This narrative review explores how substances produced by gut bacteria, known as microbial metabolites, may affect the brain. These include short-chain fatty acids, tryptophan metabolites, and bile acids. Under normal conditions, these substances act as messengers to help maintain a balanced immune system and protect the barrier between the blood and the brain.
When these gut metabolites become unbalanced, they may trigger immune issues and inflammation in the brain. The review suggests this process is linked to the progression of Alzheimer's disease, Parkinson's disease, major depressive disorder, and chronic insomnia. The research focuses on how the gut and brain communicate through these chemical signals.
Because this is a narrative review and not a clinical trial, the findings are not yet enough to change medical practice. The study highlights potential areas for future research, such as using fiber, prebiotics, or probiotics. These results are early and do not provide a direct treatment for these conditions.
