Optimizing Nutrient Intake Before Surgery: A Guide to Preparing Your Body

Optimizing nutrient intake before surgery means eating enough protein and overall food in the weeks beforehand, getting screened for malnutrition and anemia, and following your surgical team's exact instructions on fasting and any carbohydrate drink. It also means telling the team about every supplement you take, because some, including fish oil, vitamin E, ginkgo, garlic, ginseng, St. John's wort and kava, may need to be stopped, often about two weeks before the operation.

Evidence grade: Moderate. International guidelines (ERAS Society, ESPEN, ASER) base their pre-surgery nutrition advice on randomized trials, meta-analyses and large cohort studies, mostly in major abdominal surgery; the evidence for routine screening itself is rated low.

Why Nutrition Before Surgery Matters

Surgery puts the body under stress, and how well nourished you are going in affects how you come out. The ERAS Society's colorectal surgery guidelines note that malnutrition before surgery has been linked to more complications and higher mortality after surgery for gastrointestinal cancer, and that the risk of complications rises in people who have unintentionally lost 5 to 10% or more of their body weight [10]. A joint consensus from the American Society for Enhanced Recovery (ASER) and the Perioperative Quality Initiative calls poor nutritional status a strong independent predictor of poor outcomes after surgery [12].

The European Society for Clinical Nutrition and Metabolism (ESPEN) treats malnutrition and underfeeding as risk factors for complications. Its key principles include building nutrition into overall care, avoiding long periods of fasting before surgery, restarting eating as early as possible afterward, and starting nutrition therapy right away if a person turns out to be at nutritional risk [11].

Step 1: Get Screened for Malnutrition

The ASER consensus makes a strong recommendation for routine nutrition screening before surgery, to find people who need their nutrition improved first [12]. The ERAS guidelines agree that routine nutritional assessment should be offered, while noting there is no single agreed way to do it. Tools in use include the Nutritional Risk Screening score (NRS 2002), the Subjective Global Assessment and the Malnutrition Universal Screening Tool, and blood albumin may be part of the picture [10].

If you are found to be at risk, the ERAS recommendation is nutrition treatment, preferably by mouth, for at least 7 to 10 days before surgery. For malnourished patients, oral nutrition supplements started 7 to 10 days beforehand were associated with fewer infectious complications and fewer leaks where the bowel is rejoined [10]. Your team decides whether you need this and which product to use.

Ask about screening if you have lost weight without trying, have been eating poorly, or have a condition that affects digestion or appetite.

Step 2: Prioritize Protein and Regular Meals

The ASER consensus states that protein delivery is more important than total calorie delivery around the time of surgery, and that nutrition should restart immediately after surgery [12]. ESPEN adds early mobilization after surgery to help protein synthesis and muscle function [11].

In practical terms, the weeks before an elective operation are a good time to make sure every meal includes a protein food, such as fish, poultry, eggs, dairy, beans, lentils or tofu, and to avoid skipping meals. If your appetite is poor, smaller and more frequent meals may be easier. Our guide to protein intake for wound healing covers amounts and food choices in more detail.

Step 3: Check Iron and Anemia

Anemia is common before surgery. One large study cited in the ERAS guidelines found it in 31.1% of men and 26.5% of women having surgery. The guidelines say every cause of anemia, including iron deficiency and vitamin B12 or folate deficiency, should be investigated and corrected [10]. A blood test arranged by your team is the way to know. Do not start iron or other supplements on your own before surgery without asking, because your team may prefer a specific approach and timing.

For the nutrients most involved in healing, see our article on vitamins and minerals essential for post-surgical recovery.

Step 4: Follow Fasting and Carbohydrate Loading Instructions Exactly

Long overnight fasting is no longer the default in many hospitals. According to the ERAS colorectal guidelines, several randomized trials show that clear non-alcoholic fluids can be given safely up to 2 hours before elective procedures under anesthesia, and a light meal up to 6 hours before [10].

Some pathways also use a carbohydrate drink, sometimes called carbohydrate loading. In the protocol described by ERAS, patients drank 800 ml of a specially formulated carbohydrate drink the evening before surgery and 400 ml two to three hours before anesthesia, which has been shown to reduce the body's stress response to surgery [10]. This is not the same as eating a large pasta dinner or drinking juice.

These rules have important exceptions. ERAS advises that people with delayed stomach emptying and emergency patients should stay fasted overnight or for 6 hours, and it makes no recommendation on carbohydrate drinks for people with diabetes [10]. Fasting rules also vary by procedure and type of anesthesia. Follow the written instructions your surgical and anesthesia team gives you, even if they differ from what you read here.

Alcohol and smoking

The ERAS guidelines note that people who smoke have a higher risk of complications during and after surgery, and that drinking more than two units of alcohol a day increases the rate of infections after surgery [10]. If either applies to you, ask your team for support in the weeks before your operation.

