The Big Gastric Bypass Diet Guide

Table of Contents

Gastric bypass surgery is often a lifesaving procedure. You can expect to lose weight faster than you ever have before, reduce many co-morbidities (some immediately after surgery!), and likely look and feel better than you have in the past. However, to be successful (long-term), you will likely  need to change many behaviors, including the food choices you make.

You don’t have to make these changes alone! Find a surgery center that has the support you need to help you make these changes permanent. Look for a support group, whether it’s in person, or on-line, connecting with other people who are going through a similar experience to you has many benefits. Studies have shown that people who attend support group after surgery tend to have greater weight loss outcomes than those who don’t. Also, if you are struggling with any aspect of life after surgery, you can get the support you need from peers and professionals alike.

Knowing what you can and can’t eat is the first step towards healthy food choices after surgery. Your diet for the first few  weeks after gastric bypass surgery is important for two reasons.

  1. Your safety. Eating certain  foods could put undue pressure on your healing stomach.
  2. Establishing a new way of eating, with a focus on protein. Luckily, your hunger levels change immediately after surgery and most people do not feel the sensation of hunger the way they did prior to surgery – this makes it easier to follow the diet plan after surgery compared to any diet you’ve tried before.

Pre-Op Liquid Diet

Most surgery centers recommend following a pre-op liquid diet in order to reduce the amount of fat around the liver and spleen. Typically, a preoperative liquid diet must be followed 7-14 days before gastric bypass surgery.  Your liver sits on top of your stomach, which is where the surgeon will be performing your surgery. A large liver can make it more difficult for your surgeon to visualize your stomach during the procedure. If the liver is too large, it then it can become unsafe to perform your gastric bypass surgery. Sometimes, surgery may then be canceled and rescheduled to a later date.

I can’t stress enough how important it is to follow the pre-op diet. You’ve likely waited 6 months to a year to get approved and on the operating table. Follow the  pre-op diet as recommended by your bariatric doctors office.

The 1-2 week pre-op diet will likely include the following elements, but be sure to follow the instructions from your doctor’s office:

  • Protein shakes or meal replacement shakes will make up the majority of your diet during this time .
  • Only sugar-free beverages are allowed (sugar substitutes are okay).
  • No caffeinated or carbonated beverages are permitted.
  • Soup broth with no solid pieces of food may be consumed.
  • V8 and vegetable juice are acceptable.
  • Extremely thin cream of wheat or cream of rice may also be eaten.
  • One or two daily servings of lean meat and/or vegetables might be okay, but only if they are approved by your surgeon or registered dietitian.

Separating your liquids and solids applies post-operatively (after surgery) it’s a good habit to start pre-operatively.

A daily meal plan for your pre-op liquid diet may look like this:

High Protein Meal Replacements

During the pre-op phase (prior to surgery) your body will go into ketosis. This allows your body to use your fat stores as an energy source. The result is the fat in your liver shrinks considerably in a short amount of time. As seen above, your diet is high in protein and low in carbohydrates. Below are some suggested high protein meal replacements:

  • Bariatric Advantage
  • Syntrax Nectar
  • EAS Myoplex Light/Carb Control
  • Isopure
  • Unjury
  • Chike
  • GNC Total Lean Shake 25

Notes Pre-Op

Talk to your doctor about stopping certain medications prior to surgery. The following medications are typically stopped 1 week prior to surgery and may require tapering down the dose.

  • Coumadin
  • Steroids
  • Other anti-coagulation medications
  • Aspirin, Motrin, Advil, Celebrex, and any other NSAIDs
  • Replacement hormones
  • Birth control

If you have sleep apnea and use a CPAP machine, plan on bringing it to the hospital. Purchase vitamins and supplements in advance of surgery. Find a  protein shake that you like the taste of, but keep in mind taste preferences will likely change after surgery – so you may want to have a few different brands on hand at home.

If you smoke you should stop prior to surgery. Smoker’s have an increased risk of blood clots and complications during and after surgery. Make a plan and implement it a few weeks prior to surgery.

Post-Op Dietary Guidelines

Once gastric bypass surgery is complete, a strict post-op diet plan needs to be followed. There is now a staple line in your stomach that must be allowed to heal. Certain foods can disrupt the healing process, put undue stress on the staple line, and lead to a leak. The following information is an example of post-op dietary guidelines. However, each surgery center varies slightly on what they tell their patients to consume. Always follow the advice of your surgeons office.

