Curcumin in inflammatory bowel disease: highlighting gut microbiota-metabolite-host interactions.

Inflammatory bowel disease (IBD) is driven by a complex interplay among epithelial barrier breakdown, immune dysregulation, microbial dysbiosis, and redox imbalance. Curcumin, a major curcuminoid from turmeric (Curcuma longa L.) and a widely used food ingredient, has attracted sustained interest as a dietary bioactive for IBD prevention and adjunct management. Notably, curcumin shows low systemic bioavailability, allowing a substantial fraction to reach the distal gut, where it can be biotransformed by the gut microbiota and act locally on the mucosa. This review synthesises recent evidence on: (i) curcumin's gastrointestinal fate, including host conjugation and microbial reduction to more stable metabolites; (ii) the bidirectional curcumin-microbiota relationship, whereby baseline microbial functions shape curcumin metabolism and response, while curcumin remodels microbial ecology and metabolite outputs (short-chain fatty acids, bile acids and tryptophan-derived indoles); and (iii) downstream host pathways linked to barrier integrity, NF-κB and MAPK signalling, immune cell polarisation, and redox-sensitive programmes (Nrf2 and ferroptosis susceptibility). We further discuss food-grade formulation and delivery strategies that tune colonic exposure and microbiota engagement, and outline research priorities for evidence mapping, responder stratification and standardised biomarkers to accelerate translation of curcumin-based functional foods for IBD.