A study on 35 T2DM patients having undergone bariatric surgery (23 RYGB and 12 SLG) indicated that bariatric surgery increased the insulin secretion rates and concentrations, slightly improved β-cell and rate sensitivity, and enhanced glucagon and GLP-1 response (Nannipieri et al., 2013). This evidence concerns the gene GCG and type 2 diabetes mellitus.