Therefore, we propose that CCL2 serves a dual role as a potential biomarker of fitness and inflammation in obese children; CCL2 may aid the definition of fitness levels and demarcate a group of children who have more inflammation despite having similar metabolic profiles to other obese children but may require more intensive interventions to treat obesity-related inflammation. Here, CCL2 is linked to obesity due to melanocortin 4 receptor deficiency.