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. Dyslipidemia is an important risk factor for cardiovascular diseases. Fucoidan (FUC) is a polysaccharide extracted from brown marine algae with various biological activities. Galactooligosaccharides (GOS) are important prebiotics that exert benefits on the intestinal microbiota. The aim of this study was to investigate the effects of FUC and GOS on dyslipidemia in rats by modulating the gut microbiota and bile acid metabolism. Twenty-four male inbred Sprague-Dawley (SD) rats aged 8 wk were fed a normal or high-fat diet (HFD) for 8 wk. During the feeding period, rats were gavaged with normal saline solution, FUC solution (100 mg/kg),or GOS solution (800 mg/kg), or a combination of both once daily. Serum biochemical parameters were determined, and the gut microbiota were analyzed via 16S rRNA gene sequencing. Bile salt hydrolase (BSH) activity in the small intestinal contents was also analyzed. The effects of FUC and GOS on Lactobacillus casei DM8121 were analyzed in vitro. In rats, GOS and FUC supplementation significantly improved serum total cholesterol, low-density lipoprotein cholesterol, lipopolysaccharide, serum total bile acid, hepatic tissue steatosis, aortic arch injury, gut microbiota, serum high-density lipoprotein cholesterol, cholesterol 7-alpha hydroxylase expression in the liver, and BSH activity in the small intestinal contents. In an in vitro experiment, GOS and FUC supplementation significantly increased L. casei DM8121’s BSH activity. In rats, FUC and GOS supplementation improved serum dyslipidemia, gut microbiota, BSH activity, and bile acid metabolism–related pathways. In vitro, GOS and FUC supplementation increas