The aim of this study was to investigate the effects of ileal interposition (IT) on glucose and insulin resistance (IR) in type 2 diabetic mellitus (T2DM), and the role of T-cell factor 7-like 2 (TCF7L2), formerly known as TCF4, in the downregulation of hyperglycemia following IT. This evidence concerns the gene TCF7L2 and diabetes mellitus.