Fucoxanthin, a marine carotenoid with diverse bioactivities, has attracted increasing attention for its health-promoting potential. However, its gastrointestinal fate and targeted delivery remain insufficiently understood, limiting its translation into effective applications. This review summarizes current knowledge on fucoxanthin's digestion, biotransformation, tissue distribution, interactions with the gut microbiota, and different delivery systems. In vivo, fucoxanthin is hydrolyzed to fucoxanthinol in the intestine and further converted to amarouciaxanthin A in the liver, undergoing subsequent dehydrogenation, isomerization, and esterification before distribution into plasma, liver, adipose tissue, and heart. Additionally, fucoxanthin modulates gut microbial composition through a duplibiotic effect, linking its metabolism to host-microbiota interactions. Lipid-, polysaccharide-, and protein-based delivery systems have been developed due to low oral bioavailability; these are also compared and summarized. Together, this review provides a theoretical framework for the rational design of functional foods and therapeutic applications of fucoxanthin.

Keywords: bioavailability; delivery system; fucoxanthin; gut microbiota; metabolism.