Gastric Sleeve Pre-Op Diet & What Happens if You Cheat?

Gastric Sleeve Pre-Op Diet in Los Angeles, California

Gastric sleeve (laparoscopic sleeve gastrectomy) is a type of bariatric surgery.

Bariatric surgeries represent one of the most effective methods we currently have for reducing body weight and fighting the pandemic of obesity.

The gastric sleeve procedure involves decreasing your stomach size to restrict your food intake. Once your stomach is made smaller by gastric sleeve surgery, you will find yourself eating smaller meals.

You will feel less hungry and fuller faster while you eat.

There are also hormonal changes made during surgery that make it easier to lose weight.

The result of surgery is significant weight loss. Gastric sleeve patients can expect to lose 50% to 60% or more excess weight.

The effectiveness of the gastric sleeve depends on a few factors, one of those being how well you do on the gastric sleeve preoperative-op diet.

The gastric sleeve pre-op diet is laid out below to give you an idea of the changes you need to conform to if you hope to succeed with this life-changing and life-saving bariatric procedure.

What is a Gastric Sleeve?

Gastric Sleeve

The gastric sleeve is the name given to your shrunken stomach. The part of your stomach that remains after surgery is fashioned into a pouch or “sleeve.” The remaining stomach tissue is fully functional, so you don’t lose anything necessary during surgery.

The gastrectomy, the technical name for the stomach sleeve left behind, represents about 15% of your stomach’s original volume. Gastric sleeve surgery is permanent and cannot be reversed.

Why is a Pre-Op Diet Necessary Before Gastric Sleeve Surgery?

Your bariatric surgery places you on a pre-operative diet for several important reasons.

Safer Surgery

The dietary changes made immediately before surgery help to reduce the fatty deposits surrounding the liver.

Easier Surgery

Without all those fatty deposits, your bariatric surgeon can gain better access to the stomach, making for a simpler and faster surgery.

Lowered Risk

The higher your body mass index (BMI), the greater the risks to your health during and immediately after bariatric surgery.

Adhering to a pre-surgery diet is linked with a lowered risk of complications.

Fosters Habit Building

Going on the gastric sleeve pre-op diet starts with the habits you must adopt to make weight control a lifelong commitment.

Succeed with the pre-op diet, and you’ll gain supreme confidence in setting and achieving goals.

Pre-Op Diet Shrinks Your Liver

The primary purpose of the gastric sleeve pre-op diet is to reduce the size of your liver.

You might not realize it, but many morbidly obese individuals suffer from fatty liver disease.

This condition is characterized by fat cells that accumulate in and around the liver. Too much fat can cause the liver to grow in size and function poorly.

Shrinking your liver makes for better surgery. Your surgeon may delay surgery until the liver has reached the appropriate size.

The pre-op diet is a low-sugar, reduced-calorie eating plan that should be followed for fourteen days before surgery.

The exception is , when you switch to a clear, liquid diet two days before surgery. Your bariatric surgery may permit you to consume one no-sugar protein shake daily in addition to water, broth, tea, decaffeinated coffee, Jell-O, and sugar-free popsicles.

On the night before surgery, you are only permitted clear liquids and nothing by mouth (NOP) after midnight.

Following this diet has been shown to shrink the size of your liver, making weight loss surgery safe and easy.

Example of a Gastric Sleeve Pre-Op Diet

Drink Your Liquids

Gastric Sleeve Pre-Op Diet

During the sleeve gastrectomy pre-op diet, drink at least eight to twelve ounces of sugar-free or calorie-free liquids between meals. This should total sixty-four ounces per day unless directed by your bariatric surgeon.

Acceptable drinks on the pre-op diet before gastric sleeve include water, sugar-free Tang, Crystal Light, sugar-free Kool-Aid, fat-free broth, sugar-free popsicles, and sugar-free gelatin.

Breakfast Menu

Drink a High Protein Meal Replacement Shake (8 to 12 ounces), less than two hundred calories, less than 15 grams of protein, and less than 5 grams of sugar.

High protein shakes can come from Carnation Instant Breakfast mixed with skim milk or 1% milk, DiabetiTrim from Sam’s Club, the Atkins Advantage Shake sold at Walgreens and Walmart, and Designer Whey sold at CVS, Target, Walgreens, and Walmart.

