Carb Loading Drink Before Surgery: How to Choose One and When to Drink It

Written by the Thrive Protocol editorial team. Medically reviewed by Dr. Patrick Denard, orthopaedic surgeon, on October 19, 2026

This page is about choosing and timing the drink itself. For the research on why carb loading exists, read our post on carb loading before surgery. For dinner the night before, see what to eat the night before surgery. For the whole pre-op month, start with pre-surgery nutrition.

Disclosure: Thrive Protocol makes OptiCharge, a carbohydrate and electrolyte drink included in our Surgical Protocol Kit. We compare it with other options below using each maker's own published information.

What the guidelines actually say

• American Society of Anesthesiologists (ASA), 2023: "We recommend healthy adults drink carbohydrate-containing clear liquids until 2 h before elective procedures." The carbohydrate can be simple or complex, and up to 400 mL is considered an appropriate volume (1).
• ESPEN, the European surgical nutrition society: to reduce discomfort, including anxiety, a carbohydrate drink should be given the night before and 2 hours before surgery, instead of fasting overnight (2, 3).
• ERAS Society, hip and knee replacement: carb loading may improve well-being and metabolism, but it has not been shown to speed discharge or reduce complications, so it is not recommended as an essential routine step (4).
• The evidence in one line: a Cochrane review of 27 trials linked carb drinks with a hospital stay about 0.3 days shorter than fasting or placebo, on very low-quality evidence, with no change in complications and no aspiration reported (5).

So the drink is mainly about arriving less hungry, thirsty and anxious. In the best-known trial, patients who drank a 12.5% carbohydrate drink were less hungry and less anxious before surgery than patients who fasted or drank flavored water, with no increase in stomach fluid (6).

How to choose a pre-op carbohydrate drink: a 5-point checklist

1. Enough carbohydrate. The Cochrane review only counted treatments with at least 45 g of carbohydrate within 4 hours of surgery (5). The classic trial regimen was 800 mL the night before and 400 mL in the morning of a 12.5% drink (6), which works out to 100 g and 50 g.
2. Clear and simple. No milk, cream, pulp, fat or fiber. A milk-based protein shake is not a clear liquid.
3. Protein is not needed. The ASA found insufficient evidence to recommend protein-containing clear liquids over other clear liquids (1).
4. A volume you can finish. About 400 mL (13.5 oz) is the ASA's appropriate volume for the pre-op window (1).
5. Approved by your team, in writing. Many hospitals supply their own drink or name one. If they do, use theirs.

Carb loading drinks compared

Facts below come from each maker's own page or label, or the named retail listing, checked on 18 October 2026. Prices change, so treat them as a snapshot.

Read the table as a fit check, not a ranking. The ready-to-drink bottles suit people who want the exact regimen their hospital uses. OptiCharge suits people who want the evening drink bundled with a week of daily protein before surgery. Whatever you buy, the drink your anesthesia team names comes first.

Timing: a worked example

Say your surgery is scheduled for 10:00 am and your written instructions allow clear liquids until 2 hours before. Here is how a typical plan lines up. Your hospital's times win if they differ.

Two common slips: counting 2 hours from your arrival time instead of the start time your team gave you, and sipping slowly past the cut-off. When in doubt, call the pre-op nurse the day before and confirm the time in plain words.

Who should check with their care team first

The ASA guidance applies to healthy adults having elective procedures. It lists conditions that can raise the chance of stomach contents reaching the lungs, so your anesthesiologist adjusts the plan (1):

• Insulin-dependent diabetes (most people with diabetes can carb load; see below)
• Gastroparesis, or significant uncontrolled reflux or hiatal hernia
• Previous stomach surgery, such as gastric bypass
• Regular opioid use
• Pregnancy or obesity
• Bowel obstruction or emergency surgery

Diabetes: diabetes is not a reason to skip carb loading. For most people with diabetes it is safe, but if you are insulin dependent, check with your physician first. The ASA notes carbohydrate drinks can raise blood sugar, especially if you reduce your diabetes medicine before surgery, and home glucose readings may help guide the plan (1). Thrive likewise asks people with type 1 diabetes to get their physician's OK before using OptiCharge.

GLP-1 medicines such as semaglutide or tirzepatide slow stomach emptying. Multi-society guidance says decisions should be shared between you, your surgeon, anesthesia team and prescriber, and some patients may be asked to follow a liquid diet for at least 24 hours before surgery (7). Raise this early.

