Method of making a material with a high content of secoisolariciresinol diglycoside (SDG) comprises extracting a plant material with a high content of SDG using a basic alcohol. Independent claims are also included for: (1) a high-SGM material obtained by the method; (2) a foodstuff or beverage ingredient comprising (1); (3) foodstuffs and beverages containing (2); and (4) a foodstuff or beverage containing SDG and isoflavone.