Psychobiotics were previously defined as live bacteria (probiotics) which, when ingested, confer mental health benefits through interactions with commensal gut bacteria. We expand this definition to encompass prebiotics, which enhance the growth of beneficial gut bacteria. We review probiotic and prebiotic effects on emotional, cognitive, systemic, and neural variables relevant to health and disease. We discuss gut–brain signalling mechanisms enabling psychobiotic effects, such as metabolite production. Overall, knowledge of how the microbiome responds to exogenous influence remains limited. We tabulate several important research questions and issues, exploration of which will generate both mechanistic insights and facilitate future psychobiotic development. We suggest the definition of psychobiotics be expanded beyond probiotics and prebiotics to include other means of influencing the microbiome.
Prebiotics and probiotics can influence the brain by communicating with the gut through the gut-brain axis (mainly the Vagus nerve), which is also known as psychobiotics. Psychobiotics also are responsible for neurotransmitter formation, which influences emotions and mental ability. This study is has some limitations, however, it shows the relationship between gut health and overall mental health.
To read more: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5102282/