Hepatic Trp metabolism via tryptophan 2,3-dioxygenase (TDO2) and indoleamine 2,3-dioxygenase (IDO) generates kynurenine (Kyn), which activates aryl hydrocarbon receptor (AHR) signaling to promote obesity-associated hepatic steatosis (Rojas et al., 2021). This evidence concerns the gene AHR and obesity due to melanocortin 4 receptor deficiency.