FGF21 has been suggested to be a potential therapy for obesity and type 2 diabetes, with several previous studies having shown that the induction of FGF21 expression leads to significant metabolic improvements, including reductions in fasting glucose, insulin, and triacylglycerol (TG) concentrations in high-fat diet (HFD)-fed and leptin-deficient obese mice [15,16,17]. Here, INS is linked to obesity due to melanocortin 4 receptor deficiency.