Polysaccharides from edible brown seaweed Undaria pinnatifida are effective against high-fat diet-induced obesity in mice through the modulation of intestinal microecology.

Brown seaweed is rich in polysaccharides including sulfated polysaccharides and alginate, both of which provide health benefits to the host but whose differences have not received sufficient attention. In this study, alginate from Undaria pinnatifida (UPA) and sulfated polysaccharides from U. pinnatifida (UPSP) were isolated, and their action was analyzed in high fat diet-fed mice. UPA and UPSP improved body composition, fat deposition in body tissues and organs, lipid abnormality and inflammatory response in mice, and compound polysaccharides from U. pinnatifida (UPP: UPA + UPSP) had a better effect on some physiological indexes, which could be attributed to the differences in the gut microbiota. Both UPSP and UPA modulated diet-induced microbiota dysbiosis, and UPP had better effect on changes in the gut microbiota, including an increase in Bacteroidales and reduction in both Clostridiales and Lactobacillales that had positive correlations with the improvement of the physiological status. The in vitro model of bacterial culture revealed that the use of Bacteroides on UPA and UPSP was species dependent, and UPP can better maintain the diversity and stability of the Bacteroidales community. This study indicated that polysaccharides from edible brown seaweed can benefit host health by improving the intestinal microecology, which can be helpful for the application of edible brown seaweed in health foods.