The diet for a post-op gastric bypass patient typically consists of four stages:

Week 1 – Clear Liquids

For 1 to 7 days after gastric bypass surgery, only clear liquids are to be consumed. Remember the stomach pouch is brand new at this time, and it is extremely swollen. You will likely need to sip constantly throughout the day in order to reach your daily fluid goals. A good goal is to consume 6-8 ounces of fluid per waking hour.  Your  dietitian will decide how long this phase will last and suggest dietary guidelines to follow.

Clear liquids recommended by the dietitian will probably include the following items:

  • water
  • caffeine free herbal tea fat-free broth
  • sugar-free Jell-O (many programs recommend avoiding red colored Jell-O; this is just a precaution in case you spit up from drinking too fast and saw a bright red color, you or your doctor may think it is blood and rush you for tests)

During this phase, it’s important to stay hydrated. Some surgeons may want you to start protein shakes a few days after surgery. Follow your surgeon’s guidelines.

Week Two and Three – Pureed Foods and Protein Shakes

After 1 to 7 days of drinking clear liquids, you will be given permission to consume liquefied sources of protein. This stage of the post-op diet will usually last for one week (occasionally 2).

Because of the patient’s smaller stomach size, the individual should have several smaller meals throughout the day. Your daily intake should be about 60-70 grams of protein (protein shakes, egg whites, pureed meat/fish) and approximately 64 ounces (about 8 glasses) of clear liquids (as defined in stage one) not counting the fluid in the pureed foods.

Caffeinated and carbonated beverages should not  be consumed. Refined sugars and simple carbohydrates  should be avoided as well.

Below is a list of the pureed protein sources that are typically allowed by your dietitian or surgeon:

  • Protein shakes
  • Non fat milk
  • Egg whites
  • Non-fat soft cheese
  • Non-fat cottage cheese
  • High protein, low sugar yogurt

Clear liquids should be sipped very slowly, and straws should not be used because they might bring unwanted air into the stomach, which could lead to discomfort.

It is necessary to take one or two multivitamins (containing iron) every day in order to prevent nutrient deficiencies. The multivitamins should be in chewable or liquid form during this time.

It is also important to supplement your diet with calcium citrate; the recommended amount will usually be two or three doses with each dose ranging from 400 mg to 600 mg. Calcium citrate supplementation should be separated from the multivitamin dosages by at least two hours. This is because iron and calcium can interfere with each others absorption, leading you to not get the amount that your body needs.

A stage two meal plan might look like this:

Week 4 and 5 – Soft Foods

This stage of the diet will allow for a very gradual reintroduction of soft foods into your diet. This stage usually lasts about 1 or 2 weeks.

If a food can be easily mashed with a fork,  or a spoon, then it is probably a candidate for stage three of the post-op gastric bypass diet. This portion of the diet will likely include soft meats and cooked vegetables.

The nutrient goals will remain the same as in stage two. 60+ grams of protein and 64+ ounces of fluid is recommended daily. The serving size of protein in stage three should be about 1 to 2 ounces (an ounce is about the size of your thumb) and you’ll likely have 3 to 6 small meals.

Stage three, like stage two, focuses on high-quality lean protein sources. While stage 3 continues to focus on high-quality lean protein sources, up to three servings of soft vegetables may also be allowed; a tiny portion of fat may also be permitted (this small portion of fat will probably be from a single serving of ripe avocado).

Recommendations for the protein sources in this stage of the diet will probably include several of the following items:

Meat, Dairy, and Eggs

  • lean chicken
  • lean turkey
  • fish
  • egg whites
  • non-fat cottage cheese
  • non-fat cheese
  • tofu


  • potatoes
  • carrots
  • green beans
  • tomatoes
  • squash
  • cucumbers
  • bananas
  • avocados

You will still need to take your multivitamin and two to three 400-600 mg doses of calcium citrate (with each of these doses to be taken at least two hours apart from each other, and away from your multivitamin).

Your dietitian may recommend you take 3,000 IU of Vitamin D3 total per day, which will likely be found in your bariatric specific multivitamin and calcium.  It is important to make sure you are taking at least 12 mg of thiamin and at least 350 mcg of vitamin B12, luckily these doses are provided in most bariatric specific multivitamins.

This is what a typical stage three meal plan might look like:

* finely diced and moist / ** boiled or steamed until very soft / *** must be ripe enough to be soft / **** mashed

Week 6 – Solid Foods

Solid food is back! You’ve made it this far and it’s time to start eating real food. At this stage it is so important to practice mindful eating. Make sure that every meal you eat you are sitting down and paying attention to how your body feels. Take small (dime sized) bites, put your fork down between each bite, chew until applesauce consistency before you swallow, set a timer and do not take longer than 20 minutes to eat your meal.

