Exclusion Criteria: * Previous history of bariatric surgery (except gastric ring removed for more than 3 years). * Decompensated cirrhosis (MELD\> 7 CPT score\> 5, previous history of decompensation (encephalopathy, ascites, jaundice, varicose vein rupture) * Hepatocellular carcinoma * Platelets \<125 000; TP \<80%; bilirubin \<20 mmol / l; albumin \<35 g / L. * Other liver disease: alcohol consumption exceeding 20 g / day for women and 30g / day in men, HBV, HCV, CBP, CSP, autoimmune hepatitis, hemochromatosis, Wilson's disease, alpha-1 antitrypsin. * Being processed Cancer (chemotherapy, radiotherapy or hormone therapy) * HIV positive patients * Patients who had an acute cardiovascular episode, coronary Heart Disease (Angina pectoris, myocardial infarction, revascularization procedure), stroke or TIA (Transient Ischemic Attack) within the 6 months prior to screening Recent cardiovascular events (stroke, myocardial infarcts, etc…) in the past 6 months. * Severe chronic respiratory disease. * Severe chronic cardiac insufficiency (grade III and IV of NYHA classification). * Pregnant or breastfeeding women. * Simultaneous enrollment in another clinical trial. * Drug abuse within the past year. * Patient with contra-indication for bariatric surgery * Gastic Banding, Biliopancreatic diversion and all the new bariatric surgery techniques are forbidden because the study design allow only the laparoscopic sleeve gastrectomy or laparoscopic Roux-en-Y gastric Bypaass. * History of cancer, except: * Patients considered in remission for at least 5 years after onset of treatment. * Patients Treated and believed to be cured basal or squamous cell carcinoma of the skin or resected carcinoma of the cervix