Weight loss surgery diet: what to eat before and after bariatric surgery?

Added by Klaudia Grabowska on 12.10.2020

Weight loss surgery diet

The weight loss surgery diet is the most important part of the bariatric surgery plan. Bariatric surgery itself does not make people slim and healthy, it is just the perfect tool that guarantees the healthy and significant weight loss providing that patients follow a post-op diet and change their lifestyle for the rest of their lives. The idea of weight loss procedures is making the stomach smaller, decreasing its capacity, and modifying the hunger hormone – these factors make it much easier for people to lose weight, but without their commitment and determination especially regarding diet and exercising, the surgery is pointless. 

salmon on white plate with vegetables

The most important part after bariatric surgery is a good diet which is followed, then the weight loss results can be expected

The most common bariatric surgeries are: gastric sleeve, gastric bypass, gastric band, and gastric balloon. Patients are always provided with a special diet plan by a bariatric surgeon and a dietician. Such a diet may vary depending on the surgery type, however, there are some general guidelines regarding the diet before and after bariatric surgery which we describe below.

Diet before weight loss surgery

Pre weight loss surgery diet is the first stage of a bariatric surgery program. It is extremely important that a patient follows such a diet because it is the factor deciding whether a surgeon agrees to perform the surgery or not.

The main reasons why patients must keep a diet for quick weight loss before surgery are as follows:

  • it reduces the risk of surgery complications and side effects
  • it prepares a patient for the major diet changes after the surgery
  • it reduces the amount of glycogen, fat, and water in the liver (when the liver is too fatty and cannot be put aside to disclose the stomach, the surgery is ceased).

So, generally, diet before weight loss surgery is a prerequisite for the surgery. Its time may vary depending on the patient’s weight. Sometimes such a weight loss surgery pre-op diet lasts only 2 weeks, but there are situations when patients need to follow it for months. The decision belongs to the bariatric surgeon and the duration of weight loss before surgery diet depends individually on the patient. 

Hands showing diet balloons word

The right diet after weight loss surgery is crucial to gain effects


The general guidelines for preoperative diet for weight loss surgery include:

  • drinking at least 2 liters of fluids a day
  • avoid smoking and drinking alcohol
  • eating regularly (3 main meals and 2 snacks at regular intervals)
  • staying as active as possible.

What to eat before the weight loss surgery

Generally, patients need to follow a low carb diet before weight loss surgery, which involves 800-1000 kcal only. Those who are suggested to follow a pre-op diet for more than 2 weeks may be allowed to eat 1200 kcal at the beginning, but in each case, a 2-week diet before weight loss surgery should not exceed 1000 kcal. The amount of carbohydrates that patients can eat is 100g daily, besides, the diet is low in fat and moderate in proteins.

The portions of macro components and products are:

  • carbohydrates: 3 portions a day
  • proteins: 2 portions a day
  • fruits: 1-2 portions a day
  • vegetables: 4-5-portions a day
  • diary products: 1-2 portions a day.

The diet before weight loss surgery changes into full liquids 2 days before the procedure – patients should eat e.g. vegetable puree soups, broth, protein shakes. 1 day before the surgery, only clear liquids are allowed, and about 2 hours before the surgery, patients should not eat or drink anything. 

Diet after weight loss surgery

Post weight loss surgery diet is composed individually by a clinic dietician and the surgeon. It consists of 5 stages and patients need to keep the stages frames and products allowed very carefully to avoid gastric problems.

What to eat after bariatric surgery?

Weight loss surgery post op diet stages are as follows:

Stage 1: Clear liquid diet ( up to 2 weeks after the surgery)

You can take only liquids on the first day like water, and on the next day, you are allowed to consume more nutritious liquids, for example, milk. As you need to be constantly hydrated, you should drink a lot. However, during the very first days, you can try drinking dilute fruit juices just to keep away from nausea or diarrhea.

