Weight loss, by changes in lifestyle or metabolic surgery, improves glycaemia in type 2 diabetes [19]–[21].The beneficial impact of Roux-en-Y gastric bypass surgery on diabetes control is associated with enhanced β-cell function and improved insulin sensitivity which has been attributed, in part, to an exaggerated post-prandial GLP-1 response [22]–[24]. This evidence concerns the gene GCG and type 2 diabetes mellitus.