It has recently been shown that the anti-diabetic effectof FGF21 in genetically obese mice (ob/ob and Ay mice) appearsonly in males (Berglund et al., 2009; Makarova et al.,2020; Makarova et al., 2021b), whereas in mice with obesitycaused by HFD it is manifested both in females and males.In mice with SFD-induced obesity (SFDIO), the effects ofFGF21 have been shown in males (Coskun et al., 2008), whilein females, they have not been studied. Here, FGF21 is linked to obesity due to melanocortin 4 receptor deficiency.