FGF21 plasma levels are increased in type 2 diabetes, obesity, nonalcoholic fatty liver disease (NAFLD) and dyslipidemia (35, 36, 37, 38, 39), but injection of FGF21 in animal models of insulin resistance has been shown to improve this condition (9, 10, 11, 13, 14). This evidence concerns the gene FGF21 and obesity due to melanocortin 4 receptor deficiency.