Diet and Psychosis: A Scoping Review

Introduction: Schizophrenia spectrum disorders (SSD) represent a cluster of severe mental illnesses. Diet has been identified as a modifiable risk factor and opportunity for intervention in many physical illnesses and more recently in mental illnesses such as unipolar depression; however, no dietary guidelines exist for patients with SSD. Objective: This review sought to systematically scope the existing literature in order to identify nutritional interventions for the prevention or treatment of mental health symptoms in SSD as well as gaps and opportunities for further research. Methods: This review followed established methodological approaches for scoping reviews including an extensive a priori search strategy and duplicate screening. Because of the large volume of results, an online program (Abstrackr) was used for screening and tagging. Data were extracted based on the dietary constituents and analyzed. Results: Of 55,330 results identified by the search, 822 studies met the criteria for inclusion. Observational evidence shows a connection between the presence of psychotic disorders and poorer quality dietary patterns, higher intake of refined carbohydrates and total fat, and lower intake or levels of fibre, ω-3 and ω-6 fatty acids, vegetables, fruit, and certain vitamins and minerals (vitamin B₁₂ and B₆, folate, vitamin C, zinc, and selenium). Evidence illustrates a role of food allergy and sensitivity as well as microbiome composition and specific phytonutrients (such as L-theanine, sulforaphane, and resveratrol). Experimental studies have demonstrated benefit using healthy diet patterns and specific vitamins and minerals (vitamin B₁₂ and B₆, folate, and zinc) and amino acids (serine, lysine, glycine, and tryptophan). Discussion: Overall, these findings were consistent with many other bodies of knowledge about healthy dietary patterns. Many limitations exist related to the design of the individual studies and the ability to extrapolate the results of studies using dietary supplements to dietary interventions (food). Dietary recommendations are presented as well as recommendations for further research including more prospective observational studies and intervention studies that modify diet constituents or entire dietary patterns with statistical power to detect mental health outcomes.