The reasons for diarrhea involve a food intolerance as well as some less common factors. A person might be suffering from the allergy on certain food or beverages. Having a weak colon/bowel does not allow eating fried or heavy food like mushrooms. Diarrhea is often caused by the specific response of the organism to the prescribed medical treatment. Some drugs may cause diarrhea. Various types of infections may predetermine this problem as well. Finally, such types of surgery as a gallbladder surgery or stomach surgery might be the keys.