However, an increasing number of studies indicates that AhR plays an important role in lipid metabolism, causing lipid metabolic diseases such as obesity (Kerley-Hamilton et al., 2012), non-alcoholic fatty liver disease (NAFLD) (Moyer et al., 2017), and type 2 diabetes (T2D) (Wang et al., 2011). Here, AHR is linked to obesity due to melanocortin 4 receptor deficiency.