Spicy Food Intake and Dietary Factors Shape the Gut Microbiome and Metabolism of Mucin and Short-Chain Fatty Acids in Healthy Adults

The intestinal mucus layer provides a primary barrier between the gut microbiota and the epithelium. Capsaicin, a major component of spicy foods, has been reported to enhance muc2 expression and mucus secretion; however, evidence from preclinical and clinical studies remains inconsistent. How spicy food interacts with external factors such as alcohol to influence mucus-layer homeostasis also remains insufficiently understood. Using shotgun metagenomics, we investigated the associations between spicy food intake, alcohol consumption, intestinal fatty acid–binding protein (I-FABP), liver fatty acid–binding protein (L-FABP), gut microbial composition, and functional pathways in 229 healthy Korean adults. Alcohol intake was positively correlated with urinary I-FABP (ρ = 0.26), indicating mild epithelial stress, whereas spicy food intake was not associated with either FABP biomarker. Individuals who consumed highly spicy food exhibited an increased abundance of short-chain fatty acids (SCFA)-producing and mucin-metabolizing taxa, including Blautia , Coprococcus , and Ruminococcus , along with higher activity of mucin-degradation and SCFA-production pathways. Individuals who consumed a high level of alcohol showed stronger enrichment of mucin-degrading taxa, with reduced SCFA flux and increased abundance of Proteobacteria and Fusobacteriota. Cross-classified dietary groups revealed distinct mucin and SCFA gene activity patterns. Notably, the DHSH group displayed concurrent elevation of mucin turnover and SCFA production with indications of dysbiosis. These findings suggest that spicy food may modulate mucus layer metabolism in a context-dependent manner, whereas alcohol more consistently perturbs mucin–SCFA networks and epithelial integrity.