SIRT1 and fatty liver disease: However, according to our previous study demonstrating impairment of Nampt-NAD axis in aging and associated fatty liver, oral administration of nicotinamide riboside, a natural NAD precursor, completely corrected the fatty liver phenotypes induced by NAD deficiency alone or HFD, whereas adenovirus-mediated SIRT1 overexpression only partially rescued these phenotypes [7].