Mediterranean diet, gut microbiota, and intestinal barrier integrity: implications for digestive and systemic health

The Mediterranean diet has gained increasing attention for its effects on gut microbiota, microbial metabolism, intestinal barrier function, and related clinical outcomes. This narrative review critically synthesizes evidence from 51 publications identified through structured searches of PubMed/MEDLINE and Google Scholar, including human intervention studies, observational studies, systematic and narrative reviews, and selected preclinical studies. The available evidence suggests that the MD can influence microbial composition and function, although taxonomic responses vary considerably between populations and study designs. More consistent findings involve microbial metabolic activity, particularly short-chain fatty acid production, bile acid remodeling, and polyphenol-derived metabolites. These changes may contribute to intestinal barrier regulation, mucosal homeostasis, and immune modulation. Human intervention studies provide supportive evidence in inflammatory bowel disease, functional gastrointestinal disorders, obesity, metabolic syndrome, and related conditions, while evidence for neurological, autoimmune, and cancer-related outcomes remains more limited and is often observational or mechanistic. Direct evidence for improved intestinal barrier function is still less extensive than indirect evidence based on inflammatory markers, microbial metabolites, and permeability-related measures. Differences in microbiome methodology, baseline diet, disease status, geographic background, and intervention duration contribute to variability across studies. The MD therefore represents a promising dietary framework for modulating gut microbial function and intestinal homeostasis, but further long-term and mechanistically integrated human studies are needed to define causal pathways and identify individuals most likely to benefit.