Fibroblast Growth Factor 21 (FGF21) is a growth factor that belongs to the FGF family. FGF family proteins play a central role during prenatal development and postnatal growth and regeneration of mamy tissues, by promoting cellular proliferation and differentiation. FGF21 is a potent activator of glucose uptake on adipocytes, protects animal from diet-induced obesity when overexpression in transgenic mice, and lower blood glucose and triglyceride levels when therapeutically adiministered to diabetic redents. FGF21 is produced by hepatocytes in reponse to free fatty acid stimulation of a PPARa/RXR dimeric complex. This situation occurs clinically during starvation, or following the ingestionof a highly-fat/low-carbohydrate diet. Upon FGF21 secretion, white adipose tissue is induced to release free fatty acids from triglyceride stores. Once free fatty acid reach hepatocytes, they are oxidized and reduced to acetyl-CoA. The acetyl-CoA is recombined into 4-carbon ketone bodies, release, and transported to peripheral tissue for TCA processing and energy generation.