After you get used to those, you can introduce other liquids like :

  • Broth
  • Unsweetened juice
  • Decaffeinated tea or coffee
  • Milk (skim or 1 %)
  • Sugar-free gelatin or popsicles

Stage 2: Liquid diet (2-4 weeks following the surgery)

pureed food

4 weeks after the surgery the patient can introduce a pureed diet which consists of pureed foods, which may be prepared with the use of a food processor or a blender

During the first weeks after the procedure, your priority should be helping your body to heal, thus you should pay attention to avoiding complications after the surgery. During the first days, dietary guidelines after bariatric surgery allow you to drink a small number of clear liquids so that your stomach will heal properly and will not be stretched by food. After that, you may start to incorporate other liquid types like blended thin soup or broth, sugar-free pudding or non-sugar and fat yogurt, low-fat cottage cheese.

Stage 3: Pureed food (4-6 weeks)

Generally, four weeks after the surgery are enough to include a pureed diet which consists of pureed foods (a type of food which may be prepared with the use of a food processor or a blender) which have a thick, pudding-like consistency. Moreover, it is important to keep away from spicy seasoning which may cause stomach irritation. Also, fruits that contain seeds like strawberries or kiwi cannot be eaten at this stage and some foods which are too fibrous to liquefy like broccoli or cauliflower. You are allowed to eat from three to six meals a day and each of it ought to be no larger than 4 to 6 tablespoons. Bear in mind to eat slowly.

You may eat these following food:


  • Hands showing diet balloons word

    Fresh fruits without seeds are a good choice at this stage of diet

    apples or applesauce

  • bananas
  • canned fruits
  • peaches
  • apricots
  • pears
  • pineapples
  • melons


  • tomato juice
  • spinach
  • carrots
  • summer squash
  • green beans


  • yogurt
  • white fish (cod, tilapia, haddock)
  • cottage cheese
  • ricotta cheese
  • beef
  • chicken
  • turkey
  • scrambled eggs

Stage 4- soft diet (6-8 weeks after the surgery)

During the first few weeks of the diet after weight loss surgery you are obliged to eat pureed food and after you gain permission from your doctor you may introduce a soft food diet after bariatric surgery. You may eat three to five meals a day where each portion should measure ⅓ to ½ cup of food. Remember to chew properly each bite before swallowing.

The food you may include in your diet:

  • soft-boiled eggs
  • ground meat
  • cooked white fish
  • cottage cheese
  • cooked or dried cereal
  • rice
  • canned fruits without skin, such as peaches or pears
  • cooked vegetables, without skin

Stage 5: stabilization ( 8 weeks after the surgery)

During the last stage of weight loss surgery, diet is the introduction of solid foods, however, you would need to chop or dice them into small pieces as large portions may cause a blockage which leads to pain, nausea, or vomiting. Thanks to the gradual introduction of food you may notice which can be tolerated by the stomach and which food you should get rid of.

You should not eat food which is difficult to digest, for example:

  • fibrous or stringy vegetables (such as pea pods)
  • popcorn
  • corn on the cob
  • carbonated beverages
  • tough meat
  • fried food
  • crunchy foods (such as pretzels, granola, seeds, and nuts)
  • dried fruit
  • bread and bread products

In order to keep a reasonable level of mineral absorption and vitamins, the patient requires a large dose of multivitamins like iron, folic acid, etc.

Approximately, for months following the surgery, you should be allowed to eat regular food. Nevertheless, you should keep track of portions and pay attention to nutrition after the bariatric procedure. Your meals should be rich with fruits, vegetables, lean proteins, and carbohydrates. Vitamins and minerals supplementation cannot be ruled out particularly in case of gastric bypass, sleeve, and POSE surgeries. In order to keep a reasonable level of mineral absorption and vitamins, you would probably require a large dose of multivitamins (like iron, folic acid, copper, zinc, and selenium), calcium, Vit D, and Vit B complex. Regarding weight loss procedure, it is not about shying away from specific food but it is all about making changes in your diet completely. Thus, you should eliminate foods rich with fat and carbohydrates.

Vegetarian and vegan diet for weight loss surgery

Vegetarian diet after weight loss surgery and vegan diet after weight loss surgery are practiced by many people and in fact, there are no contraindications regarding a meat-free diet after bariatric surgery. The main issue here is to provide yourself with enough proteins and microelements. 

The food with a high percentage of proteins includes:

  • vegetables (spinach, broccoli, lettuce, cauliflower, tomato
  • beans (kidney beans, soybeans, lentils)
  • mushrooms
  • eggs
  • dairy (yogurt, cottage cheese)
  • nuts
  • whole grains and seeds.

