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Following A Liquid Diet Before Bariatric Surgery

Following A Liquid Diet Before Bariatric Surgery

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      You carefully considered the benefits and drawbacks of bariatric surgery, went through the initial medical evaluation, made changes to your diet, and are finally ready for surgery... almost. Your surgery team tells you that you must follow a liquid diet for 2 weeks prior to surgery. This liquid diet before bariatric surgery will continue after surgery as well.

      What is this liquid diet all about and how can you follow it? In this article, we will explore the concept of following such a diet before surgery and provide tips on how to be successful with it.

      Why is a liquid diet needed for bariatric surgery?

      The purpose of a liquid diet before bariatric surgery is not simply to place another roadblock in front of you; instead, it’s to make sure the surgery goes as smoothly as possible. Typically, this liquid diet is done for about 2 weeks just before the date of surgery. The diet accomplishes three main goals:

      • Jumpstarts weight loss
      • Reduces the liver size
      • Prepares you for liquid diets after surgery

      A liquid diet will usually be needed before and after surgery, but this can include a variety of foods.

      Jumpstarting weight loss

      The most popular bariatric surgeries: the roux-en-y gastric bypass and the gastric sleeve procedure, can help people lose about 60-80% of their excess weight. Most of this weight loss occurs in the first year after surgery through a combination of factors that generally include reducing stomach size, appetite, and absorption of nutrients.

      A liquid diet is generally very low in calories, about 800-1000 calories per day, which can help you lose about 4-5 pounds before surgery. This initial weight loss is easier to keep off after surgery as you will get used to eating a much smaller amount of food.

      Reducing liver size

      The liver is a large organ located right above the stomach that is in charge of processing nutrients and breaking down toxins.

      The pre-surgery liquid diet is designed to be low in not just calories, but also fats and sugars. Since the liver is not as active in processing these nutrients, it will temporarily shrink in size. In addition, fat accumulates directly on the liver itself (this results in fatty liver disease over time). Reducing calories on a very low-calorie diet, such as the liquid diet prior to bariatric surgery , will help to reduce this liver fat.

      Reducing the size of the liver is important because it allows better access to the stomach during surgery. This means that the surgery is safer, quicker, and easier for the surgeon.

      Diagram of digestive system
      Notice how the liver (upper left) overlaps with the stomach (upper right)

      Preparing for liquid diets after surgery

      Another benefit of the pre-surgery liquid diet is to get used to following a liquid diet as it will also become necessary after surgery. Typically, you will need to slowly advance from a clear liquid diet composed mostly of broths, water, and sugar-free juice and gelatin to a full liquid diet that is similar to the pre-surgery diet. Making sure you have beverages on-hand and have experimented with what fluids you prefer will make this transition much smoother.

      What does a pre-surgery liquid diet look like?

      A proper pre-surgery liquid diet is typically between 800-1000 calories, 70-120 of protein, low in simple sugars and fat. The exact diet composition may vary depending on which facility you have the surgery at, some facilities prefer a strict liquid-only diet while others will allow small snacks or meals. Your nutrition needs also vary and your medical team will give you individualized recommendations.

      Because the diet consists of a very small amount of food, it is important to get enough protein; and in a liquid diet, this is best accomplished through the use of protein shakes. The key with protein shakes is to choose a variety that has about 15 or more grams of protein and less than 5 grams of sugar per serving. Many products can fit this mold. A protein shake that is too low in protein will not be able to meet protein needs without going over in calories or sugar.

      A variety of other liquids are acceptable, including strained soups and hot cereal. Focus on low sugar and low-fat choices and make sure to stay hydrated with water and sugar-free beverages. Aim for at least 64oz of fluids.

      Finally, a multivitamin is recommended to make sure you are covering all your nutrient bases. A chewable multivitamin is often used after surgery, and it is a good idea to try these out prior to surgery.

      Protein shake
      Protein shakes are the foundation of a liquid diet

      Sample foods allowed

      While technically not completely liquid, foods such as oatmeal are allowed on a liquid diet

      Example pre-surgery liquid diet


      • Protein shake (20g protein, 4g sugar)
      • 6oz plain Greek yogurt
      • 16oz water


      • Protein shake (20g protein, 4g sugar)
      • Sugar-free gelatin
      • 4oz low sodium cream soup without chunks
      • 12oz sugar-free flavored water


      • Protein shake (20g protein, 4g sugar)
      • 8oz skim milk
      • 4oz low sodium broth-based soup


      • 6oz plain Greek yogurt
      • 24oz additional water or sugar-free flavored drink
      • 1 chewable multivitamin

      Nutrition information: 800 calories, 100g protein

      Lemon water
      Keep beverages as low in sugar as possible, infusing lemon can help provide flavor

      Tips to make the liquid diet work

      Between pre and post-surgery requirements, you will need to follow a liquid diet for 4 weeks or more. This will take some getting used to, but the following tips can help:

      1.  Read the nutrition facts label. The nutrition labels will help you estimate the total calories of your liquid diet and ensure you are meeting your protein needs, while avoiding too much sugar.

      2.  Space out meals and snacks. Eating everything at one time will make it harder to manage hunger throughout the day and will cause stomach problems after surgery.

      3.  Avoid restaurants. Very few things on the menu will be acceptable choices and it will only make it more difficult to stay on the diet.

      4.  Stick to a grocery list. It is much easier to have self-control once per week at the grocery store then to try to avoid tempting foods all week.

      5.  Focus on the big picture. Remember the reason you are choosing to undergo surgery and that liquid diets are ultimately temporary.

      Woman grocery shopping
      Do not grocery shop when hungry, make sure you have a plan


      Many surgeons require a special pre-op liquid diet before bariatric surgery that lasts about 2 weeks. The purpose of this diet is to start losing weight, get used to liquid diets, and reduce liver size. These factors ultimately help to ensure the best surgery outcome.

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        Michael Fornaris, RD, CDE


        Michael is a registered dietitian & diabetes educator currently working in outpatient nutrition counseling. He specializes in weight management, diabetes control, prediabetes, and metabolic syndrome.

        Gintas Antanavicius, MD, FACS, FASMBS


        Dr. G is a co-founder of BariBuilder. A US-based expert surgeon with over 10 years of bariatric experience, he regularly publishes research in medical journals like SOARD, Obesity Surgery, etc.