FGF21 and hyperlipidemia: Downregulated hepatic FGF21 in ketogenic diet-fed mice altered the expressions of lipid and ketone metabolism-related genes in the liver, and leads to fatty liver, lipemia, and decreased serum ketone.557 FGF21 stimulates hepatic gluconeogenesis and ketogenesis in the liver during fasting and starvation558,559 by inducing the expression of PGC-1α.559FGF21 knockout mice fail to induce PGC-1α expression and have impaired gluconeogenesis and ketogenesis in response to a prolonged fast.559 However, the mechanisms for the regulation of FGF21 on liver metabolism need to be further explored.