Further research is required to estimate the prevalence of depression and BDNF levels simultaneously to depict a more detailed picture of the interplay between depression and BDNF levels in the context of eating disorders, and to reach a clear understanding of the delicate interactions between BDNF levels and the entire nervous system to unravel the full scope of physiological, biochemical, and even anatomical influences this factor has on hunger regulation. This evidence concerns the gene BDNF and major depressive disorder.