Bariatric Surgery Pre-op Diet for Vegans. cup of water with lemon wedge. bowl of food with chickpeas, vegetables, and avocado. vegan bariatric dietitian logo

Bariatric Surgery Pre op Diet for Vegans

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Following a special bariatric surgery pre-op diet and working with a dietitian are very common before bariatric surgery. But what if you’re vegan? How can you stay vegan and meet your pre-surgery nutrition goals?

Yes you can! And I am going to tell you how in this article.

Why Do You Need a Bariatric Surgery Pre-op Diet?

A bariatric surgery pre-op diet is recommended for several reasons before bariatric surgery. 

The first reason is that weight loss and/or visits with a dietitian may be required by your health insurance company for them to pay for your surgery. We have known for years that there is limited evidence as to the benefit of mandated weight loss prior to bariatric surgery. Unfortunately this doesn’t stop all insurance companies from requiring it prior to bariatric surgery.

The bariatric surgery pre-op diet that your dietitian helps you to follow will help with weight loss prior to surgery. This is especially important for you if your insurance company requires this.

The amount of weight that you may need to lose before bariatric surgery will vary. This depends on your particular bariatric program, your health insurance company, and your individual needs (for example, there may be weight limits on some of the equipment used for the surgery).  

The second reason that you need a bariatric surgery pre-op diet is liver reduction. Almost all bariatric programs require a pre-op liver reduction diet. A liver reduction diet is a temporary low calorie and low carbohydrate diet that helps to reduce liver glycogen (carbohydrate storage). This reduction in glycogen helps to reduce the size of the liver and therefore makes the surgery easier for the doctor to perform safely.

What is a Bariatric Surgery Pre-op Diet?

Typically there are two parts to a bariatric surgery pre-op diet. There is the liver reduction part right before surgery and usually a period of time before the liver reduction diet that you are working with the dietitian or your bariatric program. 

Initial Preoperative Visits

The initial visits that you have with your bariatric dietitian will typically involve a thorough nutrition assessment so that your dietitian can find out about your current nutrition habits. Once you’ve shared this information, your dietitian will help you work on nutrition interventions to align your nutrition habits with habits that will help you be successful after bariatric surgery. 

These initial visits typically last from 2-6 months, depending on your bariatric surgery center and health insurance plan. 

During this time you should be working on nutrition habits that will be helpful to you after bariatric surgery. 

Nutrition Habits to Establish Before Bariatric Surgery

Foods to Eat
  • Make sure you’re eating balanced meals. Include a variety of foods in your meals and snacks, such as legumes, whole grains, fruits, vegetables, and healthy fats. It is NOT necessary to ‘cut out all carbs.’ This behavior typically leads to cravings and low energy. Foods that are rich in carbohydrates are good for you.
carbs: bread, bananas, fruit, legumes, pasta, corn, tomatoes, potatoes, rice, quinoa
  • Decrease your fast food consumption.
  • Try a variety of protein shakes. You are going to need these to meet your nutrition goals after bariatric surgery so you should find some that you like.
  • Work towards adequate hydration every day. Most people need 48-64 ounces of fluid each day. These should be mostly low or no-calorie fluids.
  • Wean down your consumption and then fully avoid foods/ingredients that need to be limited/avoided after bariatric surgery:
    • If you drink alcohol, start decreasing and then eliminate it. Alcohol should be avoided in the early postoperative time after bariatric surgery. Limited amounts may be allowed when you are further out from surgery. Learn more about alcohol in my ‘Alcohol After Bariatric Surgery’ article linked here.
    • If you drink carbonated beverages, start decreasing and then eliminate them. Carbonated beverages can make you feel uncomfortably full after bariatric surgery
    • If you use caffeine, start decreasing it. During the immediate postoperative period you should avoid caffeine. Once you are fully healed from the surgery and are able stay hydrated it is typically allowable to include some caffeine in the diet. 
How to Eat
  • Get used to taking vitamin and mineral supplements. To practice this habit you will usually be encouraged to start taking a daily multivitamin with minerals supplement.
  • Developing an eating schedule. This is going to look different for each person. Usually 3 meals and 1-2 snacks are recommended.
  • Practice avoiding drinking during meals. This is such a difficult and important habit that you need to follow after bariatric surgery.
  • Work on practicing mindful eating habits. When you’re eating, don’t do other things such as watch TV, read, or scroll on your mobile phone. Get in the habit of eating when you’re hungry and stopping when you’re full
  • Track your eating and physical activity. This helps you to better stick to your goals and also provides information on how you’re doing to your dietitian. Your dietitian has a much more difficult time helping you if they only have a vague idea of what you’re actually doing.
  • Measure your food to make sure you’re eating appropriate portions. This will be different for each person. Your program’s dietitian can help you determine the right portions for you.
photo of a plate illustrating bariatric pre-op meal with 1/2 plate veggies: lettuce, carrots, tomatoes providing low calories and fiber, 1/4 plate brown rice providing carbs for energy and protein, 1/4 plate seitan for filling protein. vinaigrette on the side to provide healthy fat and flavor.

