Why You Can't Eat or Drink Before Surgery

Person pouring a glass of water from a water bottle.

Eugenio Marongiu / Getty Images

You may have been told not to eat or drink for eight to 12 hours before surgery. And that's a firm rule: No food or drink means no food or drink.

Don't snack or take even a sip of water. If you do, your surgery may be canceled or postponed.

Many surgeries are scheduled for the early morning. This means most of your eight to 12 hour fast will be at night while you are asleep.

You can stop eating around dinner time the night before. Don't take anything by mouth from the time you wake up until your surgery is over.

Some procedures require a bowel prep. This is a process that removes food and stool from your digestive tract. In most cases, though, you will just have to avoid food and fluids after the specified time.

This article discusses some of the reasons why you can't eat or drink before surgery. It also offers suggestions for what to eat before you begin your fast.

Why No Food or Drink Before Surgery

There are many reasons why you should not eat before surgery. One major reason is because food in your stomach can cause serious problems when you're given anesthesia.  

why you can't eat or drink before surgery

Verywell / Brianna Gilmartin

Aspiration

Aspiration is when something you eat or drink goes down your airway. If this happens while you're awake, your body reacts. You may cough, gag, or even vomit. Eventually, you will get the substance out of your airway.

Under general anesthesia, you can't react to aspiration. This is because you are unconscious and your muscles are paralyzed. You aren't able to cough anything up.

You will also have a tube called an endotracheal tube in your throat. This tube helps you breathe but can make it easier to aspirate. It can also make it harder for medical staff to realize what is happening.

Aspiration can lead to aspiration pneumonia. This is a lung infection caused by inhaling foreign material.

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

Recap

You may aspirate food that's in your stomach when you are under general anesthesia. Under anesthesia, your body can not get rid of foreign substances in your lungs.

Nausea and Vomiting

Postoperative nausea and vomiting (PONV) is one of the most common complications of surgery. It is much easier to prevent than to treat and control after it starts.

You can avoid PONV if your stomach is empty when under anesthesia. There are drugs that can control nausea and vomiting, but it is far better to stop it from happening in the first place.

If you have food or fluid in your stomach while under anesthesia, you could vomit. You could aspirate the vomit into your lungs.

The best way to stop this from happening is to make sure your stomach is empty before surgery.

Your Bowel Prep Will Be Ruined

If there is food in your gastrointestinal (GI) system during GI surgery, it could complicate the surgery and lead to infection. If you eat or drink before GI surgery, your surgery may be canceled or rescheduled.

In some cases, bowel preparation is done before GI surgery. If you eat or drink after bowel preparation, it will undo everything you've done to empty your GI tract.

What to Eat Leading Up to Surgery

If you are several days or weeks from surgery, try to eat more lean, protein-rich foods. Examples include:

  • Pork
  • Chicken
  • Seafood
  • Tofu/beans
  • Low-fat dairy products

Protein can help you heal after surgery.

Hydrate, preferably with water. Your urine should be clear and mostly colorless. 

Drinking the right amount of water is something you should always try to do. Importantly, it can help you get through the fasting period before surgery. If you are well hydrated before you fast, you may feel less thirsty during your fast.

Recap

Eat lean protein and stay hydrated in the days leading up to your surgery. This will make it easier for you to get through the fasting period.

Your Last Meal Before Surgery

You may be tempted to have a huge meal before you start your fast. Unfortunately, this could defeat the purpose of fasting.

Instead, have a light meal like soup and salad. A heavy meal takes longer to digest.

Your surgeon may tell you to take your regular medications on the morning of your surgery. If so, plan to do so with the smallest sip of water possible. Do not take your medication if the surgeon does not say you should.

If you are unsure, call the doctor's office and ask. Or, take your pills with you to the surgical center.

Also be sure not to swallow water when you brush your teeth.

Diabetes and Fasting for Surgery

Fasting may cause problems for some patients. This is particularly true if you have diabetes.

Ask your surgeon how to handle low blood sugar if it happens while you are fasting.

Evolving Guidelines

Originally, the eight- to 12-hour rule was an educated guess. It was based on how long it might take for the stomach to empty, with some extra time added to be sure.

In the last couple of decades, research has raised some interesting points. One study found that drinking clear fluids up to two hours before anesthesia actually led to the stomach being more empty than fasting.

As research continues, the guidelines may change. In the meantime, follow your surgeon's instructions on what to do in the hours before surgery.

Summary

Your surgeon will instruct you to avoid food and water for up to 12 hours before surgery.

Fasting before surgery helps prevent complications. This includes nausea and aspiration. Aspiration is when you inhale food or fluids that were in your stomach. It can lead to a serious lung infection. Eating or drinking before surgery will also undo any bowel prep you have done.

Before you begin your fast, eat lean proteins and stay hydrated. Your last meal before surgery should be something light, like soup or salad. If you have diabetes, ask your surgeon how to manage low blood sugar while fasting.

Future guidelines may change based on research, but always follow your surgeon's instructions. 

A Word From Verywell

It seems simple: Fasting before surgery prevents problems. It is simple, but a truly amazing number of patients do not follow these instructions.

The risks of eating and drinking before surgery are higher than you may think. It is important to avoid all food and drink at least eight hours before anesthesia. The alternative may be aspiration pneumonia or other serious complications.

Frequently Asked Questions

  • Can you chew gum before surgery?

    Avoid chewing gum 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.

    It shouldn't be enough to require canceling the procedure, but it is still discouraged for patients who will go under anesthesia.

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

    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. These can be hard for your body to break down and may increase inflammation.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Practice guidelines for preoperative fasting and the useof pharmacologic agents to reduce the risk of pulmonary aspiration: applicationto healthy patients undergoing elective procedures: an updated report by the American Society of Anesthesiologists Task Force on Preoperative Fasting andthe 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.

  4. Cleveland Clinic. Best ways to prepare yourself for surgery.

By Jennifer Whitlock, RN, MSN, FN
Jennifer Whitlock, RN, MSN, FNP-C, is a board-certified family nurse practitioner. She has experience in primary care and hospital medicine.