Gastric sleeve pre op diet: what is it and who is it for?

Chapter 2

Gastric sleeve pre-op diet is basically a 2-week diet to prepare yourself for the surgery. So, you might be wondering, “why would I need gastric sleeve pre op diet? I am already going through this surgery to lose weight, to begin with.”

You’re right. However, when it comes to gastric sleeve surgery diet, you’ll have a pre and post. In this article, we’ll cover everything you need to know about this 2 weeks pre op diet. Let us explain.

Since one of the most important digestive organs is being altered by gastric sleeve surgery, depending on your health situation and BMI, you may need to prepare yourself for the surgery and for the afterward. 

Let’s dive into the details of the pre-op diet.

What is gastric sleeve pre op diet?

It is a 2-week diet before gastric sleeve surgery. You should go easy on your stomach and liver during this diet. You can accomplish the goals of the gastric sleeve pre op diet by following its instructions.

You should increase your protein intake to 60 grams via lean meats and fish, eat fibrous vegetables, and keep your body hydrated. What you shouldnt do is consume caffeine, carbohydrates, sugary foods or drinks, and carbonated drinks. Caffeine can increase appetite and carbonated drinks can cause gas buildup and enlarge your stomach.

You can consume sugar-free products. Such as low-calorie beverages that are also caffeine and sugar-free, sugar-free Jell-O, sugar-free popsicles, low-calorie healthy snacks, etc.

When you are 2-3 days away from your procedure, there will be another change in your diet. You will switch to an all-liquid diet, leaving solid food behind for a while. A gastric sleeve pre op liquid diet will help you prepare for the first two weeks after surgery.

Don’t let the word “liquid” fool you. You will only be drinking clear liquids. Such as chicken or veggie broth, protein shakes, clear tea, sugar-free juices, etc.

gastric sleeve pre op diet

Why diet before gastric sleeve?

“Why diet before gastric sleeve? Am I not supposed to diet afterward?” A gastric sleeve pre op diet can be necessary in cases in which the patient has more than 50 BMI, or they have fatty liver disease.

Gastric sleeve pre op diet will help:

  • improve your digestion,
  • lower the risk of complications,
  • shrink your liver, hastens your healing process,
  • and adjust to your new lifestyle!

Also, your stomach needs to be empty for the procedure. Yes, you should stop eating, drinking, and smoking before 10 PM on the previous day of your surgery. But, if you have been eating a lot of food, which are hard to digest, these can still be present in your stomach.

If you do eat and do not let your surgeon know before getting injected with anesthesia, this can cause unwanted outcomes. To avoid that from happening, we check your stomach’s contents via endoscopy before we apply the anesthesia. If your surgeon detects that you have eaten, they will have to postpone your surgery.

How does the pre-op diet shrink your liver before gastric sleeve surgery?

By following the gastric sleeve pre op diet, your body will use the excess glycogen stored in your liver. As the stored glycogen will be used up, your liver will shrink and get softer. This will make the surgery easier to perform.

How many calories should I be eating on a liquid diet before gastric sleeve?

In order to ready yourself for the gastric sleeve procedure and the post-surgery diet, your calorie intake for the last 2-3 days should be between 1200-1400 calories. You will be getting most of your calories from protein shakes. Of course, you need to get high-quality protein powders in order to obtain good nutrition from your shake.

How long is the pre op diet for gastric sleeve?

So, how long is the pre op diet for gastric sleeve exactly? Ideally, the diet prior to gastric sleeve should be 2 weeks. It may go up to 3 weeks if the patient is way too over the BMI limit or their liver is way too fatty to perform the surgery.

If you were to cheat on your pre op diet for gastric sleeve, your liver may not shrink enough for the surgery to be performed safely and easily. And if you eat too much, you won’t be able to empty your stomach in time. And during the procedure (before injecting you with anesthesia), your surgeon will be able to see if you have eaten or not during the endoscopy. This may end up in postponing your surgery. This means a longer diet is required.

Who should do gastric sleeve pre op diet?

