Systematic review of probiotic interventions in healthy and psychiatric populations shows neurobiological associations

Though microbial interventions such as probiotics and fecal microbiota transplantation have had a growing body of evidence suggesting their efficacy in alleviating the symptoms of psychiatric illnesses, their exact mechanisms of action and impacts on the brain are still not fully characterized. The aim of this review is to compile and summarize the current literature regarding neurobiological changes associated with microbial interventions targeting psychiatric symptoms in healthy and psychiatric populations. A systematic search of four databases was conducted using key terms related to neuroimaging, microbial interventions, and psychiatric illnesses and/or symptoms. All results were then evaluated based on specific eligibility criteria. 10 studies met eligibility criteria and were included in this systematic review. Three of the five healthy control studies and all five of the studies conducted within psychiatric populations, observed significant neurobiological changes associated with probiotic intervention either in areas with psychiatric relevance, in the direction of a healthier profile, or correlated with improved psychiatric and/or affective symptoms. The interventions used in these studies consisted of probiotics with bacterial species primarily from the lactobacillus and bifidobacterium genera, at doses ranging from 1–900 billion CFU, taken for durations ranging from 4 weeks to 6 months. The findings from this review suggest that probiotic intervention may be associated with neurobiological changes, and that these changes could play a role in ameliorating psychiatric symptoms. More research is needed to replicate these findings, explore other psychiatric populations and microbial interventions, and fully elucidate the mechanisms driving these promising neurobiological and clinical changes.