Mental health, influenced by diet, genetics, and lifestyle, is essential to overall well-being. Diet significantly impacts mental health by affecting neurotransmitter synthesis, neuronal plasticity, and function. Nutrient deficiencies such as omega-3, B vitamins, magnesium, and zinc are linked to depression, anxiety, and cognitive deficits. During the prenatal period, adequate maternal folate, omega-3, and vitamin D intake supports fetal brain development and reduces neurodevelopmental disorders. Breast milk is crucial for the first 6 months in infancy and early childhood, with deficiencies in iron, zinc, and DHA leading to cognitive and behavioral issues. Essential nutrients like iron, zinc, selenium, and vitamins B12, B6, and D are vital for neuronal function and development. Adolescence, marked by rapid brain maturation and increased energy needs, can suffer from poor dietary choices that cause inflammation associated with depression and anxiety. Deficiencies in zinc, magnesium, and tryptophan during this stage contribute to mood swings and fatigue, while Mediterranean diets lower depression risk, contrasting with Western diets that may worsen mental health problems. In adulthood, diet influences stress management and cognitive performance, with anti-inflammatory diets rich in omega-3, polyphenols, and antioxidants enhancing mental health. Gut microbiota health, supported by probiotics and prebiotics, is linked to mood regulation, and adequate zinc, magnesium, and B vitamins prevent cognitive decline and mood disorders. For older adults, diet plays a role in preventing cognitive decline and dementia, with the Mediterranean diet associated with better cognitive health. Monitoring and addressing micronutrient deficiencies by supplementing omega-3 and B vitamins can improve mood and delay neurodegeneration. In conclusion, diet profoundly affects mental health by shaping brain structure, neurotransmitter function, and inflammation. A balanced, nutrient-rich diet can prevent and manage mental illness across the lifespan, and healthcare professionals should incorporate nutritional assessments into mental health care.