Finally, specific gut bacteria have also been associated with altered bile acid composition, which also seem to play an important role in diabetes, obesity, non-alcoholic fatty liver disease and other metabolic diseases via the farnesoid X receptor (FXR) and G protein-coupled bile acid receptor (GPCR) signaling pathway [29–31]. The gene discussed is NR1H4; the disease is obesity due to melanocortin 4 receptor deficiency.