An exopolysaccharide-rich fraction from Bifidobacterium animalis subsp. lactis MG741 ameliorates high-fat diet–induced MASLD by enhancing intestinal barrier function

Exopolysaccharides (EPSs) produced by microorganisms have attracted interest as bioactive biopolymers, yet their roles in metabolic dysfunction-associated steatotic liver disease (MASLD) remain incompletely understood. Here, we prepared an EPS-rich fraction from Bifidobacterium animalis subsp. lactis MG741 (EPS-BL) by ethanol precipitation and dialysis, characterized its major molecular features, and evaluated its prebiotic and barrier-supporting activities in vitro and in a high-fat diet (HFD)-induced MASLD mouse model. EPS-BL was a mannose-dominant carbohydrate-rich preparation (219.38 mg/g mannose; weight-average molecular weight, 58.3 kDa) that also contained substantial protein, and should therefore be interpreted as a minimally processed EPS-rich material rather than a fully purified polysaccharide. In vitro , EPS-BL promoted the growth of L. plantarum and L. rhamnosus and upregulated mucin-related genes (MUC2 and MUC5AC) in LS174T goblet cells. In vivo , oral administration of EPS-BL (5 or 20 mg/kg, 8 weeks) reduced weight gain and fat mass, improved glucose-related indices, lowered circulating endotoxin, and ameliorated colonic and hepatic abnormalities in HFD-fed mice. EPS-BL also attenuated hepatic triglyceride accumulation, accompanied by suppression of lipogenesis-related proteins. Targeted metabolomics revealed coordinated shifts in serum and fecal metabolites associated with metabolic dysfunction biomarkers. Overall, EPS-BL mitigates HFD-induced MASLD in association with reinforcement of the gut barrier and modulation of the gut–liver metabolic axis, supporting its potential as a functional prebiotic ingredient. • EPS-BL is a bifidobacterial exopolysaccharide with a defined composition and moderate molecular weight. • Promotes beneficial lactobacilli and enhances goblet cell mucin secretion, reinforcing the mucus barrier • Lowers circulating endotoxin and improves glycaemic control and insulin sensitivity in HFD-fed mice • Suppresses hepatic lipogenic program (FAS/ACC/SCD1/ChREBP) and reduces triglyceride deposition • Targeted metabolomics shows systemic and luminal metabolic rebalancing consistent with disease mitigation.