The duration of preoperative fasting may vary depending on the type of surgery and the patient’s body condition, and cannot be generalized. Generally, for minor surgery with local anesthesia, fasting and water fasting are not necessary before surgery. For general anesthesia surgery, the fasting time is about 8-12 hours before surgery, and the water fasting time is about 4 hours before surgery to prevent misaspiration caused by vomiting and reflux, or even respiratory failure. In addition, patients undergoing gastrointestinal surgery should fast 24-48 hours prior to surgery, with patients with pyloric obstruction generally requiring gastric lavage prior to surgery. For other gastrointestinal surgeries, enemas can be performed the day before surgery depending on the patient’s specific situation. Due to the different emptying function of gastric contents, the duration of preoperative water fasting should be adjusted as appropriate according to the patient’s own specific situation. Patients should follow the doctor’s arrangement before surgery and should not eat or drink privately because of hunger, and try not to eat too greasy food before surgery.