Conversely, reduced body weight gain has been observed in diet-induced obesity models in a GIPr−/− knock-out mouse (49), upon immunization with GIP to generate antagonistic antibodies, and upon administration of the GIPr peptide antagonist Pro3GIP or ablation of GIP-producing K cells (50–53). This evidence concerns the gene GIPR and obesity due to melanocortin 4 receptor deficiency.