While a positive association between GDF15 and weight, BMI, and fat mass is evident when controls and obese subjects are analysed together, the negative correlation between GDF15 and body fat percentage observed when focussing exclusively on the cohort of patients with obesity suggests that GDF15 levels may reflect compensatory mechanisms related to adiposity regulation in individuals with obesity. Here, GDF15 is linked to obesity due to melanocortin 4 receptor deficiency.