INS and obesity due to melanocortin 4 receptor deficiency: Herein, we have applied state-of-the-art metabolomics to plasma and erythrocytes from a population encompassing children with obesity and IR, who were subjected to an OGTT and further stratified according to their insulin curve morphology: children showing an early insulin peak (t = 30 min), middle insulin peak (t = 60 min), and late insulin peak (t ≥ 90 min).