Vegan diet is more demanding in maintaining the recommended protein intake because proteins are not complete. In this diet, any animal-related food is avoided – it concerns not only meat but also eggs, dairy, or honey.

Vegan patients should look for proteins in:

  • soybeans
  • tofu
  • soy milk
  • protein shakes
  • vegetables
  • whole grains and seeds.

The biggest concern for vegan patients is Vitamin B12 deficiency, so it needs to be supplemented all the time. If you are vegan or vegetarian, you should inform your clinic about it so that they can modify the post-op diet plan to meet your way of living. Also, the supplements composition may vary for vegetarians, vegans, and patients eating meat.

Ketogenic diet after bariatric surgery

fish with broccoli

The ketogenic diet is restrictive as only meat, fish, seafood, healthy fats, low-carb dairy foods, non-starchy vegetables are allowed. Grains, fruits, starchy veggies, legumes, high-carb foods, and sugar are prohibited in this diet

“Keto” is an abbreviation from ketogenic which relates to a metabolic state when your body functions on ketones produced by the liver but not on glucose and insulin. The ketogenic diet after bariatric surgery helps the change and preservation of the metabolic state. On the whole, when the body receives an appropriate amount of carbohydrates it works on glucose which is a main source of energy. During the keto diet which has low carbs and sugars, the liver generates ketones from the fats which boosts the body, thus you start to lose weight. Although, the keto diet may be a huge change in your lifestyle, according to studies that there are more pros than cons. For example, improvement in mood, more energy, blood sugar in control, mental clarity, hunger in control, lowered blood lipid level, and blood pressure.  Not always keto diet is a solution for everyone as this type of diet is restrictive as only meat, fish, seafood. healthy fats, low-carb dairy foods, non-starchy vegetables are allowed. Moreover, there are certain types of food that are prohibited like grains, fruits, starchy veggies, legumes, high-carb foods, and sugar.

During the first stage, you may encounter side effects like fatigue, headaches, muscle cramps, constipation, smelly breath, dizziness as a result of dehydration and an insufficient amount of electrolytes.

Generally, the proportion of macro is as follow:

  • 70% fats
  • 25% proteins
  • 5% carbohydrates

For example in 1000 kcal diet a day the ratio is as follow:

  • 70% fat= 700 calories/78 grams fat
  • 25% protein= 250 calories/62.5 grams protein
  • 5% carbohydrates= 50 calories/12.5 grams carbs

Nevertheless, some issues ought to be taken into consideration when choosing a keto diet. For example, it is recommended to eat at least 60 to 80 grams of proteins a day, however, many people do not tolerate such amount of fat daily.

Thus, the keto diet may look like this:

  • 80 grams protein (320 calories) = 32% of total calories
  • 20 grams NET carbohydrates (80 calories) = 8% of total calories
  • 67 grams fat (600 calories) = 60% of total calories

After modifications, the keto diet may resemble a low carb diet, thus, you may try to eat less than 40-80 grams carbs a day instead of 20. According to some patients, they stated that after reducing the intake of carbs they had more energy, hunger control was improved, blood sugar was lowered, lost weight, and experienced better mental focus. Considering weight loss following the bariatric surgery it is of great importance to include nutrients into a well-balanced diet. Although it may not be a good option for those who underwent gastric bypass or sleeve, it may turn out to be a great choice for those who had gastric plication or gastric balloon. Moreover, keto diet is not suitable for those with Type 1 Diabetes or Type 2 Diabetes and pregnant women.

Liquid diet for weight loss surgery

Liquid diet after weight loss surgery is an extremely important stage in the diet plan. The time of a liquid diet is a recovery period for the body and stomach. The body learns how to tolerate and digest food after the surgery, so it should not be burdened by solid or even soft food at this stage. The liquid diet after bariatric surgery lasts for 4 weeks on average, but each patient should start adding some more solid food only when he/she feels ready for it. Besides, patients must follow a liquid diet to lose weight before surgery. The diet components and course are the same for the pre-op and post-op period, only the amount of liquids that are acceptable is modified by a dietician. Generally, a liquid diet for weight loss surgery is a very difficult period for patients, as it is an abrupt, sudden change, however, it is inevitable to avoid any side effects after the surgery, get prepared for the future change of eating habits, and achieve the weight loss results.

