Saccharina Japonica Polysaccharides Suppress High‐Fat Diet‐Induced Obesity and Modulate Gut Microbiota Composition and Function

Recent studies have highlighted the potential of Saccharina japonica Polysaccharides (SJPs) in alleviating high‐fat diet (HFD)‐induced obesity by regulating gut microbiota, which warrants further exploration to elucidate the underlying structure‐activity relationship. In this study, five polysaccharide fractions (Sj‐T, Sj‐T‐1, Sj‐T‐2, Sj‐T‐3, and Sj‐T‐4) with different structure characteristics were prepared from S. japonica, and their effects on HFD‐induced obesity and gut microbiota composition were investigated using C57BL/6J mice. The results revealed that oral administration of Sj‐T considerably suppressed HFD‐induced obesity, glucose metabolic dysfunction, and other disordered symptoms. While, Sj‐T‐2, which has the lowest molecular weight, was the most effective in alleviating HFD‐induced obesity and had the second‐best effect on improving HFD‐induced impaired glucose tolerance among the five SJPs. Supplementation with SJPs significantly modulated HFD‐induced gut microbiota dysbiosis both at the phylum and species levels, such as enriching Desulfobacterota and Actinobacteriota, while suppressing the abundance of Bacteroidota. Sj‐T also dramatically restored the gut microbiota composition by modulating the abundance of many crucial gut bacterial taxa, including s_Bacteroides_acidifaciens, s_Lachnospiraceae _bacterium, and g_Lachnospiraceae_NK4A136_group. Besides, SJPs also dramatically altered the function of gut microbiota, including many carbohydrate‐metabolism enzymes. This study highlights the potential of SJPs in preventing obesity and restoring intestinal homeostasis in obese individuals.