Research has identified numerous pathways through which diet may affect mental health, including modulation of inflammation, oxidative stress, epigenetics, mitochondrial dysfunction, gut microbiota, tryptophan–kynurenine metabolism, the hypothalamic–pituitary–adrenal (HPA) axis, neurogenesis and brain‐derived neurotrophic factor (BDNF) and obesity (Marx et al. 2021). The gene discussed is BDNF; the disease is obesity due to melanocortin 4 receptor deficiency.