Why do I need to fast before surgery?


If you are about to undergo surgery, it is often required or recommended to fast beforehand. This means you can’t eat or drink. But why? What are the implications and what happens if you do eat it?

Protecting the respiratory tract

During surgery, your stomach should be empty. If there is food in there, stomach acid will be produced. As you are under anesthesia during the operation, many normal body reflexes, such as coughing and swallowing, are temporarily disabled. Without a swallowing reflex, the acidic contents of the stomach can flow into the airways. In the worst case, this can lead to choking. The less content there is in your stomach, the lower the risk of gastric juice reflux. During normal sleep, you do not run this risk, because it is a natural reflex of your trachea to close to the gastric contents that have been expelled.

It is therefore required to fast before any form of anesthesia, including loco-regional anesthesia (epidural or arm or leg anesthesia).

Duration of the fast before the surgical procedure

The usual advice is not to eat anything 12 hours before the surgery. If your operation is scheduled for the afternoon, a light breakfast – up to six hours before the procedure – is usually not a problem. However, it is advisable to check with the anesthesiologist or the clinic for a precise recommendation.

You can drink the following clear fluids up to two hours before the time of admission:

  • Non-gaseous liquids (including energy drinks)
  • Tea without milk
  • Black coffee without milk
  • Fruit juice without pulp (for example, apple juice)

From two hours before your admission, you can no longer drink anything, except for a sip of water to take medication.

Staying fasting, but not too long

While fasting is almost always necessary before surgery, you don’t need to stay hungry longer than necessary. 12 hours of fasting before the operation is often enough. You should also avoid dehydrating yourself before the surgical procedure for no valid reason. Please talk to your doctor for his an appropriate recommendation.

Furthermore, a long fast is not conducive to post-operative recovery. Indeed, excessive fasting can affect insulin sensitivity and inhibit all kinds of important physical processes for convalescence.