AhR deficiency significantly reduced weight gain and adiposity, increasing the protein and mRNA expression of fibroblast growth factor 21 (FGF21), which activates thermogenesis in brown adipose tissue (BAT) and gWAT, thus increasing metabolic rate and energy expenditure, preventing obesity induced by a high-fat diet (Girer et al., 2019), making it a potential target for obesity treatment. The gene discussed is FGF21; the disease is obesity due to melanocortin 4 receptor deficiency.