Step 5: Review Every Supplement With Your Team

The American Society of Anesthesiologists (ASA) warns that some herbal and dietary supplements can prolong the effects of anesthesia, increase bleeding risk, raise blood pressure, interfere with other medicines or cause heart problems. It asks patients to list all supplements, including vitamins, to bring their bottles to the pre-surgery appointment, and notes that an anesthesiologist may recommend stopping supplements at least two weeks before the procedure [9]. The National Center for Complementary and Integrative Health (NCCIH) similarly advises telling your providers about all supplements as far in advance of an operation as possible [3].

This list is not complete, and the right timing depends on the procedure, your medicines and your health. Never stop a prescribed medicine, including a blood thinner, without instructions from the doctor who prescribed it. A standard multivitamin is unlikely to pose health risks [3], but list it anyway so your team has the full picture.

A Simple Pre-Surgery Food Plan

• Two to four weeks out: Ask about nutrition screening and blood tests if you have lost weight or eat poorly. Build each meal around a protein food plus vegetables, fruit and whole grains.
• Two weeks out: Bring your full supplement list or bottles to the pre-surgery visit and agree on what to stop and when.
• The week before: Keep meals regular. If your team prescribed an oral nutrition supplement, take it as directed.
• The day before and the morning of surgery: Follow the fasting and carbohydrate drink instructions exactly as written.
• After surgery: Eating usually restarts early in enhanced recovery pathways [11][12]. Our guide to managing digestion issues after an operation covers common problems in the first days.

Safety and Interactions

• Your surgical team has the final say. Fasting times, carbohydrate drinks, nutrition supplements and which products to stop all depend on your procedure and health.
• Bleeding risk: Fish oil at high doses, vitamin E, ginkgo, garlic and ginseng may affect bleeding [1][2][4][5][6][9]. This matters more if you take anticoagulants such as warfarin or antiplatelet medicines; talk to your doctor or pharmacist before surgery.
• Anesthesia: St. John's wort, kava and valerian may change how anesthesia works [9].
• Medicine interactions: St. John's wort can weaken many medicines [7]. Tell your pharmacist about every supplement.
• Diabetes: Ask specifically about carbohydrate drinks and fasting, since ERAS makes no general recommendation on carbohydrate drinks for people with diabetes [10].
• Do not self-prescribe high doses of vitamins or minerals to "build up" before surgery. Testing first lets your team correct a real deficiency safely.

Frequently Asked Questions

Can I take supplements to fix nutrient deficiencies before surgery?

Sometimes, but only with your team's agreement. A blood test can show whether you have a deficiency such as low iron, and your team can then choose the right product, dose and timing. Other supplements may need to be stopped before surgery.

Which supplements should I stop before surgery?

Supplements often flagged include fish oil, vitamin E, ginkgo, garlic, ginseng, St. John's wort, kava and valerian. Anesthesiologists may recommend stopping supplements at least two weeks before surgery. Ask your own team for a list that fits your procedure.

What is carbohydrate loading before surgery?

It is a specially formulated carbohydrate drink taken the evening before and a few hours before surgery in some enhanced recovery pathways. It is not suitable for everyone, so only use it if your surgical team prescribes it and follow their timing exactly.

How soon before surgery should I improve my diet?

As early as you can. For people at risk of malnutrition, ERAS recommends nutrition treatment for at least 7 to 10 days before surgery, and screening needs to happen before that.

Should I eat more protein before surgery?

Make sure you eat enough. Experts consider protein delivery more important than total calories around surgery. Include a protein food at each meal and ask your team about an oral nutrition supplement if your appetite is poor.

Sources

1. Office of Dietary Supplements. Omega-3 Fatty Acids: Fact Sheet for Health Professionals. National Institutes of Health.
2. Office of Dietary Supplements. Vitamin E: Fact Sheet for Health Professionals. National Institutes of Health.
3. National Center for Complementary and Integrative Health. Using Dietary Supplements Wisely. National Institutes of Health.
4. National Center for Complementary and Integrative Health. Garlic. National Institutes of Health.
5. National Center for Complementary and Integrative Health. Ginkgo. National Institutes of Health.
6. National Center for Complementary and Integrative Health. Asian Ginseng. National Institutes of Health.
7. National Center for Complementary and Integrative Health. St. John's Wort. National Institutes of Health.
8. National Center for Complementary and Integrative Health. Kava. National Institutes of Health.
9. American Society of Anesthesiologists. Herbal and Dietary Supplements and Anesthesia. 2020.
10. Gustafsson UO, Scott MJ, Hubner M, et al. Guidelines for perioperative care in elective colorectal surgery: Enhanced Recovery After Surgery (ERAS) Society recommendations: 2018. World Journal of Surgery. 2019.
11. Weimann A, Braga M, Carli F, et al. ESPEN practical guideline: clinical nutrition in surgery. Clinical Nutrition. 2021.
12. Wischmeyer PE, Carli F, Evans DC, et al. American Society for Enhanced Recovery and Perioperative Quality Initiative joint consensus statement on nutrition screening and therapy within a surgical enhanced recovery pathway. Anesthesia & Analgesia. 2018.

Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.

Written and reviewed by Michael Gonzales, Founder, OPA Nutrition · Last reviewed: October 17, 2026 · How OPA researches and writes