Abstract The gut microbiome, often referred to as the “second brain,” plays a central role in the bidirectional communication network known as the gut–brain axis. Microbial signals travel via the vagus nerve, influencing mood and cognition. Animal studies demonstrate that probiotic effects on behavior are abolished when the vagus nerve is severed, highlighting its importance in gut–brain communication. Gut bacteria also synthesize key neurotransmitters, including 90–95% of the body’s serotonin, as well as GABA and dopamine. Furthermore, the fermentation of dietary fiber generates short-chain fatty acids (SCFAs) that strengthen the blood–brain barrier and reduce neuroinflammation. Dysbiosis can lead to "leaky gut," allowing inflammatory markers to trigger neuroinflammation linked to emotional instability. Restoring microbiome diversity through dietary intervention may represent a novel therapeutic pathway for mood disorders.
Tanushree Shah (Mon,) studied this question.