INS and obesity due to melanocortin 4 receptor deficiency: O mice developed a mild degree of obesity but it was not enough to induce metabolic alterations or oxidative stress. These animals exhibited a healthy expansion of retroperitoneal white adipose tissue (rpWAT) and the liver showed no signs of lipo-toxicity while OE mice were insulin resistant although achieving a similar body weight. In the rpWAT they presented a reduced generation of ROS, even below physiological levels (C: 1651.0 ± 212.0; O: 3113 ± 284.7; OE: 917.6 ± 104.4 RFU/mg protein. C vs. OE p < 0.01).