Why Do Cats Have To Fast Before Surgery?

Fasting before surgery

Sometimes an image gives me an idea, and the photo below inspired this article. The photo below is of a cat who vomited after anesthesia and surgery and illustrates why veterinarians ask pet owners to withhold food for several hours before a scheduled surgery.

Why do cats have to fast before surgery?

General anesthesia is the administration of drugs or gas to render the cat unconscious. During anesthesia, the muscles relax, and the cat is unable to feel pain.

Cats who are due to have elective surgery will fast, usually from the night before. The cat can have his or her dinner, but no breakfast on the day of surgery. Water is usually left out two hours before the surgery is scheduled.

What is elective surgery?

Elective surgery is a term used for non-emergency surgery which is medically necessary, but can be delayed and includes:

  • Spaying and neutering
  • Dental work
  • Removal of benign tumours

Why can’t cats eat before surgery?

  • When a cat is put under general anesthesia, the gastrointestinal muscles and lower esophageal sphincter relax. This increases the risk of passive regurgitation of the stomach contents, which can enter the lungs due to the absence of upper airway reflexes (swallowing, coughing, or gagging), which are mechanisms to protect the airways.
  • Postoperative nausea and vomiting (PONV) is a common side effect of general anesthesia post-surgery. If the cat vomits during the post-operative recovery, it can aspirate into the lungs due to grogginess.

Aspiration of food, stomach acid, and fluids into the lungs can lead to inflammation or aspiration pneumonia, a life-threatening condition lung infection.


Not all cats can fast overnight, diabetics, senior cats, and young kittens are at increased risk of hypoglycemia (low blood sugar). Always check with your veterinarian for pre-surgery fasting based on your cat’s age and possible risk factors.

Fasting guidelines for cats before surgery

Protocols can vary from practice to practice, always speak to your veterinarian for their guidelines. The age, weight and health status of the cat are all factors in determining how long the cat should fast. The guidelines for diabetic cats and young kittens vary as fasting overnight can lead to dangerously low blood sugar levels.

Adult cats:

The American Animals Hospital Association (AAHA) recommendation for healthy adult cats is to withhold food for 4-6 hours.

Water can be left out overnight.


The American Animals Hospital Association recommendation for kittens under 8 weeks or under 2 kg are to withhold food for no longer than 1-2 hours.

Water can be left out overnight.

Diabetic cats:

The American Animals Hospital Association recommendation for fasting diabetic cats is to withhold food for 2-4 hours.

Water can be left out overnight.

What should you do if the cat has eaten?

Contact your veterinarian and let them know. They may choose to delay surgery to be on the safe side.

If you live in a multi-pet home and there is any risk of the cat getting into other pet’s food, put food out after the cat has been taken to the veterinarian or feed away from the cat scheduled for surgery. My Labrador was scheduled for ear surgery and there was a possibility she snuck some of the cat’s food the morning of surgery. We called the veterinarian, and although we couldn’t be 100% sure she had eaten, he decided to delay her surgery until the following week.

What if the cat needs emergency surgery?

It is not always possible to schedule surgery as emergencies can and do happen. The veterinarian may decide to delay surgery for several hours until the GI tract is empty. Sometimes the benefit of immediate surgery outweighs the risk of aspiration.

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  • Julia Wilson, 'Cat World' Founder

    Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio