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Fasting before surgery: the rules and the reasons

Why the team asks for an empty stomach, what the guidelines say about clear fluids and solid food, and what trials found about shorter fasts and carbohydrate drinks.

3 minute read6 sources, each checked word for wordLibrary checked October 18, 2026

In short

  • Fasting before anesthesia aims to reduce the amount and acidity of stomach contents, lowering the risk of regurgitation and aspiration.E1Strong1
  • European guidelines encourage clear fluids up to 2 hours before elective surgery and stop solid food 6 hours before.E2Good2
  • A Cochrane review found no evidence that a shorter fluid fast raises aspiration risk compared with nothing by mouth from midnight.E1Strong1
  • The surgical team sets each person's fasting times. The times on this page are what guidelines say in general.

How sure each claim is:E1StrongE2GoodOfficial textReviewWhat the grades mean

Why fast at all?

Fasting before general anesthesia aims to reduce the volume and acidity of what is in the stomach during surgery. This reduces the risk of regurgitation and aspiration (stomach contents getting into the lungs).E1Strong1

What do the guidelines say?

The European Society of Anaesthesiology encourages adults and children to drink clear fluids up to 2 hours before elective surgery, including cesarean section. All but one member of the group considered tea or coffee with a little milk to still be a clear fluid. A little milk meant up to about one fifth of the volume.E2Good2

It says solid food should stop 6 hours before elective surgery. But it says an operation should not be cancelled or delayed just because someone is chewing gum, sucking a hard candy or smoking right before anesthesia.E2Good2

It applies the same advice to people with obesity, reflux and diabetes, and to pregnant women not in labor.E2Good2

The American Society of Anesthesiologists updated its fasting guidelines in 2023. The update addresses carbohydrate-containing clear drinks (with or without protein), chewing gum, and how long children fast.E2Good3

Is fasting from midnight necessary?

A Cochrane review found no evidence that a shortened fluid fast increases the risk of aspiration, regurgitation or related harm compared with the standard nothing-by-mouth-from-midnight policy.E1Strong1

Letting patients drink water before surgery resulted in significantly lower stomach volumes.E1Strong1

What about carbohydrate drinks?

Enhanced recovery (ERAS) guidelines replaced overnight fasting with carbohydrate drinks 2 hours before surgery.Review4

A Cochrane review found carbohydrate drinks before surgery linked with a small reduction in hospital stay in adults, with no change in complication rates. Aspiration pneumonitis was not reported in any patient.E1Strong5

Do weight-loss and diabetes injections change this?

GLP-1 medicines such as semaglutide can leave food in the stomach despite fasting. This has its own guide: Medicines to discuss before surgery.Official text6

Questions you might bring to your anesthesia team

  1. Exactly when should eating and drinking stop before my procedure?
  2. Which drinks count as clear fluids, and is a carbohydrate drink part of the plan?
  3. Do any of my medicines change the fasting plan?
  4. What should happen with my morning medicines on the day of surgery?

Every claim in this guide was written from its sources and checked against them word for word. Its clinical review by Dr. Recio, a practicing nurse anesthesiologist (CRNA), is pending. This line changes when the review is done.

Sources

Each source opens on PubMed, DailyMed or the publisher's page. Under each one are the exact words from it that this page relies on, copied word for word and checked against the original.

  1. Preoperative fasting for adults to prevent perioperative complications. Brady M, Cochrane Database Syst Rev, 2003. E1Strong Systematic review
    The words this page rests on
    Fasting before general anaesthesia aims to reduce the volume and acidity of stomach contents during surgery, thus reducing the risk of regurgitation/aspiration.
    There was no evidence to suggest a shortened fluid fast results in an increased risk of aspiration, regurgitation or related morbidity compared with the standard 'nil by mouth from midnight' fasting policy. Permitting patients to drink water preoperatively resulted in significantly lower gastric volumes.
  2. Perioperative fasting in adults and children: guidelines from the European Society of Anaesthesiology. Smith I, Eur J Anaesthesiol, 2011. E2Good Guideline
    The words this page rests on
    The key recommendations are that adults and children should be encouraged to drink clear fluids up to 2 h before elective surgery (including caesarean section) and all but one member of the guidelines group consider that tea or coffee with milk added (up to about one fifth of the total volume) are still clear fluids.
    Solid food should be prohibited for 6 h before elective surgery in adults and children, although patients should not have their operation cancelled or delayed just because they are chewing gum, sucking a boiled sweet or smoking immediately prior to induction of anaesthesia.
    These recommendations also apply to patients with obesity, gastro-oesophageal reflux and diabetes and pregnant women not in labour.
  3. 2023 American Society of Anesthesiologists Practice Guidelines for Preoperative Fasting: Carbohydrate-containing Clear Liquids with or without Protein, Chewing Gum, and Pediatric Fasting Duration-A Modular Update of the 2017 American Society of Anesthesiologists Practice Guidelines for Preoperative Fasting. Joshi GP, Anesthesiology, 2023. E2Good Guideline
    The words this page rests on
    These practice guidelines are a modular update of the "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." The guidance focuses on topics not addressed in the previous guideline: ingestion of carbohydrate-containing clear liquids with or without protein, chewing gum, and pediatric fasting duration.
  4. Enhanced Recovery After Surgery: A Review. Ljungqvist O, JAMA Surg, 2017. Review Expert review
    The words this page rests on
    The ERAS Society, an international nonprofit professional society that promotes, develops, and implements ERAS programs, publishes updated guidelines for many operations, such as evidence-based modern care changes from overnight fasting to carbohydrate drinks 2 hours before surgery, minimally invasive approaches instead of large incisions, management of fluids to seek balance rather than large volumes of intravenous fluids, avoidance of or early removal of drains and tubes, early mobilization, and serving of drinks and food the day of the operation.
  5. Preoperative carbohydrate treatment for enhancing recovery after elective surgery. Smith MD, Cochrane Database Syst Rev, 2014. E1Strong Systematic review
    The words this page rests on
    Preoperative carbohydrate treatment was associated with a small reduction in length of hospital stay when compared with placebo or fasting in adult patients undergoing elective surgery. It was found that preoperative carbohydrate treatment did not increase or decrease postoperative complication rates when compared with placebo or fasting.
    Aspiration pneumonitis was not reported in any patients, regardless of treatment group allocation.
  6. OZEMPIC (semaglutide) injection, Prescribing Information. Novo Nordisk, 2026. Official text FDA label
    The words this page rests on
    There have been rare postmarketing reports of pulmonary aspiration in patients receiving GLP-1 receptor agonists undergoing elective surgeries or procedures requiring general anesthesia or deep sedation who had residual gastric contents despite reported adherence to preoperative fasting recommendations.