Dietary polysaccharides and intestinal mucus barrier homeostasis: a glycan resource reallocation framework

Dietary polysaccharides are increasingly investigated as functional food components that modulate gut microbiota, microbial metabolites and epithelial barrier function, yet the intestinal mucus layer is less often examined as a glycan-centered ecological interface. Here, we evaluate a glycan resource reallocation framework in which structurally accessible, non-digestible or poorly digestible food polysaccharides expand the colonic exogenous-glycan pool, alter microbial access to dietary and host glycans, and may reduce excessive microbial reliance on host mucin O-glycans. We distinguish four evidence levels: barrier-associated markers, structural mucus readouts, functional mucus barrier measurements and direct glycan-flow validation. Current evidence strongly supports associations among dietary polysaccharides, microbial metabolism, inflammatory restraint and epithelial repair, whereas direct demonstration of carbon reallocation from mucin to dietary glycans remains uncommon. Polysaccharide structure, including linkage, branching, molecular size, charge and conformation, determines microbial accessibility and therefore patterns of microbial metabolism and host signaling. Human milk oligosaccharides are considered only as a boundary case because they are oligosaccharides rather than dietary polysaccharides, although their structural resemblance to mucin 2 (MUC2) glycans and their compatibility with stool-based MUC2 glycomics provide useful translational lessons. We propose that robust claims of mucus restoration should integrate MUC2/Muc2 production with mucin glycomics, mucus penetrability, bacterial–epithelial distance, glycan-utilization function and causal microbiota–metabolite testing.