Diarrhea after lunch may be related to irritable bowel syndrome, gastroenteritis, pancreatitis, intestinal tumors and other pathological factors, different factors are treated differently, generally oral norfloxacin, probiotic preparations and other drugs or surgical treatment. 1. Irritable Bowel Syndrome (IBS): Generally, there will be diarrhea after meals, the amount of stool is not much, it becomes paste containing some mucus, and there is usually no blood in the stool. Loperamide, probiotics and other medications should be used in this case. 2. Gastroenteritis: gastroenteritis gastric mucosa is damaged, when eating a greasy lunch, it will aggravate the stimulation of the gastrointestinal tract, accelerate gastrointestinal peristalsis, and diarrhea will occur, in this case, oral norfloxacin anti-infective treatment. 3. Pancreatitis: Fatty food will stimulate the pancreas, make pancreatic fluid secretion, leading to diarrhea, for the lunch is usually more fat content, so diarrhea will occur after eating, in this case, oral cefuroxime and other anti-infective treatments and pancreatic enzyme enteric-coated tablets to help digestion. 4. Intestinal tumors: Tumors in the intestines will make the intestinal function disorder, after eating lunch, it will aggravate the stimulation of intestines, and diarrhea reaction will occur. Generally this situation requires surgical treatment. All the above medicines should not be used by yourself, but should be applied under the guidance of doctor. If you have the symptom of diarrhea after lunch, it is recommended to go to the hospital and have regular treatment under the doctor’s guidance as soon as possible.