Dyspepsia after eating may be a symptom of rectal cancer, and it may also be related to indigestion, irritable bowel syndrome, gastroenteritis and so on. 1. Rectal cancer: it belongs to a kind of malignant tumor, the cause of which is still unclear and may be related to environment, diet and genetic factors. Rectal cancer patients are prone to frequent bowel movements, change of bowel habit, urgency (discomfort in lower abdomen, wanting to defecate, feeling of incomplete defecation after defecation), blood in stool, abdominal pain, abdominal distension, etc. They may also have diarrhea after eating. However, there is no need to be too nervous, if necessary, need to do enteroscopy to further clarify the cause of the disease. 2. Dyspepsia: some people with dyspepsia may have diarrhea after eating due to gastrointestinal dyskinesia, decreased gastric tolerance and diastolic function of the stomach to the food, etc. Some people with dyspepsia also tend to have diarrhea after eating. Some people with dyspepsia are also prone to postprandial fullness, mid-upper abdominal pain, poor concentration and other symptoms. 3. Irritable bowel syndrome: the cause of irritable bowel syndrome is not clear, may be related to visceral hypersensitivity, abnormal gastrointestinal dynamics, intestinal infections and other factors. Typical symptoms of patients include abdominal pain, diarrhea, constipation, heartburn, etc., which can be manifested as diarrhea after eating. 4. Gastroenteritis: Gastroenteritis is related to viral, bacterial and other pathogenic microbial infections, and digestive reflux, intestinal flora imbalance. Patients are prone to epigastric pain, diarrhea, abdominal distension, postprandial fullness, loss of appetite, belching (hiccups) and other symptoms, and some patients may have diarrhea after eating. It is recommended that those who have diarrhea after eating should consult a doctor for examination in order to clarify the cause of the disease and then follow the doctor’s instructions for treatment.