An improved method for making a p. vulgaris bean extract that results in an extract having high α-amylase inhibitory activity and low hemagglutinin activity. The method involves treating the beans to selectively denature the hemagglutinin. A p. vulgaris bean extract is provided, having high α-amylase inhibitory activity and low hemagglutinin activity. A treatment for diabetes or method for reducing blood glucose level is disclosed using the p. vulgaris bean extract disclosed herein.
