Investigation on the Role of Gut-liver Axis for Non-alcoholic Steatohepatitis Through Bariatric Surgery

The investigators anticipate to recruit 140 morbidly obese patients who will receive bariatric surgery including 100 patients receiving sleeve gastrectomy (SG) and 40 receiving gastric bypass surgery (GB). Liver biopsy will be performed during the operation to confirm the histological scores of NAFLD severity. The investigators expect to have 50% NASH and 50% NAFL patients from these morbidly obese patients based on previous domestic data. (i.e. 50 patients receiving SG to have NASH and 50 patients receiving SG to have NAFL; 20 patients receiving GB to have NASH and 20 patients receiving GB to have NAFL.) In this study, the investigators have two study objectives which are as follows. 1. The first objective is to discover potential mechanisms among gut-liver axis for preventing or promoting NAFL to NASH by comparing (1) fecal microbiome composition and metabolomics, (2) peripheral blood biochemistry, metabolomics, immune cell phenotypes, and cytokines (3) portal vein biochemistry, metabolomics, immune cell phenotypes, and cytokines (4) Liver metabolomics and RNA-seq (5) gut permeability test (lactulose/mannitol challenge) (6) host genetic susceptibility for NAFLD (PNPLA3 and TM6SF2) between the tissue-proved NASH and NAFL patients in this study with a cross-sectional comparison. 2. The second objective is to longitudinally investigate the potential mechanisms of bariatric surgery for improving NASH via a gut-microbiota dependent pathway. Clinical and experimental data before (baseline) and after (1st, 3rd, 6th months) bariatric surgery will be collected which include (1) non-invasive evaluation of NAFLD severity (Fibroscan, MRI-PDFF (proton density fat fraction) and MRE), (2) blood biochemistry, metabolomics, immune cell phenotypes, and cytokines (3) fecal microbiome and metabolomics (4) gut permeability test (5) liver biopsy histology (if available)