Why Can’t I Eat Before Surgery?


If you’re having surgery on your shoulder, why does it matter what’s in your stomach? We asked Dr. Matthew Hoberg to explain more about pre-surgery directives, including fasting. 

If you have an upcoming surgery, your care team likely gave you instructions to fast before your procedure. But why? We asked Matthew Hoberg, M.D., medical director of Renown Surgical Services, to explain why it’s important to forgo food and drinks before surgery.

Why are patients instructed to fast before surgery?

Regardless of surgery type or site, we want the stomach to be empty before having anesthesia, because anesthesia can reduce your body’s ability to protect and prevent food or acids from the stomach from entering the lungs.

Normally, your body is able to prevent this, but anesthesia medicines make it harder for your body to do so. When food or liquids from the stomach get into the lungs, doctors call it “aspiration.” This is rare, but can be dangerous if it does happen.

Solid foods and liquids leave the stomach at different rates too. Solid food takes longer to empty from the stomach than liquids, so the time to stop eating solids (eight hours) is longer than that for clear liquids (two hours).


The body has energy reserves to produce needed nutrients and fuel during fasting. Recently, studies have shown it is important to stay hydrated and have some carbohydrates in clear liquids up to two hours before surgery, so clear liquids are allowed until two hours before surgery.

There are also special rules for babies and young children who need surgery. For example, you may give breast milk up to four hours before surgery. If your baby drinks formula, you should stop six hours before surgery, and all solid foods you should stop eight hours before. Your child’s doctor or nurse will give you exact instructions.

What if you show up for surgery and have broken the no-eating rule? Will surgery be re-scheduled?

If patients have not followed the fasting guidelines, surgery will be postponed or rescheduled due to the possible increased risk associated with not having an empty stomach. The exception would be emergency surgery that cannot be delayed in which case special precautions are taken to help prevent anything from getting into the lungs.

What other pre-operative rules should be followed to the letter? 

All instructions given to patients before their surgery or procedure should be followed. There are specific medical reasons behind all the instructions and they are designed for safety —  to minimize risks, lower complications like infections and enhance the recovery process to help patients get back to normal as quickly as possible.

Also, many patients ask if they should continue taking medications before surgery. The answer is: It depends. Your doctor or nurse will tell you which medicines you should take and when. Some medicines need to be stopped before surgery. But for others, it’s important you keep taking them as usual. You may also get new medicines to take before surgery.

You may be asked to take some medications before surgery as part of advanced pain management protocols. If you need to take medicine right before your surgery, you can take it with a sip of water.


  1. I didn't realize that anesthesia could make it harder for your body to keep liquids out of your lungs, so having food in your stomach during surgery can cause you to choke and suffocate. My cousin needs to go in for surgery, so she's been wondering why she can't eat. I'll share this article with her, so she can understand.