FABP5 and obesity due to melanocortin 4 receptor deficiency: In prior studies, FABP5 was highly and exclusively expressed in enteroendocrine K cells, maintaining the normal level of glucose-dependent insulinotropic polypeptide (GIP) (Sommer and Mostoslavsky 2014), which regulates diet-induced obesity in response to fat ingestion (Shibue et al. 2015).