LACTITOL IS A DISACCHARIDE DERIVATIVE CONSISTING OF GALACTOSE AND SORBITOL WHICH IS ONLY MINIMALLY ABSORBED AND IS NOT HYDROLYSED BY THE DISACCHARIDASES OF THE GASTROINTESTINAL TRACT AND THUS REACHES THE COLON UNCHANGED. IN THE COLON IT IS BROKEN DOWN TO SHORT CHAIN ORGANIC ACIDS, MAINLY ACETIC, PROPIONIC AND BUTYRIC ACID, BY THE INTESTINAL FLORA, IN PARTICULAR BY THE BACTEROIDES AND LACTOBACILLI, THUS ACIDIFYING THE CONTENTS OF THE COLON. THE EFFECT OF THIS ACIDIFICATION IS TO REDUCE THE ABSORPTION OF AMMONIA. THE TRANSFORMATION OF LACTITOL INTO LOW MOLECULAR WEIGHT ORGANIC ACIDS RESULTS IN AN INCREASE IN OSMOTIC PRESSURE IN THE COLON, THEREBY CAUSING AN INCREASE IN THE STOOL WATER CONTENT AND STOOL VOLUME WHICH EXPLAINS THE LAXATIVE EFFECT.