An increase of circulating FGF21 can be observed e.g., after acute exercising [3], long-term fasting [4], very low caloric diet [5], excessive intake of carbohydrates [6], in the postprandial period [7], after alcohol consumption [8], and lipid infusion [9], in type 2 diabetes (T2D) [10], metabolic syndrome (MS) and obesity [11,12]. This evidence concerns the gene FGF21 and obesity due to melanocortin 4 receptor deficiency.