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If you’ve had surgery under anesthesia, you know you need to fast — abstain from eating and drinking — beforehand. This advice isn’t arbitrary; it’s there to protect you.

Preoperative fasting reduces the risk of pulmonary aspiration, a severe condition that can lead to life-threatening complications.

Learn more about pre-surgery fasting, including myths and facts about why it’s necessary and current anesthesia fasting guidelines.

Why Do I Have to Fast Before Anesthesia?

Fasting before anesthesia reduces the risk of pulmonary aspiration. This condition occurs when your stomach contents end up in your airway (trachea) by accident.

Anesthesia and deep sedation affect your body’s ability to protect the airway. That puts you at a higher risk of what’s in your stomach aspirating into your airway.

Pulmonary aspiration can lead to complications like aspiration pneumonia. This is a potentially life-threatening bacterial lung infection that occurs when stomach contents enter the lungs.

While other factors can also affect pulmonary aspiration risk, your stomach contents play a large part. That’s why pre-surgery instructions include fasting.

Fasting before anesthesia decreases your stomach contents and stomach acid levels. In doing so, it reduces your risk of pulmonary aspiration. Fasting also lowers the risk of nausea and vomiting during anesthesia, another aspiration risk.

How Long Do I Need to Fast Before Surgery?

The American Society of Anesthesiologists Task Force updated its recommendations for preoperative fasting. The following are the updated pre-op fasting guidelines:

• Breastfed babies can nurse until four hours before surgery.
• Formula-fed babies can consume formula until six hours before surgery.
• You can and should consume clear liquids for up to two hours before your scheduled surgery time.
• You can consume solid foods and non-clear liquids until six hours before your scheduled surgery time.
• You should stop eating fried and fatty foods and meat eight hours before surgery.

It’s important to note that these are general fasting recommendations. Other health factors — such as diabetes, obesity, and pregnancy — can cause your stomach to empty more slowly.

Your surgical team may give you different recommendations based on your individual risk factors. Make sure to follow what they tell you.

What Happens If I Don’t Follow the Fasting Recommendations?

If you don’t follow the fasting recommendations, it raises the risk of anesthesia-related complications like pulmonary aspiration.

Your surgical team may choose to delay your surgery, especially if you’re scheduled for an elective procedure.

It isn’t always possible to follow the fasting guidelines for emergency surgeries. In those cases, your team will consider the risks of continuing with the procedure or waiting. If delaying the procedure is riskier, they’ll proceed.

Should I Fast Longer Than the Recommendations?

You shouldn’t have to fast longer than the preoperative fasting recommendations. In fact, fasting for too long can cause problems of its own after surgery. Potential complications from excessive fasting include:

• Anxiety.
• Dehydration.
• Headache.
• Hypotension (low blood pressure) when you receive anesthesia.
• Increased hunger and thirst after surgery.
• Increased insulin resistance after surgery, which can lead to poor wound healing.
• Nausea and vomiting after surgery.
• Tired or weak feeling.

People may also have longer hospital stays and recovery times.

Despite the potential harm, studies have shown that most people fast longer than needed before surgery.

A 2025 study in The Journal of Neonatal Surgery reported on 240 adults undergoing elective surgery. The study reported a median fasting time of 13.7 hours for solids and 9.2 hours for liquids. Only 18% of participants followed the recommended fasting guidelines.

A 2024 study in Cureus reported similar findings. The median fasting time for 306 elective surgery patients was 4.5 hours for liquids and 14.5 hours for solid food.

Frequently Asked Questions About Fasting Before Surgery

What does “NPO before surgery” mean?

NPO stands for the Latin phrase “nil per os.” In English, that means “nothing by mouth.”

“NPO before surgery” guidelines instruct you on when to stop eating and drinking before surgery.

Can I really have nothing to eat or drink after midnight?

No, you don’t have to stop eating and drinking at midnight. That comes from outdated advice.

According to a 2024 review article in BPA Open, “nothing after midnight” became standard in the mid-20th century. But more recent research has shown the potential harms of fasting for too long.

The current recommendations allow you to consume solid foods such as fruits, vegetables, juice with pulp, and non-clear, non-fatty liquids until six hours before surgery. You can consume clear liquids until two hours before surgery.

One possible exception: If you have an early-morning surgery, your surgical team may advise you not to eat after midnight. But drinking clear liquids should still be OK until two hours before surgery.

What clear liquids am I allowed to drink before surgery?

The following are examples of clear liquids you can drink until two hours before surgery:

• Black coffee or tea.
• Carbonated beverages.
• Fruit juices with no pulp.
• Lemonade/juice.
• Sports drinks.
• Water.

If you have questions about a specific drink, ask your surgical team for guidance.

Note: Alcohol is NOT a clear liquid.

How long before surgery can I drink water?

Because water is a clear liquid, you can drink it until two hours before surgery.

Is coffee or tea allowed before surgery?

Yes, you can drink coffee or tea until two hours before surgery. However, you should avoid using milk or creamers.

Do I need to stop taking my GLP-1 medication before surgery?

Glucagon-like peptide-1 (GLP-1) receptor agonists help treat conditions like diabetes and obesity. GLP-1 drugs can delay the amount of time it takes for your stomach to empty. This can increase the risk of pulmonary aspiration.

The American Society of Anesthesiologists released updated guidelines on GLP-1 use before surgery in 2024. The guidelines stress the importance of shared informed decision-making between you and the surgical team.

According to the guidelines:

• Most people can continue to take their GLP-1 medications before surgery.
• People at higher risk of aspiration may need to follow a 24-hour clear liquid diet before their surgery.
• In cases where there’s still a high risk of aspiration, you may need to temporarily stop taking GLP-1 drugs. Surgical teams should discuss the risks of stopping GLP-1s against the risks of continuing them.

You should discuss your use of GLP-1 drugs and other medications with your surgical team. They can give you specific recommendations.