Butyrate-Producing Bacteria as a Keystone Species of the Gut Microbiome: A Systemic Review of Dietary Impact on Gut–Brain and Host Health

The human gut microbiome is a complex ecosystem integral to host health, with butyrate-producing bacteria (BPB) playing a critical role in maintaining intestinal homeostasis. This scoping review explores the composition, function, and systemic influence of BPB, focusing on their metabolic product, butyrate, and its implications for gut integrity, immune modulation, and gut-brain axis (GBA) communication. Disruptions to BPB abundance, which is correlated with Western dietary patterns, food additives, and antibiotic exposure, are linked to gut dysbiosis and associated with a wide spectrum of chronic diseases, including inflammatory bowel disease (IBD), obesity, type 2 diabetes, neurodegenerative disorders, and psychiatric conditions. Butyrate supports colonocyte energy metabolism, reinforces epithelial barrier function, regulates goblet cell mucus production, and exerts anti-inflammatory effects via histone deacetylase inhibition and G-protein-coupled receptor signaling. The depletion of BPB and the resultant butyrate deficiency may represent a unifying pathophysiological mechanism underlying these conditions. Therapeutic strategies that restore BPB populations and butyrate levels, such as prebiotics, dietary fiber, and microbiota-targeted interventions, hold promise for mitigating inflammation and enhancing systemic health through microbiome modulation.