FNDC5 and obesity due to melanocortin 4 receptor deficiency: Although recent studies have shown that the increased irisin levels due to physical exercise are associated with signs of decreased metabolic syndrome and insulin resistance (Elizondo-Montemayor et al., 2018[23]), there are contradicting results concerning the outcomes of exercise interventions on the conversion of white adipose tissue to brown adipose tissue and their role in the prevention of obesity.