The usual rule is 6 hours for food and 2 hours for clear fluids.
NHS adult fasting guidance says do not eat for six hours before the anesthetic and keep clear fluids, such as water, squash without bits, or tea and coffee without milk, going until two hours before. Fasting exists because anesthesia switches off the reflexes that protect your airway; food in the stomach can be vomited and inhaled into the lungs, which is genuinely dangerous. Milk, milky coffee, and fizzy drinks count as food or are discouraged. Chewing gum, sucking sweets, and smoking are out on the day. The NHS also stresses that if your team told you to fast, that instruction includes light snacks and sweets, and that water is sometimes allowed but only if your team says so.
What to do
Common questions
How long before surgery should I stop eating?
The standard rule for planned surgery under general anesthesia: stop eating 6 hours before and keep clear fluids going until 2 hours before. NHS fasting guidance for adults says no food for six hours before the anesthetic, while clear fluids, meaning water, squash without bits, or tea and coffee without milk, are allowed up to two hours before. Milk counts as food because it curdles in the stomach, and chewing gum, sweets, and smoking are off the table on the day. The reason is safety: anesthesia relaxes the reflexes that keep stomach contents out of your lungs, and a full stomach raises the risk of dangerous aspiration. Your hospital's own instructions override any general rule, so follow the letter or pre-assessment advice you were given exactly, and tell the team honestly if you ate or drank inside the window. If you take insulin or morning medicines, ask in advance what to do about them on surgery day.