Depression is a global health issue that is socially and economically expensive. The gut microbiome influences depression, and fermented foods contain bacteria that contribute to the ecology of the gut microbiome. We performed a systematic review of clinical research that examines the relationship between fermented food and depression by conducting an electronic search of four academic databases using the search terms fermented, fermented foods, fermentation, and depression. The inclusion criteria are: inpatient, outpatient, and community settings; human participants age 5-110 years old; any diagnosis of depression; daily ingestion of fermented foods regardless of ingredients; written in English; published full text articles accessible through St. Catherine University; random controlled trials, case reports, cross-sectional studies, cohort studies, and clinical trials; and any measured change in depression after daily ingestion of fermented food. We identified 64 articles, and only two met the inclusion criteria. Both studies indicate a positive trend between fermented food supplementation and improvement in depression. Results are presented in a narrative synthesis, however, there were too few studies to draw major or significant conclusions. Researching multifaceted issues including the gut microbiome and depression in a reductive manner is paradoxical and inadequate. We suggest a more holistic approach with epistemological and ontological assumptions that account for the complexities and synergies in the human body
