Gastric Bypass Surgery Pre-Op Diet

Undergoing Gastric Bypass Surgery requires patients to undergo a 2-day to 8-week pre-op diet depending on the patients BMI. This gastric bypass pre-op diet is specially designed to shrink fatty liver, a condition that many obese patients have.

By following a liver shrinking diet before gastric bypass surgery, bariatric surgeons have more control and will be able to perform your procedure safely. Through shrinking the fatty liver with the pre-op liquid diet, surgeons are better able to visualize the stomach and thus, perform the gastric bypass surgery effectively.

The goal of the pre-op gastric bypass diet plan is to consume 1000 to 1200 calories per day with liquids only. Because many patients consume 3,000 to 5,000 calories per day, many patients will have unpleasant feelings consuming this diet, namely irritability and headaches. Most patients will adjust to the new diet in a few days, and their unpleasant feelings will subside. It’s important to undergo this procedure

Important Guidelines Before Gastric Bypass Surgery

  • It’s important to consume enough water while on the liquid-only diet.
  • Do not take any herbal medications for seven days before surgery.
  • Diabetics need to monitor your blood sugars and contact your doctor if necessary.
  • Do not take any aspirin, Advil, Nuprin, Aleve or any other non-steroidal anti-inflammatory medication for seven days before surgery. These drugs cause profuse bleeding after surgery. This includes baby aspirin and most arthritis medications. If you are not sure, please check with our Doctors. For a headache or minor pains, you may use Tylenol. You may restart these medications the next day after surgery.
  • You may take needed medications (such as heart or blood pressure medications) with sips of water the morning of surgery as directed by our Doctors.
  • (This Diet is the Same as the Pre-Op Diet for Gastric Sleeve Surgery)

Prior to Surgery

  • Do not smoke 30 days prior to surgery
  • Start taking a probiotic 6 weeks prior to surgery or as soon as possible. You want one that has a minimum of 50 billion units and the more strains the more effective.

Gastric Bypass Pre-Op Diet Plan

Protein Powder/Drinks

You may purchase these in any health food store or many grocery stores. Please be sure it contains at least 20 grams of protein per serving.  Sugar should be half the grams or less than protein- if you have 20 grams of protein, it should have less than 10 grams of sugar

General Overview

  1. 2 – 3 protein shakes per day
  2. You can eat as many raw or cooked vegetables as you want (All vegetables are included except peas & corn)
  3. 2 servings of 4 oz. of a lean protein (chicken, turkey, fish, lean ground beef, eggs, tofu, beans of any kind except baked or BBQ beans. (you can have more than 4 oz.; this is the minimum per serving)
  4. 1 – 2 servings of a healthy fat (salad dressing, olive oil, nuts, avocado, olives)
  5.  You can add ½ cup of frozen berries or ½ banana to your protein shake
  6. You can make your shake with unsweetened vanilla almond milk or coconut milk (no regular milk- too much sugar)
  7. Absolutely NO bread, rice, pasta, potatoes, sweet potatoes, yams, cereals, oatmeal, popcorn, refined grains, corn, peas, sauces with sugar

*Weight loss soup recipe

Sample Meal Plan Before Gastric Bypass Surgery

Breakfast: 1 protein shake

Mid-morning snack: 1 protein shake

Lunch: Raw or cooked vegetables (ok to add one TBSP olive oil or butter spray to veggies) and 4 oz.  lean meat. Example: Tilapia with baked broccoli seasoned w/ olive oil and slivered almonds

Dinner: Salad with Protein (chicken, fish, egg, etc.), a small amount of no or low sugar dressing (preferably olive oil & vinegar or Lemon).

Evening Snack: 1 protein shake (if needed).

You may also add 1 TBSP chia seeds to your shakes or take psyllium husk to help you stay satisfied throughout the day.

* Patients with higher or lower BMI and/or other medical conditions may be prescribed other dietary prerequisites in addition to the above pre-op diet.

The purpose of this diet is to help shrink your liver prior to surgery by depleting stored glycogen.

* You may at this time drink other drinks as long as they have NO SUGAR

Behavior/Lifestyle Changes

  • Discontinue ALL carbonated beverages.
  • Discontinue ALL beverages with caffeine.
  • Begin a routine exercise program (consult with your physician first).
  • Cut food into SMALL pieces and practice chewing foods VERY well.
  • Discontinue ALL over the counter Herbal supplements.
  • VERY IMPORTANT: Stop drinking 30 minutes prior to eating and DO NOT drink until 30 minutes after a meal.


14 Days Prior to Gastric Bypass Surgery

  • Discontinue all Vitamins
  • Do not take any herbal medications/remedies.

7 Days Prior to Gastric Bypass Surgery

  • Some medications may need to be discontinued before surgery depending on the instructions of your physician.
  • Specific medications to discontinue: Coumadin, Plavix, Aspirin, Ibuprofen, Motrin, Advil, Nuprin, Aleve or any other non-steroidal anti-inflammatory medication. **Remember this also includes baby aspirin and most arthritis medications. As these can all cause stomach irritation and possibly more bleeding post-op gastric bypass surgery.
  • Discontinue birth control and supplemental hormones
  • Discontinue Vitamin E
  • For a headache or minor pains, you may use Tylenol.
  • Do not take any herbal medications/remedies.
  • Diabetes Patients:
    • May continue to take medication up to the day of surgery. Be mindful, medications and amounts may change due to diet and weight loss change prior to surgery.
    • MUST consult with their doctors about medication use.
    • MUST check sugar levels at home. If sugar is above 150 call your primary care physician immediately.

2 Days Prior to Surgery – Begin Clear Liquid Diet

  • Consume only clear liquids:
    • Apple or other clear juice without pulp or carbonation
    • Clear broths: Chicken, Vegetable, or Beef
  • Water or Flavored Water
  • Need to have 2 Greek yogurts per day (maybe flavored but no pieces of fruit) – this helps with post healing and providing healthy bacteria in your gut. Plain Greek yogurt is your best option or something similar

8 Hours Prior to Surgery

  • Absolutely nothing to drink after the midnight preceding surgery or 8 hours prior to your surgery.
  • Absolutely NO medications unless directed by the doctor. (If you have been pre-approved to take any medications by your doctor leading up to surgery, you may take small sips of water for swallowing.)
  • Please bring ALL your prescribed medications (whether you are currently taking them or not) in properly labeled pharmaceutical bottles for documentation during Pre-Op testing. Do NOT take any medications after surgery until you have consulted with the doctor(s) and gotten approval.

Guide to Gastric Bypass Surgery: