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