GIP and Insulin resistance: To determine whether RYGB changes the gut microbiota in a correlational manner or a coincidental manner, BMI and 12 metabolic indices, including alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transpeptidase (gamma-GT), insulin resistance index (HOMA-IR), fasting glucose (FBS), fasting insulin, fasting c-peptide, glycosylated hemoglobin (HbA1c), triglyceride, ghrelin, gastric inhibitory polypeptide (GIP), and leptin, were correlated with alterations in the gut microbiome (Supplemental Table 1, 2).