Reduced serum BDNF levels were shown to be phenotypically associated with an impaired cognitive functioning and hyperactivity, but also with severe obesity (Gray et al., 2006), while increased serum BDNF levels were found in overweight to obese individuals after losing weight after a reduced-calorie diet (Araya et al., 2008). This evidence concerns the gene BDNF and obesity due to melanocortin 4 receptor deficiency.