Provided is a pharmaceutical or dietetic product, which serves for reducingand/or blocking the adhesion of pathogenic substances and organisms toeucaryontic cells, in particular mammal cells. Said preparation contains atleastone carbohydrate having an uronic acid unit on one of the ends thereof. 10 to100 % of the present, terminal uronic acid units pertaining to thecarbohydratesare provided with a double bond that is especially situated between the C4 andC5 atom.