Why You Can't Eat or Drink Before Surgery

Person pouring a glass of water from a water bottle.

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If you are planning to have surgery you may have been told that you should not eat or drink for eight to 12 hours prior to your procedure. Unless you have been told that it is OK to take your medications the morning before surgery with a few sips of water, no food or drink truly means no food or drink.

That means absolutely no food or drink. Not a snack or even a sip of water, or your surgery may be canceled or postponed.

The good news is that most people sleep through most of the eight to 12 hour period of fasting before surgery as many surgeries are scheduled in the early morning. Patients may stop eating around dinnertime the night before surgery and then don't take anything by mouth from when they wake up until surgery is completed.

In some special cases, a bowel prep may be completed, which is a process that is used to remove food and stool from the digestive tract—but most patients are able to just avoid eating food after lunch or dinner.

Why No Food or Drink Before Surgery

There are multiple reasons why patients are asked not to eat prior to their procedure, some of which are potentially serious complications caused by having food in the stomach during the administration of anesthesia. 

why you can't eat or drink before surgery
Illustration by Brianna Gilmartin, Verywell


Have you ever taken a bite of something and had it "go down the wrong pipe?" That is aspiration. When it happens while you are awake, you cough, gag, maybe even vomit, but you get the food out of your airway. Aspiration can happen with saliva or the food and fluid you drink.

Under general anesthesia your ability to react is gone because your muscles are paralyzed and you are unconscious, so you cannot "cough it up." There is also a tube in your throat, called an endotracheal tube, which can make it easier to aspirate and harder for medical staff to realize it is happening.

While aspiration is most common during general anesthesia, it can also happen when a patient is sedated or too sick to protect their airway.

Your Bowel Prep Will Be Ruined

If your surgery will be in part of your gastrointestinal system, having food in your system could complicate the surgery and lead to infection. Eating or drinking prior to your procedure could cause the surgery to be canceled.

In some cases, bowel preparation is done, a process that completely empties your digestive tract to prepare for surgery. To eat or drink after your bowel preparation could undo all of your efforts to empty your digestive tract.

Nausea and Vomiting

Postoperative nausea and vomiting (PONV) is one of the most common complications of surgery and is far easier to prevent than to treat and control after it begins. While there are medications available to treat nausea and vomiting, the easiest way to prevent it is to have an empty stomach when anesthesia is provided.

Additionally, if you have food or fluid in your stomach during your surgery, you could vomit while under anesthesia. The combination of anesthesia, which paralyzes the body, and intubation makes it possible for you to inhale the vomit into your lungs.

Asleep and paralyzed, your ability to cough, or even to spit vomit out of your mouth, is taken away and the risk of aspiration is high. This aspirated food or fluid can quickly lead to aspiration pneumonia, a lung infection caused by inhaling foreign material.

The best way to prevent aspiration from happening is to make sure your stomach is empty before surgery.

Food Intake Leading Up to Surgery

If you are several days or weeks from surgery, try to make lean, protein-rich foods such as pork, chicken, seafood, or tofu/beans and low-fat dairy products a part of your diet. Protein is an essential part of the healing that takes place after surgery.

Hydrate, preferably with water, until your urine is clear and mostly colorless. You may be pleasantly surprised by how you feel when you drink an adequate or ample amount of water—those little aches and pains that you believe to be normal may go away entirely, and you may feel more energetic.

Eating and drinking well prior to your period of fasting will help you tolerate the process better, especially if you drink enough fluids to prevent significant thirst during your fast.

Your Last Meal Before Surgery

You may be tempted to have a huge meal before you start your eight- to 12-hour fast. Do not give in to the temptation, as it can completely defeat the purpose of fasting.

Instead, have a light meal such as soup and salad for your final meal before surgery. A heavier meal takes longer to digest and negates the effect of abstaining from food and drink prior to surgery.

If your surgeon has said you should take your regular medications on the morning of your surgery, plan to do so with the smallest sip of water possible. Do not take your medication if the surgeon has not instructed you to do so.

If you are unsure, call the doctor's office or take them with you to the surgical center. Also, take care not to swallow water when you brush your teeth.

Diabetes and Fasting for Surgery

For some patients, particularly those with diabetes, fasting can cause additional issues. Talk to your surgeon about how they would like you to handle low blood sugar issues should they happen during your period of fasting.

Evolving Guidelines

In the past, the eight- to 12-hour rule wasn't necessarily based in science but was more of an educated guess about how long it would take to empty the stomach fully with some additional time built in to be sure.

That said, research in the last decade has been more scientific and has produced some interesting results. One study even said that drinking clear fluids up to two hours before anesthesia actually led to the stomach being more empty than fasting.

At this time, most surgeons and anesthesia providers are still recommending a fast—refraining from both foods and fluids—of at least six hours prior to anesthesia.

As research continues, you can expect the guidelines for fasting to change based on clear evidence. In the meantime, your surgeon and anesthesia provider will give you clear instructions on what they want you to do in the hours before surgery.

Frequently Asked Questions

Can you chew gum before surgery?

You should avoid it if possible. The American Society of Anesthesiologists says that gum chewing can significantly increase the production of saliva and the volume of liquids in the stomach, but that it shouldn't be enough to have to cancel a surgery. However, they don't encourage gum chewing for patients undergoing procedures with anesthesia.

Are there foods you shouldn't eat in the days before surgery?

It's a good idea to eat healthy, nutrient-rich foods in the days before surgery. Choose fresh fruits and vegetables as much as possible. Avoid processed foods and red meats, since they can be difficult for your body to break down and may increase inflammation.

A Word From Verywell

It seems simple—don't eat before surgery to prevent problems. It is simple, but a truly amazing number of patients do not follow instructions when preparing for their surgery.

The risks of eating and drinking when you have been instructed not to do so are higher than you might imagine. It is important to avoid all food and drink at least eight hours prior to having anesthesia, as the alternative may be aspiration pneumonia or other serious complications after surgery if instructions are not followed.

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  1. Practice Guidelines for Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration: Application to Healthy Patients Undergoing Elective Procedures: An Updated Report by the American Society of Anesthesiologists Task Force on Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration. Anesthesiology. 2017;126(3):376-393. doi:10.1097/ALN.0000000000001452

  2. Maltby JR, Pytka S, Watson NC, Cowan RA, Fick GH. Drinking 300 mL of clear fluid two hours before surgery has no effect on gastric fluid volume and pH in fasting and non-fasting obese patients. Can J Anaesth. 2004;51(2):111-115. doi:10.1007/BF03018767

  3. American Society of Anesthesiologists. Chewing gum while fasting before surgery is safe, study finds. Published October 12, 2014.

  4. Cleveland Clinic. Best ways to prepare yourself for surgery. Published April 14, 2014.