For example, FGF21 expression in liver tissues could be induced by fasting and a ketogenic diet (Badman et al., 2007; Inagaki et al., 2007), whereas overfeeding and obesity-inducing factors in the pancreas and white adipose tissue (WAT) (Oishi et al., 2011; Singhal et al., 2016a; Lundsgaard et al., 2017), by cold exposure in brown adipose tissue (BAT) (Chartoumpekis et al., 2011; Hondares et al., 2011; Keipert et al., 2015), and by exercises in skeletal muscle (Tanimura et al., 2016). The gene discussed is FGF21; the disease is obesity due to melanocortin 4 receptor deficiency.