The residence time of food residue in the intestines is usually about 20 to 40 hours, but the exact residence time is related to the individual’s ability to digest and absorb, and will fluctuate slightly. It usually takes 24 to 48 hours for food to be excreted from the mouth to the formation of stool. Food generally stays in the stomach for 4 to 6 hours, then empties through the stomach into the small intestine for digestion and absorption, and then finally enters the colon for reabsorption of water and electrolytes to form feces, which is then excreted from the body. Generally food residue stays in the intestines for 20 to 40 hours. However, if the patient consumes some easy-to-digest food, such as rice porridge, pasta, etc., or takes laxatives, the food residue in the intestines will stay for a shorter period of time; if the patient has constipation, intestinal obstruction and other diseases, the retention time will be correspondingly longer. If the patient has no bowel movement for a long time, he needs to go to the hospital in time.