FGF21 and obesity due to melanocortin 4 receptor deficiency: The red circle (right quadrant) covers metabolic foundations such as obesity, adipose tissue, diabetes, liver, type 2 diabetes, high-fat diet, liver fibrosis, insulin sensitivity, metabolism, and FGF21; the purple circle (left quadrant) contains adipokine-focused terms including adiponectin, leptin, nonalcoholic steatohepatitis (NASH), fibrosis, resistin, visfatin, bariatric surgery, and biomarkers.