Extract obtainable by extraction from Phaseolus sp. with mixtures of ethanoland water, characterised by an .alpha.-amylase inhibitor content in between1,000 and 1,600 USP/mg (HPLC titre between 6 and 14% w/w) and aphytohaemagglutinin content in between 8,000 and 30,000 HAU/g, and a processfor its preparation.