The Gut Microbiota–Polyphenol–NLRP3 Inflammasome Axis: A Key Regulatory Network Linking Diet to Chronic Inflammation

Background/Objectives: Chronic low-grade inflammation, underpinned by persistent activation of the NLRP3 inflammasome, is a central pathological mechanism in non-communicable diseases including cardiovascular disease, type 2 diabetes, inflammatory bowel disease, and neurodegeneration. Dietary polyphenols have been consistently associated with reduced inflammatory burden; however, the mechanisms underlying these effects remain incompletely understood. This review aims to characterize the gut microbiota–polyphenol–NLRP3 inflammasome axis as a central regulatory network through which diet modulates innate immune signaling and chronic inflammatory tone. Methods: A comprehensive narrative review of the available literature was conducted, integrating evidence from mechanistic studies in cell culture and animal models, microbiome research, metabolomics, and human epidemiological and interventional data. Results: The gut microbiota emerges as a critical biochemical intermediary that transforms dietary polyphenols into bioactive metabolites, including urolithins, phenyl-γ-valerolactones, protocatechuic acid, and short-chain fatty acids, with enhanced bioavailability and potent inflammasome-modulating properties. These compounds suppress NLRP3 activation through multiple converging mechanisms, including inhibition of NF-κB-dependent priming, mitochondrial quality control via mitophagy, Nrf2-mediated antioxidant responses, and HDAC inhibition. Evidence across cardiovascular, metabolic, neurological, and respiratory disease models supports the translational relevance of this axis. Conclusions: The microbiota–polyphenol–NLRP3 axis functions as an integrated, self-regulated network in which each component simultaneously shapes and is shaped by the others: dysbiosis primes NLRP3 and depletes protective metabolites, while inflammasome hyperactivation further destabilises microbial ecology; polyphenol biotransformation by specific taxa interrupts this feed-forward loop at multiple nodes, restoring homeostasis.