FGF21 and obesity due to melanocortin 4 receptor deficiency: It is possible that in SFDIOmales, the FGF21-induced improvement in glucose tolerancewas associated with a decrease in plasma concentration ofleptin and fatty acids which are key risk factors for insulinresistance at obesity (Yang et al., 2018; Zhang Q. et al., 2019).Zhao and coauthors, using genetic approaches and a leptinneutralizing antibody, demonstrated that in obese mice, apartial reduction of plasma leptin levels restores hypothalamicleptin sensitivity and effectively enhances glucose toleranceand insulin sensitivity (Zhao et al., 2019).