The causes of diarrhea when drinking soup include greasy soup, irritable bowel syndrome, ulcerative colitis, allergies, etc. 1. Greasy soup: If the soup is very greasy, the intestines cannot fully digest the greasy food after drinking soup, thus causing diarrhea. 2. Irritable bowel syndrome: If the intestinal spasm is triggered by various factors, the digestive function of the intestines will be weakened at this time, so it will also cause symptoms of diarrhea. 3. Ulcerative colitis: due to various factors caused by intestinal damage, the intestinal digestive function decreases, at this time there will also be dilute phenomenon. 4. Allergy: when the patient is allergic to certain substances in the soup, drinking the soup can trigger an allergic reaction, resulting in diarrhea. Finally, if you have diarrhea after drinking soup, please consult a doctor in time.