This chapter explores the intricate relationship between nutrition and mental health, focusing on how dietary patterns and specific nutrients influence psychiatric disorders. Essential nutrients such as B vitamins, omega-3 fatty acids, antioxidants, polyphenols, and tryptophan regulate neurotransmitter synthesis, mitochondrial function, brain inflammation, and oxidative stress. These mechanisms are central to the development and progression of psychiatric conditions like depression, anxiety, schizophrenia, and attention-deficit hyperactivity disorder. Particular emphasis is placed on the gut-brain axis, mitochondrial function, and epigenetic regulation as critical pathways through which nutrition impacts mental health. The chapter also underscores the protective effects of the Mediterranean diet and the potential harm of processed foods in exacerbating psychiatric symptoms. Understanding these nutritional mechanisms offers valuable insights for integrating dietary interventions into mental health care, leading to better clinical outcomes in psychiatric disorders.