Given the elevated prevalence of metabolic syndrome and its hepatic manifestation, in the general population, differentiating between hepatic steatosis due to viral infection (viral steatosis) and hepatic steatosis due to a coexisting metabolic syndrome (metabolic steatosis) remains a challenge [9]; however, with the PPAR-α–FGF-21 axis being involved in the pathogenesis of both, the administration of FGF-21 analogues could be of benefit without the need to discriminate between the two. Here, FGF21 is linked to viral infectious disease.