Several studies of the fat mass and obesity-associated gene (FTO) have indicated that environmental factors such as diet composition and physical activity level may modify the genetic susceptibility to develop obesity (Andreasen et al. 2008; Li et al. 2012; Sonestedt et al. 2011; Sonestedt et al. 2009). This evidence concerns the gene FTO and obesity due to melanocortin 4 receptor deficiency.