This study tested the hypothesis that an increased branch density (i.e., the percentage of alpha-1,6-glucosidic linkage) in water-soluble, starch-related alpha-glucans leads to reduced glucose release by pancreatin and amyloglucosidase. Malto-oligosaccharides and phytoglycogens were structurally analyzed and compared for their susceptibility to the enzymes. Malto-oligosaccharides were prepared by subjecting starch to alpha-amylase and beta-amylase followed by ultrafiltration to enrich alpha-1,6-glucosidic linkages. The branch density of the oligosaccharide products reached up to 17%, determined by (1)H NMR. Phytoglycogens were extracted from six sweet corn lines, and analysis showed similar chain length distributions and a branch density range from 8.8 to 9.5%, as compared with 4.6% for normal corn starch and 5.7% for waxy corn starch. The digestion behavior of these alpha-glucans was correlated to branch density: Highly branched malto-oligosaccharides had much reduced glucose release as compared with starch, whereas the reduction of glucose release from phytoglycogen was relatively low. Particularly, the reduction of glucose release associated with enhanced branch density was caused by reduced hydrolysis by amyloglucosidase.