FGF21 and metabolic disease: In contrast, FGF21 inhibited lipolysis in adipocytes of fasted mice and attenuated torpor induced by KD, indicating that Fgf21 may be a “thrifty gene.” Serum FGF21 levels are increased in patients with metabolic diseases having insulin resistance including NAFLD, type 2 diabetes, Cushing's syndrome, and HIV-1-induced lipodystrophy.