FGF21 and Obesity: Moreover, in contrast to a HFD-induced thermogenesis of subcutaneous fat to counteract excess energy intake, adult rats that were protein deficient during the perinatal period blunted this adaptation by increasing G9a, a histone methyltransferase of FGF21, thus attenuating the HFD-mediated FGF21 up-regulation and leading to an obesity-prone characteristic [42].