NR1H4 and cystic fibrosis: There could be numerous explanations for the increased excretion of bile acids in CF stool: (i) altered farnesoid X receptor (FXR) signaling, a negative feedback cascade that ultimately regulates bile acid synthesis (240), (ii) hindered absorption of bile acids in the ileum and colon due to the thickened mucosal layer (241), (iii) altered functionality of the apical sodium-dependent bile acid transporter (ASBT), an active transporter of bile acids largely active in the ileum (242), and (iv) the prevalence for small intestine bacterial overgrowth (SIBO) in the CF population (183, 243).