LEP and obesity due to melanocortin 4 receptor deficiency: We showed higher amounts of leptin in the circulation in HCD-fed model rats, suggesting leptin insensitivity or resistance (Myers et al., 2008) in this complex model, which were well documented in previous reports that most overweight people and diet-induced common obesity rodent models had enhanced levels of circulating leptin (Spiegelman and Flier, 2001; Enriori et al., 2007).