CDF was more effective than DSW or fucoidan alone in improving blood glucose, lipid levels, and histopathological changes in T2DM rats. CDF also enhanced the phosphorylation of Akt and GSK3β, which are important steps in insulin signaling. Fecal metabolomics and 16S rDNA analysis showed that CDF altered the composition of gut microbiota and metabolic pathways. Here, GSK3B is linked to type 2 diabetes mellitus.