A diet consisting of protein, vegetables, a limited amount of grains, and very little, if any, refined sugars should be followed for the rest of your life.

Tips for starting solid foods:

  • Introduce one new food at a time; ideally not more than one new food a day so you can gauge your body’s reaction.
  • Eat slowly. Chew your food well, 15 seconds each bite. Use the timer on the Baritastic app.
  • Separate your food and water by at least 30 minutes.
  • Continue to drink at least 64 ounces of water a day.
  • Eat your protein first, vegetables second and carbohydrates third (ideally healthy grains and/or fruits, not processed foods).

Dumping syndrome occurs when sweet and/or fatty foods have been consumed too quickly or in too large a quantity. The stomach dumps the food into the small intestine before it’s properly broken down. Dumping syndrome usually causes nauseousness, cramping, diarrhea, sweating, vomiting, or an increase in heart rate; these symptoms usually wear off after one or two hours. But the experience of ‘dumping’ is very unpleasant and you’ll want to avoid it.

To reduce the risk of dumping:

  1. Avoid high sugar/refined carbohydrate foods.
  2. Eat very slowly.
  3. Chew your food well.

Certain foods are very difficult to digest and should be approached with caution:

  • beef
  • pork
  • shellfish
  • grapes
  • nuts
  • whole grains
  • corn
  • beans
  • salad / lettuce
  • asparagus
  • pineapple

Basically, the same guidelines found in stage three will be carried over into this fourth and final stage of your  post-op dietary plan. The protein intake, vitamin supplementation, and liquid requirements remain the same.

More fruits and vegetables (both cooked and raw) may now be carefully added to your diet. Small amounts of fat and very small amounts of sugar may now be added with caution. Carbonated and caffeinated beverages may now be consumed in moderation.

The total caloric intake per day will usually range from 800 to 1,200 and up to 1,500 18 months after surgery.

A stage four meal plan could look like this:

Physical Activity And Exercise

Your program will likely encourage tracking your steps every day, this is a great habit to start even before surgery. A simple goal can be to take one more step each day than you did the day before. Your program may give you a daily step goal immediately after surgery, as it’s important to walk often to protect against the possibility of getting a blood clot. . Walking, running, biking, weight lifting, aerobics, canoeing, badminton, hiking, and dancing in your bedroom like a crazy person can all be added to your weekly routine. Ensure that you are getting at least 30 minutes of exercise 5 to 7 days a week. It doesn’t matter how you do it, just do it.

Note: Do not lift more than 10 pounds for at least 6 weeks after surgery. This can put undue pressure on your internal stitches and result in a hernia.

Choosing Gastric Bypass Appropriate Foods

In general, you’ll want to choose foods that are high to moderate in protein, low in carbohydrates and moderate in good fats.

Foods with good (healthy) fats include:

  • avocados
  • salmon
  • nuts
  • sardines
  • nut butters
  • coconut oil

General guidelines include:

  • Choose lean meats.
  • Canned tuna and salmon.
  • Avoid greasy and spicy foods.
  • Avoid whole milk.
  • Eat nutrient dense foods (whole fruits, vegetables, meats, eggs).
  • Plan your meals.
  • Involve your family in healthy eating decisions.
  • Shop for healthy foods.
  • Limit or eliminate desserts.
  • Eliminate fast food.
  • Eat out only on occasion.
  • Take quality nutritional supplements/vitamins.
  • Separate your water and food by at least 30 minutes.
  • Introduce new foods slowly.

Recommended Articles

To calculate your expected weight loss after gastric bypass surgery, use our calculator.


Gastric bypass is one of the safest and most effective forms of weight loss surgery. For this reason, it is often referred to as the “gold standard.”

You will lose weight with gastric bypass surgery –  studies indicate that you will lose more than 50% of your excess weight, and keep it off long-term. You may feel overwhelmed at the changes you need to implement after surgery, and that is perfectly normal. The surgery will give you a jump start on changing your habits, it is important to continue those habits lifelong. Tracking your daily food intake, physical activity levels, staying hydrated, taking your supplements, and finding a support system are ways to ensure success after surgery. Find an app that you like using to help you track your new habits!

For more information about gastric bypass surgery, check out our Expert’s Guide To Gastric Bypass.

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