Why Do People Fast before Surgery?

If you’re having surgery under general anesthetic, your physician will tell you not to eat for at least 6 hours before the surgery (but possibly a lot longer) and not to drink for at least 2 hours before the surgery. Why is this? When you go under general anesthetic, your body loses tonus (the continuous low-level activity of tissues like muscles) meaning that the contractions that keep food moving through the digestive system stop. You may know of this movement as peristalsis. Without this movement, your body can react to any solids or liquids in your stomach with a vomiting reflex, which could result in food or drink getting into your lungs and even causing damage.

Always check with your physician how long you should avoid solid foods and fluids before an operation. Even if you’re not having general anesthetic, there may be reasons to fast.

What about Eating after Surgery?

Naturally, having fasted before surgery, you’ll start to feel hungry and thirsty some time afterwards, although not immediately! The body takes some time to want to eat again. Within 1 to 3 days after you wake up from surgery, but most often on the same day, you’ll be asked to drink and eat some simple things: for example, water, weak tea, chicken or vegetable broth, or dry toast. Starting simple and small means your stomach and small intestine aren’t immediately overwhelmed!

It can happen that patients vomit after even this first little amount of food: That’s a sign that they haven’t regained enough tonus and peristalsis isn’t happening. Provided you don’t have this reaction, you’ll slowly be put back on a greater variety of foods.

Does Abdominal Surgery Complicate Matters?

Examples of abdominal surgery are exploratory surgeries like laparotomies, to diagnose internal bleeding and other injury; repair of hernias in the abdominal wall; removal of the appendix or gall bladder; and resection of part of the small or large intestine. Cesarean sections are also abdominal surgeries.

Abdominal surgery adds a complication to fasting before and eating after surgery, particularly intestinal surgery. It might require a longer period of fasting. You might have to drink something that helps flush solids out of your intestine. And after the surgery, your digestive system might need slightly longer to recover. It can take up to three days for some patients to be ready to eat solid food again.

There is evidence that it is safe to take food by mouth within 48 hours of even major abdominal surgery. There is proven to be a very low risk of the passage of simple foods bursting the stitching or affecting the surgical site. This is discussed in the paper “Postoperative Nutrition Management: Who Needs What?”, which talks about the Enhanced Recovery after Surgery protocol. Under a medical professional’s supervision, getting back to taking food by mouth within days of surgery is the preferred approach.

Be Aware of the Risk of a Caloric Gap

However, despite being safe, possible, and desirable, taking food by mouth might not be enough for a patient after their abdominal surgery. The paper mentions that oral feeding is often insufficient to meet the protein and energy requirements of the recovering patient. Protein deficiency can be due to the challenges of digesting protein-rich food after the surgery. A caloric gap (a negative difference between the calories that the body gets from food and the amount of energy it is using) is especially bad during recovery: A good prognosis requires a good nutritional status.

A caloric gap is most dangerous if the patient has a nutritional deficit going into the surgery. Preexisting malnutrition can occur in pregnant people who have had insufficient access to food, in cancer patients, and in people with gastric and intestinal disorders, among others. The referenced paper notes that patients are not always assessed for preexisting malnutrition and that this should be a standard part of the preoperative assessment.

The risk of needing follow-up surgery presents another challenge to patients getting enough protein and energy via oral feeding. Complications can occur after any surgery and re-operation will need further fasting and another period of adjustment before the patient can eat again.

What Is the Alternative to Taking Food by Mouth?

• Enteral feeding is one option. Also called tube feeding, it involves delivering liquid food directly to the stomach or small intestine through a tube that is inserted via the nose or through the skin and muscles of the abdomen.
• Parenteral feeding is another option. It can also be called intravenous feeding. A nutritional fluid is infused into the body through a vein. Enteral feeding is preferred to parenteral because it keeps the digestive system active. It is easier to transition to oral feeding from enteral feeding than from parenteral feeding.

Can Enteral Feeding Be Combined with Oral Feeding?

As explained in the paper “Postoperative Nutrition Management: Who Needs What?”, it is important for physicians to have a plan for postoperative nutrition in patients with preexisting malnutrition or other complications creating a protein or caloric gap. The recommendation of combining enteral and oral feeding is mentioned as a good way of preventing weight loss and other complications.

Talk to your physician prior to any surgery about any concerns you may have regarding your weight and nutritional status, fasting, and when you might be back on solid food. It’s important to have a full picture of how things might go.

Note: This post is based on an article that is not open-access; i.e., only the abstract is freely available. Furthermore, the authors of this paper make a declaration about lecture fees and research grants received from pharmaceutical companies. It is normal for authors to declare this in case it might be perceived as a conflict of interest.