FNDC5 and obesity due to melanocortin 4 receptor deficiency: For example, a cross‐sectional analysis revealed that youth living with obesity had higher irisin levels at rest [141.2 ng/ml, (IQR 90.1–195.9)] compared to a healthy weight control group [107.6 ng/ml, (IQR 89.5–138.3); p = 0.024] (Çatlı et al., 2016).