Sugar-free chocolate can act as a laxative if large amounts are consumed. This is due to the fact that sugar-free chocolate contains a sugar alcohol called Maltitol that ferments in the intestinal tract and attracts water. The resulting fermentation that attracts water can cause a laxative effect in the form of diarrhea and gas.
Other sugar substitutes in sugar-free chocolate, such as mannitol, sorbitol, isomalt and xylitol, can cause similar laxative effects. The intensity of the laxative effect caused by these sugar substitutes depends on the difference between each person's digestive tract and the amount consumed. According to the American Dietetic Association, if someone consumes more than 20 grams of mannitol or more than 50 grams of sorbitol in a day, he or she may experience diarrhea.