Dietary carboxymethyl starch improves glycemic control and enhances barrier function via Bifidobacterium-mediated galactose metabolism in vivo and in organoids.

Etherified resistant starches (ERS), including hydroxypropyl starch (HPS), carboxymethyl starch (CMS), and hydroxyethyl starch (HES), are emerging as functional food ingredients with potential to modulate glycemic responses and gut health. However, their comparative efficacy and underlying gut-mediated mechanisms remain poorly defined. This study systematically evaluated their digestive properties and effects on gut microbiota. In vitro digestion demonstrated that etherification substantially increased resistant starch content, with CMS exhibiting approximately 70% resistant starch content and the lowest estimated glycemic index (GI = 53) among the tested starches. In vivo evaluation further showed that CMS significantly attenuated the peak postprandial glucose level (9.6 mmol/L) compared with native starch (17.4 mmol/L). Microbiome analysis revealed that CMS intervention was associated with specific remodeling of the gut microbiota, notably enriching beneficial Bifidobacterium pseudocatenulatum and Bifidobacterium adolescentis. Functionally, integrated KEGG pathway analysis and metabolomics consistently indicated that CMS markedly downregulated galactose metabolism, evidenced by reduced concentrations of galactose-related metabolites such as galactonic acid and galactitol. Furthermore, Spearman correlation analysis highlighted a strong mechanistic link between B. adolescentis abundance and galactose metabolic shifts. Crucially, utilizing, CMS-derived microbiota enhanced intestinal barrier function and galactose metabolism via co-culture model of gut microbiota and colonic organoids. Overall, CMS as a promising functional food ingredient that not only mitigates postprandial glycemia but also improves gut health by regulating microbiota-dependent galactose metabolism.