Fucoidan and galactooligosaccharides ameliorate high-fat diet-induced dyslipidemia in rats by modulating the gut microbiota and bile acid metabolism.

•Galactooligosaccharides (GOS) or fucoidan extracted from Undaria pinnatifida ameliorate high-fat diet–induced dyslipidemia, hepatic tissue steatosis, and aortic arch injury in Sprague-Dawley rats.•GOS significantly increased Verrucomicrobia, Bacteroidetes, Blautia, and Akkermansia, but decreased Firmicutes, and fucoidan significantly decreased Aerococcus and Actinobacteria.•Fucoidan and GOS increased the expression of cholesterol 7-alpha hydroxylase in liver and bile salt hydrolase (BSH) activity of small intestine contents.•According to Spearman analysis, Adlercreutzia and Oscillospira were positively correlated with BSH enzyme activity. Aerococcus and Brevibacterium were negatively correlated with BSH enzyme activity.•GOS and fucoidan supplementation supported Lactobacillus casei DM8121 growth and enhanced its BSH activity.