Compositions for improving the health of a subject comprise alpha-(1,2)-branched alpha-(1,6) oligodextrans, preferably with an average molecular weight between about 10 kDa and 70 kDa, between about 10% and 50% alpha-(1,2)-osidic side chains, and having at least partial indigestibility in the subject. Methods for improving the health of a subject comprise administering the composition to a subject in an amount effective to improve gut health, or to prevent or treat a gastrointestinal disorder, a cholesterol-related disorder, diabetes, or obesity. Methods for making oligodextrans having controlled size and controlled degree of branching comprise providing alpha-(1,6) oligodextrans having an average molecular weight between 0.5 and 100 kDa and introducing at least 10% alpha-(1,2)-osidic side chains onto the alpha-(1,6) oligodextrans.