Second, while we might expect this observed reduction in leptin/insulin sensitivity to result in increased dopamine function, analogous to reduced leptin/insulin signals in food-restriction, most studies report decreased dopamine function in obesity (Di Chiara et al., 1998; Wang et al., 2001a; Davis et al., 2008; Geiger et al., 2008, 2009; Li et al., 2009; Vucetic and Reyes, 2010). This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.