Finally, the balance of evidence seems to suggest alterations in secretion and/or action of incretin hormones in obesity and type 2 diabetes.20 For example, the secretion of GLP-1 is reportedly impaired in obesity, while GIP secretion may be enhanced.20 In the case of type 2 diabetes, the insulinotropic effect of GIP is largely diminished, although that of GLP-1 is better preserved. This evidence concerns the gene GCG and obesity due to melanocortin 4 receptor deficiency.