In a few studies performed on rats and mice ofboth sexes, sex differences in the expression of FGF21 in liver(Lee et al., 2016; Chukijrungroat et al., 2017) and other tissues(Gasparin et al., 2018) were observed, exhibiting differential manifestation in obesity and starvation (Bazhan et al., 2019).These data suggest that the physiological and pharmacologicaleffects of FGF21 may vary in individuals of different sexes. Here, FGF21 is linked to obesity due to melanocortin 4 receptor deficiency.