High amylose flour may be processed by a short hydrothermal treatment to increase its total dietary fiber (TDF) content. These flours may be prepared by heating a high amylose flour at a total water content of from about 10 to 50% by weight at a temperature of from about 80 to 160.degree. C., for about 0.5 to 15 minutes at target temperature. This invention further relates to products which contain the high TDF flour, including food products.