FGF21 and obesity due to melanocortin 4 receptor deficiency: Experimentally, treatment with metformin for 14 weeks in mice was shown to significantly prevent high-fat diet-induced obesity and associated inflammatory response by increasing the expression of fibroblast growth factor 21 (FGF-21), which is a key metabolic hormone improving lipolysis in brown adipose tissue (BAT) to prevent fat accumulation [77].