Can We Modulate Our Second Brain and Its Metabolites to Change Our Mood? A Systematic Review on Efficacy, Mechanisms, and Future Directions of "Psychobiotics".

Psychobiotics, live microorganisms that provide mental health by interacting with the gut microbiota, are emerging as a promising therapeutic option for psychiatric and neurodevelopmental disorders. Their effectiveness in addressing conditions such as depression, anxiety, insomnia, stress, autism spectrum disorder (ASD), and eating disorders were examined through a comprehensive analysis of existing studies up to the first half of 2024, based on data from reliable electronic databases. We found that psychobiotics can significantly reduce symptoms of various psychiatric disorders by influencing neurotransmitter levels, regulating the hypothalamic-pituitary-adrenal (HPA) axis, and improving gut barrier function through short-chain fatty acids (SCFAs) and other metabolites. However, several limitations were identified, including inconsistent study methodologies, small sample sizes, and a lack of data on long-term safety. Addressing these limitations through rigorous research is essential for establishing standardized protocols and fully confirming the therapeutic potential of psychobiotics. In conclusion, psychobiotics show great promise as complementary treatments for mental health conditions, but continued research is necessary to refine their application and integrate them into clinical practice effectively.