FGF21 and obesity due to melanocortin 4 receptor deficiency: For example, the effect of FGF21 on glucose uptake by myotubes is similar to the effect of insulin (Rosales-Soto et al., 2020), with upregulated FGF21 expression in skeletal muscle protecting against diet-induced obesity and insulin resistance (Kim et al., 2013; Pereira et al., 2017).