The current work further reinforces this hypothesis, because the main difference between the obesity and normal weight and anorexia nervosa subjects is the higher fat mass; therefore, adipose tissue could be involved in the circulating irisin concentration differences observed depending on the BMI as reinforced in preliminary experiments assaying FNDC5/irisin immunodetection in adipose tissue from NW and OB individuals in Figure 4. Here, FNDC5 is linked to obesity due to melanocortin 4 receptor deficiency.