Hi diarrhea is due to something in the diet that is taken in excess. Usually this is an excess of a sugar or chemical substance. Common examples are alcohol and caffeine. An excess of alcohol, especially beer and also Caffeine-containing drinks have a laxative potential. chronic unexplained diarrhea may be due to an infection with an intestinal parasite it could also be due to Lactose intolerance - elimination of all lactose-containing products from the diet would help to overcome..