Common questions about the drink itself

Can I use Gatorade or juice? Some hospitals allow a sports drink or pulp-free juice, and the ASA lists juice without pulp as a clear liquid (1). The catch is the dose: a 20 oz Gatorade Thirst Quencher has 36 g of carbohydrate, less than the 50 g in purpose-made pre-op drinks. Color can matter too. One hospital clear-liquid sheet for people with diabetes allows Gatorade but says to avoid red or purple drinks (8). Only swap if your team says so.

Can I add protein powder to it? No. Protein is not needed, and powders often contain milk, which is not a clear liquid (1). Save your protein shake for the days before and after surgery.

What if I forget the evening drink? Do not double up in the morning. Follow your written instructions and mention it at check-in.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Want the full checklist for the weeks before surgery? Get the free Surgery Recovery Guide.

When to call your care team

• Your written fasting instructions conflict with what you were told by phone.
• You are vomiting or cannot keep fluids down in the days before surgery.
• Your blood sugar readings are outside your target range the night before or morning of surgery.
• You started, stopped or changed a GLP-1 medicine, insulin or another diabetes medicine.

Frequently asked questions

What is a carb loading drink before surgery?

A clear drink with a measured dose of carbohydrate, usually maltodextrin or sugar in water, taken the evening before and sometimes up to 2 hours before surgery. It replaces long overnight fasting for people their anesthesia team approves.

How many grams of carbs should a pre-op drink have?

The best-known trial used about 100 g the evening before and about 50 g in the morning dose. The Cochrane review required at least 45 g within 4 hours of surgery to count as carbohydrate treatment.

What can I drink before surgery?

For healthy adults, clear liquids such as water, pulp-free juice, black coffee or black tea are usually allowed until 2 hours before a planned procedure. Your hospital may set an earlier time, and its instructions come first.

Is Ensure Pre-Surgery the same as Ensure Surgery?

No. Ensure Pre-Surgery is a clear carbohydrate drink with 0 g protein and 0 g fat. Abbott's Ensure Surgery Immunonutrition Shake is a different product with 18 g protein and 9 g fat per 8 fl oz, so it is not a clear liquid and is not a pre-op carb drink.

Can people with diabetes use a carb loading drink?

In most cases, yes. Diabetes is not a contraindication, but if you are insulin dependent, check with your physician first, because carbohydrate drinks can raise blood sugar. Thrive asks people with type 1 diabetes to get their physician's OK before using OptiCharge.

Related reading

• Carb loading before surgery: the research
• What to eat the night before surgery
• Pre-surgery nutrition
• Glucose control after surgery

References

1. Joshi GP, et al. 2023 American Society of Anesthesiologists practice guidelines for preoperative fasting: carbohydrate-containing clear liquids with or without protein, chewing gum, and pediatric fasting duration. Anesthesiology. 2023;138(2):132-151. PubMed 36629465
2. Weimann A, et al. ESPEN guideline: Clinical nutrition in surgery. Clin Nutr. 2017;36(3):623-650. PubMed 28385477
3. Weimann A, et al. ESPEN practical guideline: Clinical nutrition in surgery. Clin Nutr. 2021;40(7):4745-4761. PubMed 34242915
4. Wainwright TW, et al. Consensus statement for perioperative care in total hip replacement and total knee replacement surgery: ERAS Society recommendations. Acta Orthop. 2020;91(1):3-19. PubMed 31663402
5. Smith MD, et al. Preoperative carbohydrate treatment for enhancing recovery after elective surgery. Cochrane Database Syst Rev. 2014;(8):CD009161. PubMed 25121931
6. Hausel J, et al. A carbohydrate-rich drink reduces preoperative discomfort in elective surgery patients. Anesth Analg. 2001;93(5):1344-1350. PubMed 11682427
7. Kindel TL, et al. Multi-society clinical practice guidance for the safe use of glucagon-like peptide-1 receptor agonists in the perioperative period. Surg Endosc. 2025;39(1):180-183. PubMed 39370500
8. UMass Chan Medical School Diabetes Center of Excellence. Preparing for surgery or procedures: clear liquid diet for people living with diabetes. umassmed.edu (PDF)

This guide is for education and does not replace your anesthesia team's instructions. Product details checked against maker websites, retailer listings and labels on 18 October 2026. Prices change; check before you buy.