Liver Reduction Diet

Your liver reduction diet will typically start about two weeks before your bariatric surgery date. This is because it takes about two weeks for the glycogen stores in your liver to be depleted, which decreases the size of your liver. 

To deplete the glycogen stores you will need to follow a low carbohydrate diet. Restricting your carbohydrate intake to 50 g per day is effective to achieve this goal although your bariatric program’s recommendation may differ slightly.

Sometimes it is recommended to use meal replacements and protein shakes, but it is not necessary to use only meal replacements and protein shakes. You can follow a liver reduction diet using a combination of regular food with meal replacements and protein shakes too and does not require you to ‘avoid all carbs.’ 

Your bariatric center may or may not require you to use protein shakes and meal replacements as a part of your liver reduction diet. Using meal replacements and protein shakes can make it easier for you to follow your bariatric pre-op diet. I encourage you to use them as a part of your bariatric surgery pre-op diet even if it’s not required.

During the liver reduction diet you should continue to work on the habits listed above from the initial nutrition intervention.

hands cupped around a liver

What to Eat on a Bariatric Surgery Pre-op Diet as a Vegan

As a vegan you may feel very worried when you look at your bariatric center’s recommendations of what to eat on a pre-op diet. I have heard from many people that their bariatric program did not provide very many recommendations that work for a vegan diet. 

It is possible to stay vegan on a bariatric surgery pre-op diet. 

Whether you’re vegan or not it can be challenging to figure out what to eat on the bariatric preoperative diet. As stated above, you will be encouraged to have balanced meals including a variety of foods during the initial phase of the bariatric preoperative diet.

FREE one day meal plan. click here. photo of vegan bariatric pre op menu

Once you get to the liver reduction diet the recommendations get much more strict to ensure that your liver has reduced down in size enough by the time you have surgery. 

FREE one day liver reduction meal plan. click here. photo of vegan liver reduction meal plan.

Additional Nutrition To Dos While on the Bariatric Surgery Pre-op Diet

Along with working with your dietitian to develop diet habits that will serve you well after bariatric surgery you should also be doing other things to get ready for bariatric surgery. 

Screening for Vitamin and Mineral Deficiencies

Your bariatric program will typically check some laboratory values before bariatric surgery that include some vitamin and mineral levels. This helps to find out if you have any vitamin and/or mineral deficiencies. If you are found to have any deficiencies they will be corrected with prescribed vitamin and mineral supplements.

You will be screened for common vitamin and mineral deficiencies that include iron, vitamin B12, vitamin B1 (thiamin), vitamin D, vitamin A, vitamin E, vitamin K, zinc, and copper. Depending on your bariatric program they may include all or some of these.

If they don’t include all of the ones listed here you can ask for more to be added on for you. Keep in mind that part of the reason they are not all included is that health insurance may not cover for these labs to be checked even though they cover the bariatric surgery.

Learn About the Postoperative Diet Progression

Before you have bariatric surgery it is imperative that you have a thorough understanding of your diet progression after the surgery. Failure to follow your program’s guidelines of which foods to eat when and how much may result in you feeling ill, becoming malnourished, or having inadequate weight loss. 

Typically bariatric programs have a set diet progression that takes about 3 months to get through. The usual stages include:

  • Clear Liquid (about 24-48 hours after surgery)
  • Full Liquid (about 10-14 days)
  • Semisolid/Soft/Pureed (may last 2-3 weeks)
    • There might be just one stage for these 3 and then sometimes it is separated into a few different parts
  • Regular (may start about 4-6 weeks after surgery)

Your bariatric center will probably recommend some variation of the above. There is not enough evidence to support only one way of advancing the diet after bariatric surgery so there tends to be some variation. Please consult your bariatric center for specifics on what is allowed during each stage and when it is okay for you to move from one stage to another. 


Making changes to your diet and habits in preparation for bariatric surgery is not easy for anyone. Whether you’re vegan, vegetarian, omnivore, or somewhere in between making changes to your diet and lifestyle is a lot of work. 

Many will agree though that being vegan adds another layer of complexity for most people looking to have bariatric surgery. This is because most bariatric surgery materials are not designed with vegans in mind. Here at Vegan Bariatric Dietitian it is my mission to change that by providing support and education to vegans undergoing bariatric surgery. 

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Kim, Julie J., et al. “ASMBS updated position statement on insurance mandated preoperative weight loss requirements.” Surgery for Obesity and Related Diseases 12.5 (2016): 955-959.

Weight Management Dietetic Practice Group. Pocket Guide to Bariatric Surgery. Edited by Kellene A. Isom and Melissa C. Majumdar, 3rd ed., Academy of Nutrition and Dietetics, 2022.

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