Ask your bariatric surgeon to suggest other high-protein shakes to give you variety in the days leading up to your gastric sleeve weight loss procedure.

If you are lactose intolerant, let your bariatric surgeon know. You can drink alternative replacement shakes as part of your pre-op diet. You may also take a lactase enzyme with your cottage cheese if bloating and gas become an issue.


Drink a High Protein Meal Replacement Shake (8 to 12 ounces) and one piece of fruit, such as a pear, apple, or tangerine.

Afternoon Snack

Choose one of the following:

  • Two ounces of deli meat
  • ½ pack of tuna
  • Low-fat beef jerky
  • One string cheese
  • Light yogurt (6 to 8 ounces)
  • Light yogurt smoothie (less than 90 calories)
  • ½ cup nonfat cottage cheese


  • One cup of non-starchy vegetables without oil or butter (raw or cooked)
  • Four ounces of lean meat (roast beef, lean pork, chicken breast, ham, or fish)
  • One slice of low-calorie whole-grain bread or two tablespoons of pasta, rice, beans, or potato (Optional)

Evening Snack (Optional)

A man's hand holding a red apple.
  • ½ of an apple or ten baby carrots


The pre-op diet should NOT include gravy, BBQ, other sauces, butter, oil, grease, salad dressing, mayonnaise, peanut butter, ketchup, or breaded foods. For taste, spritzing your salad with salad dressing can be acceptable.

You’ll also note that no sodas, sweet teas, lattes, or fruit juices are on the gastric sleeve pre-op diet. Those must be cut out entirely if you want the most success after bariatric surgery.


Your bariatric surgeon will advise you to take vitamins and other nutrients to supplement the pre-op diet and give your body what it needs to be healthy.

One popular supplement regularly advised as part of a pre-op diet is the calcium tablet (600 to 1200mg daily).

Get Ready for the Post-Surgery Diet

The gastric sleeve pre-op diet sets the stage for adopting healthier habits. These habits are necessary for finding long-term success with bariatric surgery.

After surgery, you will follow the gastric sleeve post-op diet.

For the first week following your procedure, you’ll continue consuming clear liquids as you did in the days preceding surgery. This clear liquid diet helps to avoid postoperative complications, such as gastric leakage, bowel obstruction, dehydration, constipation, and diarrhea.

Drinking clear liquids also gives your body time to heal. The post-op diet will contribute to adequate healing as well.

During this time, drink plenty of clear liquids. Try not to drink anything containing sugar. Consuming sugar as a gastric sleeve patient can leave you open to suffering from dumping syndrome.

What is Dumping Syndrome?

This condition is common in bariatric surgeries and occurs when sugar enters the small intestine too rapidly. This sometimes results in stomach upset, fatigue, diarrhea, and vomiting.

Another reason to stay away from sugar is that it’s filled with empty calories. Try to minimize or eliminate sugar from your diet now and in the future for the most long-term success.

During week two, after gastric sleeve surgery, you will be placed on a full liquid diet, where you will find yourself consuming protein shakes, instant breakfast drinks, and thin broths or soft soups. You can also drink unsweetened milk, sugar-free, nonfat pudding, nonfat plain Greek yogurt, hot cereal (thinned), and sugar-free sorbet or ice cream.

During week three, you will add pureed foods to your daily diet. For best results, reintroduce foods to your diet slowly and chew slowly. You’ll want to masticate each bite to get every vitamin and nutrient from your healthy foods. Ideally, you’ll want to chew your food at least twenty-five times if you can.

Suitable foods during week three include soup, cottage cheese, mashed bananas, cooked white fish, and silken tofu.

In the fourth week, you can introduce solid foods to your diet. Stick to healthy foods like well-cooked chicken, vegetables, sweet potatoes, fruit, low-sugar cereal, and low-fat cheese.

Avoid pasta, high-carb options, and white potatoes to maximize your weight loss one month post-gastric sleeve surgery.

How to Stay on Track with Your Pre-Op Gastric Sleeve Diet

A plate of salad with tomatoes and a wooden spoon.

