BDNF and major depressive disorder: Overweight and obese individuals have lower levels of BDNF, which deregulates food intake.55,56 Calorically high, obesity-inducing diets can further reduce BDNF levels in the brain and can impair neural plasticity and neurogenesis.55 The neurotrophic hypothesis of depression posits that a reduction in the concentration of BDNF plays a critical role in depression as well.57