High protein foods after bariatric surgery

Regarding the post-op diet, all the necessary information will be provided by your surgeon. It is of great importance to stick to the diet so that the recovery period and weight loss results are successful. Although restrictions may be strict, you need to make sure that your daily intake of proteins is suitable so that the body receives nutrients enough. Most importantly,  proteins are responsible for building cells, tissues, and organs, however, they are broken down thus they need to be replaced. Also, you should bear in mind, that any bariatric surgery is not a magical solution for obesity, thus, you need to follow your workout regime. The surgery is about 50% of success, and apart from that 50% is following your diet strictly and starting exercising regularly.

Your diet will dramatically change following the surgery, thus, you need to pay attention that you chose a well-balanced diet full of nutrients that are beneficial for your well-being and also may help with problems of overeating. Another essential aspect is high protein foods after bariatric surgery. You can find them in eggs, meats, fish, tuna, seafood, soy milk, yogurts, cottage cheese, and milk products. The daily need is from 65 to 75 grams, yet do not worry if you cannot reach this goal straight after the surgery.

Raw chicken breast food photography recipe idea

Chicken breast contains low calories and high nutrients

In order to get used to a large number of proteins you may:

  • eat proteins first so that you will feel full quickly
  • eat proteins which contain low calories and high nutrients ( like grilled chicken or turkey)
  • start supplementing proteins or/and protein shakes in order to keep the diet in balance.

Weight loss surgery diet summary

Summarizing, a diet before and after a bariatric surgery plays a key role in the whole process of losing weight. The pre-op diet makes patients prepared for the surgery and shows them what to expect afterward. The main assumption of pre-op diet is reducing the fat around the liver to make the surgery possible at all. The post-op diet is the most demanding, challenging, but also satisfying time because the strict following of the post-op diet brings quick and impressive results of weight loss. In case of any digestive problems, doubts regarding the food or products, or questions about the diet, patients should contact their dietician or bariatric surgeon for advice and instructions. Once patients achieve the final results, they should still follow a healthy and balanced diet and exercise regularly to avoid weight gain in the future. It should not be treated as a diet anymore, but rather as a conscious and healthy diet and lifestyle choices. 

The ketogenic diet is restrictive as only meat, fish, seafood, healthy fats, low-carb dairy foods, non-starchy vegetables are allowed. Grains, fruits, starchy veggies, legumes, high-carb foods, and sugar are prohibited in this diet


NHS Choices, NHS, www.nhs.uk/conditions/weight-loss-surgery/afterwards/.

“Post Bariatric Surgery Diet & Nutrition.” UPMC, www.upmc.com/services/bariatrics/surgery-process/post-surgery/diet.

Richardson, William S, et al. “Long-Term Management of Patients After Weight Loss Surgery.” The Ochsner Journal, The Academic Division of Ochsner Clinic Foundation, 2009, www.ncbi.nlm.nih.gov/pmc/articles/PMC3096273/.

Staff, written by OC. “The Big Gastric Bypass Diet Guide.” Obesity Coverage, www.obesitycoverage.com/the-big-gastric-bypass-diet-guide/.

UCSF Health. “Dietary Guidelines After Bariatric Surgery.” Ucsfhealth.org, UCSF Health, 19 Aug. 2020, www.ucsfhealth.org/education/dietary-guidelines-after-bariatric-surgery.

Klaudia Grabowska

Klaudia started to work for Clinic Hunter many years ago, just after graduating from the John Paul II Catholic University of Lublin in Poland and since that time, this job has become her biggest passion and inspiration.

She has gained necessary expertise and experience by serving patients from all over the world (mainly the UK, Scandinavian countries, and the USA), taking an active part in numerous live and video trainings with clinics in Poland, Hungary and Turkey, participating in international medical tourism conferences and events, and completing internal Clinic Hunter courses. Now, Klaudia is an accomplished patient advisor specialising in such fields as dentistry, plastic and bariatric surgery and hair loss treatment. Her main idea is helping people nad making their lives better, that is why this job brings her so much satisfaction and joy.

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