Remember Why You’re Doing It

When you’ve taken the time to research and prepare for a major procedure like the gastric sleeve, you should want everything to go off without a hitch.

Keep your surgeon’s recommendations and valuable time in your thoughts. Not adhering to the pre-op diet can hinder your health and may delay surgery for safety reasons.

To stay on schedule and convey to your surgeon that you are committed to success, do your best to stick with the pre-op diet, no matter what.

Plan and Shop Ahead

Before the day of surgery, grocery shop for all the protein shakes, low-calorie drinks, and other items you will need for your pre- and post-op diets.

Not having the drinks and food you need can lead to cheating. Set yourself up for success by preparing for your upcoming dietary changes.

Surround Yourself with Support

Drinking your meals can be challenging, and two weeks can seem like an eternity when all you want is solid food. Keep yourself on track by joining a support group in your area or online. Friends and family can also help you remain stable when the pressure to break your pre-op diet becomes overly strong.

Move Your Body

Exercise doesn’t have to be boring and grueling. Search for dance, martial arts, or other lessons you may be into on YouTube. Video instruction for twenty to thirty minutes can improve your physical health and well-being. Increasing your heart rate will also help to curb your cravings.


Clearing your mind and shutting out the world for ten to fifteen minutes can do wonders for mentally centering you. Try to meditate daily or every other day, particularly when your food cravings are strongest.

Find Delicious Diet Options

Just because you are placed on a gastric sleeve pre-op liquid diet doesn’t mean you must consume gruel. Ask your bariatric surgeon about smoothies with favorite fruits, vegetables, and protein powders. Don’t be afraid to try new things. You may find you crave your liquid meals during the pre-op phase.

Gastric Sleeve Pre-Op Diet: What if You Cheat?

A person holding a burger with fries on a plate.

As a human being, you are not perfect. Cravings, stress, and other factors can contribute to cheating on your pre-op diet. It happens.

If you break from the pre-operative diet plan, your liver will not shrink enough to make surgery safe and simple.

Your bariatric surgeon would know within minutes if you cheated. The laparoscopic camera can pick up food you may have eaten during surgery. The food could be in your stomach or intestinal tract. Having food present can leave you open to infection.

With an increased risk of complications and an inability to commit to a healthier diet, your surgeon may cancel your surgery altogether.

Sticking with the gastric sleeve pre-op diet for the full duration is best. Doing so will make creating healthier habits you must adhere to easier after your bariatric surgery.

Why Patients Tend to Cheat on Pre-Op Diets

You are more likely to cheat on the pre-op diet before gastric sleeve surgery if you:

  • Lack of a solid support system
  • Don’t know how to eat properly
  • Can’t seem to say no to your cravings
  • Aren’t motivated enough to change

Knowing these facts can help you prepare for a successful future with your preferred bariatric procedure.

Before you begin the gastric sleeve pre-operative diet, gather a support system, educate yourself on how to become healthier, and find those things that motivate you to lose weight and keep it off for good.

Most of all, speak to your bariatric surgeon about your struggles with mental health, cravings, and choosing which foods are best for you while you prepare to lose weight with the gastric sleeve.

What to Do If You Already Cheated on Your Pre-Op Diet?

Let’s say you went out and had a big meal in the weeks preceding the scheduled day for surgery. What do you do then?

The first thing is to tell your bariatric surgeon. Your surgeon will want to reschedule surgery to give your liver enough time to shrink in size.

However, your surgeon may not want to reschedule. Decisions such as these are handled on a case-by-case basis.

Once you have informed your surgeon of your mistake (because you are human), get back on the horse.

Find liquid shakes you enjoy the taste of. Stock your fridge and pantry with healthy snacks you can reach for when hungry. The less temptation you surround yourself with, the easier it’ll be to stick to the gastric sleeve surgery pre-op diet.

Sticking with the diet will start you on the path to significant weight loss, ideally for life.

Learn more about gastric sleeves and other bariatric procedures by scheduling a consultation with Dr. Babak Moeinolmolki of Healthy Life Bariatrics in Los Angeles, California. Call our office today.

Dr. Babak Moeinolmolki
December 13, 2021

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