Undergoing Gastric Bypass Surgery requires patients to undergo a 2-day to 8-week pre-op diet depending on the patients BMI.

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.

What is the Purpose of the Pre-Op Diet?

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.

Pre-Op Diet Tips

  • 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 RNY Gastric Bypass 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.

Behavior/Lifestyle Changes

  • Discontinue ALL carbonated beverages.

  • Discontinue ALL beverages with caffeine.

  • Cut food into SMALL pieces and practice chewing foods thoroughly.

  • 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.

  • Begin a routine exercise program (consult with your physician first).

  • LIFELONG HABIT: Do NOT drink with meals.

Overview of the Gastric Bypass Pre-Op Diet

For most people undergoing gastric bypass surgery, the duration of the pre-op diet depends on your Body Mass Index. Check the BMI requirements to see how long you will need to follow the pre-operative diet guidelines.

This diet is general and can be modified to accommodate specific needs for each person. So use this as a general guideline. Especially for people who have diabetes; you want to make sure you monitor your blood sugar levels and change your medications accordingly.

  • 2 – 3 protein shakes per day – You may purchase these online, at nutrition stores, or most grocery stores.

  • You can eat as many raw or cooked vegetables as you want (All vegetables witht the exception of peas and corn)

  • 2 servings of 4 oz. lean protein (ex. chicken, turkey, fish, lean ground beef, eggs, tofu)

  • 1 – 2 servings of healthy fats (ex. dressings, some nuts, avocado)

  • You can add ½ cup of frozen berries or ½ banana to your protein shake

  • You can make your shake with unsweetened vanilla almond milk or coconut milk (no regular milk- too much sugar)

  • Absolutely NO bread, rice, pasta, potatoes, sweet potatoes, yams, cereals, oatmeal, popcorn, refined grains, corn, peas, or sauces with sugar.

Sample Meal Plan for Pre-Op Diet

An ideal meal plan might look like a protein shake for breakfast, your food meal for lunch, protein shake for dinner, and then if needed another protein shake in the evening. Now if you prefer to have 2 shakes and 2 meals consisting of 4 oz. of pure protein like chicken, turkey or fish, and as many vegetables as you want and a healthy fat that is fine as well.

  • Breakfast: 1 protein shake

  • Mid-morning snack: 1 protein shake

  • Lunch: Raw or cooked vegetables (you can 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.

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

Pre-Op Protein Guidelines

First, let’s look at your protein. You want to make sure you have a protein powder that has at least 20 grams of protein per serving and has less than half that of sugar.

So what does that mean? If you have a protein shake that has 20 grams of protein, then it needs to have less than 10 grams of sugar.

Looking at premade drinks for example this one has 25 g. of protein and 5 g. of sugar so this is fine. Now this protein drink has 10 grams of protein and 18 grams of sugar; this is for sure a NO. Never get a protein drink that has more sugar than protein… Ever. The most important thing to realize is you have to read the labels.

Protein Shake Approved Ingredients

I prefer you get a protein powder and make your own. If you are making your protein shake; here are some things you can put in it.

  • Protein Isolates

  • 8 ounces Unsweetened Vanilla, Almond or Coconut Milk

  • 1 TBSP of a Healthy Fat Like Coconut Oil

  • Barlean’s Essential Fatty Acids

  • ½ Avocado

  • Almond Butter

  • Chia Seeds

Chia Seeds: I cannot say enough about chia seeds. These are a Superfood, loaded with nutrients. Chia Seeds are high in fiber and an excellent source of protein, calcium, magnesium, and much more. They are high in tryptophan the amino acid needed to make them feel good hormone serotonin and they expand 9 times their amount so they make you feel satisfied, longer.

14 Days Prior to Gastric Bypass Surgery

  • Discontinue birth control and Estrogen replacement (HRT) medications.

  • Discontinue all vitamins supplements

  • Do not take any herbal medications/remedies

7 Days Prior to Gastric Bypass Surgery

  • 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 Vitamin E

  • For a headache or minor pains, you may use Tylenol.

  • Do not take any herbal medications/remedies.

For 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 Gastric Bypass Surgery – Clear Liquid Diet

  • Clear Liquids Only: 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 Gastric Bypass 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.

We hope that this information on the RNY gastric bypass surgery pre-op diet and nutrition guidelines helps you transition into a healthier you. If you have any further questions, you are welcome to contact us at any time.

Guide to Gastric Bypass Surgery: