Probiotics/prebiotics/synbiotics and human neuropsychiatric outcomes: an umbrella review

The neuropsychiatric effects of probiotics, prebiotics, and synbiotics have been gaining attention since the rise of microbial-gut-brain axis research. Nevertheless, some of the findings are inconsistent, and few studies have analysed the similarities and differences in the neuropsychiatric effects of the three comprehensively. To reveal the respective neuropsychiatric effects of probiotics, prebiotics, and synbiotics and synthesise the similarities and differences among the three effects, 47 meta-analyses with 12 types of neuropsychiatric results were integrated under an umbrella review. Probiotics, prebiotics, and synbiotics intake might all be associated with improvements in some neuropsychiatric outcomes, including neuropsychological test outcomes (probiotic and prebiotic), hepatic encephalopathy outcomes (probiotic, prebiotic, and synbiotic), instant memory in patients with Alzheimer's disease (probiotic), depressive symptoms (probiotic, prebiotic and synbiotic), mood states and psychiatric distress (probiotic), overall mental health (probiotic), neurological function (probiotic), brain-derived neurotrophic factor (BDNF) concentration (probiotic and synbiotic), and Pittsburgh Sleep Quality Index (PSQI) score (probiotic). All three are similar in that the intake of probiotics, prebiotics, and synbiotics might be associated with improvements in hepatic encephalopathy outcomes and depressive symptoms, both probiotic and synbiotic intake might be associated with elevated BDNF concentrations, and both probiotic and prebiotic intake might be associated with improved neuropsychological test results. The difference between the three is that the neuropsychiatric effects of probiotics might be more widespread and be reflected in the fact that probiotic intake might also be associated with improvements in mood states and psychiatric distress, overall mental health, neurological function, Alzheimer's disease patients' instant memory, and PSQI score. Probiotics might be the best and most promising option for improving neuropsychiatric outcomes. In the future, in addition to requiring more high-quality meta-analyses, further preclinical studies are needed to explore specific relevant mechanisms and determine true causal relationships.