In this work, we aimed to unveil the relationship between circulating metal species and the insulin secretion profile in children and adolescents with obesity and IR, who were stratified into three subgroups based on their individual response to an OGTT: subjects with an early insulin peak (t = 30 min), subjects with a middle insulin peak (t = 60 min), and subjects with a late insulin peak (t ≥ 90 min). This evidence concerns the gene INS and obesity due to melanocortin 4 receptor deficiency.