Our systematic review and meta-analysis evaluates all major bariatric procedures (RYGB, SG, AGB, and BPD) and their effects on a wide range of glycemic (HbA1c, fasting blood glucose (FBG), postprandial glucose (PPG)) and metabolic markers (fasting insulin, homeostatic model assessment of insulin resistance (HOMA-IR), C-peptide) in people with T2DM. This evidence concerns the gene INS and Insulin resistance.