Patients are asked not to eat or drink before surgery to minimize the risk of a pulmonary aspiration. This is when contents in the stomach, including food, drink, and vomit, are expelled into the lungs. Aspirations block the airway and cause significant damage; sometimes, they can be fatal.
Historically, anesthesiologists have banned patients from eating or drinking anywhere from eight to 12 hours before surgery. Now, many say this practice is overprotective. Patients should confirm with their doctors how long they should abstain from eating or drinking before an operation.