Patients whose body mass index (BMI) is over 50 should go through with this diet. Yes, it is a weight loss surgery, but the risk of complications during and after surgery increases as the BMI increases. Most patients who wish to have this procedure also most likely have fatty liver disease. A fatty liver is an enlarged liver and that complicates the surgery more. So, you should go for an ultrasound and find out whether your liver is enlarged or not. If it is, you are going to need to diet before gastric sleeve surgery.

Why do some surgeons ask for pre op diet for gastric sleeve and some don't?

So, how important is pre op diet for gastric sleeve really? Some surgeons ask their patients to follow this 2-week diet to make both their surgery and post-op diet easier. If the patient’s liver is too fatty, it will be harder to move to reach the stomach. In these cases, the patient’s BMI is usually over 50, and it gets more dangerous as the index gets higher. 

Other surgeons do not require a diet prior to gastric sleeve because it will have little to no effect on the surgery. If the patient’s liver is not too fatty and stiff, with the help of the latest technology equipment, it is easier to handle the liver. Although not required, some patients might want to follow this diet. As long as they are consulting their dietitians and not starving their bodies, they are free to do so. They can do a 7 day pre op diet for gastric sleeve with the same instructions.

I don't want a gastric sleeve, can I still do the pre op diet?

Of course, you can. But should you?

This pre-op diet is to prepare the patients for surgery and/or their post-op diet. Everyone has a unique type of body. So, people who do not wish to go through the surgery should get their individual diet list prepared by a dietitian. If you were to go through with this diet without knowing anything about your body, it may cause harm to your health or might result in you gaining weight.

Let’s say you do this diet. The “liquid diet” is not hard to maintain in the long run. If you were to suddenly go from liquid to solid, you might end up gaining weight. Also, shocking your stomach like that can cause an upset stomach. Your stomach will not shrink in a short period of time. You can malnourish yourself with this diet in the long term if you do it unsupervised.

Your diet should be arranged accordingly to your overall health. For instance, if you have PCOS, there are certain foods you need to stay clear from such as fried food, sugary food, refined carbohydrates, etc. That is why you need to consult a dietitian to get the correct diet for you. Remember, an incorrect diet and starving yourself of necessary nutrients only result in harm. 

FAQ on gastric sleeve pre op diet 

Do you have more questions? We got you! If the question in your mind is not here, feel free to contact us.

Why no caffeine before gastric sleeve?

Caffeine is, sure, beautiful. The smell, the taste… It is great indeed, but it will do no good for you before and long after your surgery. Caffeine dehydrates the body. And for your pre and post-surgery period, you are going to need to stay hydrated. Also, caffeine stimulates the appetite. You might call it an appetizer. And you should start fighting your appetite before the surgery.

When to stop alcohol before gastric sleeve

Your liver needs to relax before the surgery. So, it would be best if you went easy on it. Do not drink at all 2-3 days before surgery. If you do, more anesthesia might be needed. Alcohol tires your liver and dehydrates your body. These can lead to serious complications during and/or after the surgery.

During your 2-week diet, limit your drinking to 1-2 glasses of low-calorie alcoholic beverages such as gin tonic.

When to quit smoking before gastric sleeve surgery

Ideally, you should quit smoking 1-1,5 months before your surgery. If it is currently hard for you to do so, smoke less than you usually do and quit smoking at least 15 days before surgery.

If you still could not quit smoking, not smoking right before and afterward is way more important. Just a gentle reminder, as we’ve discussed previously, the day before your surgery, you should stop eating and drinking. You should also stop smoking after midnight the day before your surgery to avoid nausea before and right after your surgery and other post-op complications.

Congratulations, you are done with this chapter. Now it’s time for Chapter 3 about the post-op diet after gastric sleeve.


(1) Bray GA, Frühbeck G, Ryan DH, Wilding JPH. Management of obesity. The Lancet. 2016;387(10031):1947-1956. doi:10.1016/s0140-6736(16)00271-3 Link

(2) Tabesh MR, Maleklou F, Ejtehadi F, Alizadeh Z. Nutrition, Physical Activity, and Prescription of Supplements in Pre- and Post-bariatric Surgery Patients: a Practical Guideline. Obesity Surgery. 2019;29(10):3385-3400. doi:10.1007/s11695-019-04112-y Link

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