Fucoxanthin and the gut microbiota–organ axis: linking low bioavailability, microbial metabolites and multi-organ protection

Fucoxanthin is a marine carotenoid whose broad effects in experimental models contrast with its limited oral bioavailability. Human exposure to fucoxanthin-derived compounds varies with the food matrix and dosing regimen, with fucoxanthinol being the principal reported circulating metabolite. This review evaluates the proposed fucoxanthin-gut microbiota-organ framework across the gut-liver, gut-brain, and gut-lung axes, systemic metabolism, and tumor biology and immunity, distinguishing direct fucoxanthin evidence from mechanistic extrapolation and assessing dietary dose relevance. Animal studies associate fucoxanthin with microbiota remodeling, improved intestinal barrier function, and reduced lipopolysaccharide translocation. These alterations could influence short-chain fatty acid, bile acid, and tryptophan-derived metabolite signaling, although complete microbiota-metabolite-receptor pathways remain insufficiently validated. Fecal microbiota transplantation supports a microbial contribution to colorectal cancer protection in one mouse model, whereas gut-brain and gut-lung mechanisms remain largely inferential. Many nominal human-equivalent doses derived from animal studies exceed estimated dietary intakes, and cellular fucoxanthin concentrations often exceed circulating human fucoxanthinol concentrations. Human colonic exposure remains unquantified and cannot be inferred from plasma concentrations. Future studies should integrate causal models, luminal and systemic exposure measurements, targeted metabolomics, and human trials to establish the nutritional relevance of fucoxanthin.