Thus, the aim of this work was to study in male and femalemice with obesity caused by the consumption of a sweet-fatdiet the effect of FGF21 on weight of body, liver, adipose tissues,tolerance to glucose, blood levels of hormones and metabolites,the amount of energy consumed with various typesof food, and expression of genes involved in the regulation ofmetabolic processes in the liver, white, brown adipose tissueand in the regulation of eating behavior in the hypothalamus. Here, FGF21 is linked to obesity due to melanocortin 4 receptor deficiency.