Disease burden from psychiatric disorders is an important public health issue worldwide, and should be addressed proactively. Because the development of psychiatric disorders involves both genetic and environmental factors, as well as their interactions, lifestyle intervention is a feasible treatment and prevention strategy. The human brain uses a substantial portion of the body's total energy and nutrient intake. Nutrients strongly influence both brain structure and function, and nutrition also affects neurodevelopment and neurotrophic function. It has been recognized in recent years that diet and nutrition may be an important factor contributing to psychiatric morbidity, and that prevention or treatment of psychiatric disorders could be conducted by addressing diet and nutrition. Against this background, in 2013 we founded the International Society for Nutritional Psychiatry Research (ISNPR). The aim of the present paper is to provide a set of practical recommendations for the prevention and treatment of depression based on the ISNPR statement and the review by Opie et al. Here, we introduce Opie's five key dietary recommendations and state our hypotheses for improving mental health: (1) follow traditional dietary patterns, such as the Mediterranean, Norwegian, or Japanese diet; (2) increase consumption of fruits, vegetables, legumes, whole-grain cereals, nuts, and seeds; (3) consume higher amounts of foods rich in omega-3 fatty acids; (4) replace unhealthy foods with wholesome nutritious foods; (5) limit intake of processed foods, fast foods, commercial baked goods, and sweets; and (6) be mindful of probiotic gut bacteria. The possible biological mechanisms by which nutrition might affect mental state are not known in depth, and full associations between nutrition and mental disorders have not been examined in randomized controlled trials. However, the existing evidence suggests that a combination of healthy dietary practices may reduce the risk of developing depression. As dietary practices and lifestyle can be changed by individuals at any time, new integrated approaches to mental health from the viewpoint of diet and nutrition-that is, nutritional psychiatry-could be applicable to a wide population. Gathering the findings of high-quality studies and implementing nutritional psychiatry within clinical practice are important tasks for the future.
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