Skinny woman in the middle advising her friends about the right pre-gastric bypass diet

The Pre Gastric Bypass Diet: What To Eat and Drink

If you’re preparing for a gastric bypass surgery, it’s important to follow the pre gastric bypass diet to a T. Deviating from this expertly laid out nutritional plan can cause complications with your procedure, or even prevent you from having your procedure in the first place!

So that begs the question: What IS the pre gastric bypass diet? And how to make sure you’re following it correctly?

In this article we will examine what the pre gastric bypass diet is, why it exists, what you can and cannot eat, and how to get the most out of your diet plan. 

What is the pre gastric bypass diet?

The pre gastric bypass diet is a diet designed to reduce the size of your liver before undergoing bariatric surgery. It typically consists of high-protein, reduced-calorie foods, and will consist of only liquid foods for two weeks prior to surgery.

This special diet helps to reduce the risk of complications from bariatric surgery, and also helps patients to lose weight faster after the procedure.

The pre gastric bypass diet is a safe and effective way to help prepare for bariatric surgery, but it can be difficult for some people to stick with. It’s important to consult a healthcare professional or nutritionist before starting the diet to make sure you’re getting all the vitamins and minerals your body needs. 

On the pre-op diet for gastric bypass, individuals should aim to consume between 700-800 calories per day.

Doctors recommend that patients continue following the gastric liquid diet after gastric bypass, but it’s important to understand that the bariatric liquid diet should not be followed indefinitely. This type of diet should only be used for a short period of time until your body begins to heal. 

This will help to ensure that you receive the nutrients you need for optimal health and prevent any long-term nutritional deficiencies from occurring.

Potential side-effects of the pre gastric bypass diet

When you are doing the pre-op diet for gastric bypass, you may experience a few unwanted side effects. Don’t worry, these side effects are not dangerous, and can be worked through with the help of your doctor. Possible pre gastric bypass diet symptoms include:


One of the most common side effects that individuals may experience when following a pre-op diet for gastric bypass is fatigue. This can be due to a lack of energy as your body adjusts to consuming less calories than it is used to. 

You may also find yourself feeling lightheaded or dizzy due to low blood sugar levels. To help combat these feelings of fatigue, make sure you are getting enough rest.


Another potential side effect that may occur while on a pre gastric bypass diet is constipation. Due to the reduced calorie intake, as well as lack of fiber in the liquids you consume, your digestive system can become sluggish and cause hard stools.

Try to incorporate more fiber-rich foods into your pre-surgery diet to help combat this, and talk with your doctor if you are experiencing any severe constipation symptoms.


Some individuals may experience nausea while following the pre gastric bypass diet. This is due to the increased amount of liquids consumed, as well as the lack of fiber and other nutrients. 

To help combat nausea, try to space out your liquid meals throughout the day and avoid consuming too much at once. You should talk with your doctor if you are experiencing severe nausea.


Headaches can also be a common side effect of following a gastric bypass diet before surgery. This is due to the sudden decrease in calorie intake and lack of certain nutrients that your body may become accustomed to. 

To help reduce the occurrence of headaches while on a pre gastric bypass diet, make sure you are drinking plenty of fluids throughout the day and incorporating nutrient-rich foods into your diet.

What can you eat in the pre gastric bypass diet?

There are clear guidelines of what you can and cannot eat before your gastric bypass surgery. While these guidelines may vary slightly from person to person, you will generally be asked to:

  • Eliminate or reduce intake of saturated fats (fatty meat, whole milk products, fried foods)

  • Eliminate or reduce intake of foods of carbohydrates (sugary desserts, potatoes, pasta, bread)

  • Eliminate juice, soda, and other high-sugar beverages

  • Avoid binging and practice portion control

  • Avoid alcohol

Once you move into the liquid portion of your pre-surgery diet, you should drink plenty of water and stick to eating:

  • Low-sodium broths
  • Sugar-free beverages (non-carbonated)
  • Sugar-free popsicles
  • Sugar-free gelatin
  • Caffeine-free coffee and tea
  • Protein shakes & supplements (At least 60-80 grams of protein per day)

As a general guideline, it is recommended to drink five protein shakes a day and at least 64 ounces of sugar-free liquids to ensure you meet your nutritional needs. 

The importance of protein in pre gastric bypass diet

Protein is an essential macronutrient that plays a critical role in maintaining healthy body functions, including muscle health and weight management. Protein also helps to create new tissue and maintain muscle mass, which can help you sustain muscle and aid weight loss following bariatric surgery. 

Eating enough protein in your pre gastric bypass diet will help ensure your body has the nutrients necessary to heal and recover following the procedure.

When following a pre gastric bypass diet, protein should make up at least 25 percent of your daily calories. Because the amount of food you can eat will be limited after bariatric surgery, it's important to consume enough protein pre-surgery to ensure you are getting the nutrients needed for good health. 

Good sources of protein include lean meats, poultry, fish, eggs, nuts, and protein shakes.

Eating plenty of protein as part of your gastric bypass diet before surgery can also help reduce hunger pangs between meals by keeping your blood sugar levels steady. 

Protein has a slow digestion rate, which helps you stay full for longer and prevents overeating. In addition, adequate protein intake can help speed up your metabolism, making it easier to lose weight.

What is the best protein to take for a gastric bypass?

Now that you know that you need to stay topped up with protein after your surgery, let’s take a look at what qualities you need to look for in your pre gastric bypass diet protein shake.

A protein that helps with healing

Gastric bypass surgery can sometimes prove a little traumatic for your body. Following surgery, doctors recommend that you rest up and let your body heal - and wouldn’t it be great if there was a protein powder for bariatric patients that could help with that?

Fortunately there is!

Collagen protein powder is able to improve gut health, and numerous studies have touted collagen wound healing benefits. As such, topping up with collagen before your surgery (and continuing to use it after surgery) can help you heal up as quickly as possible. 

A protein that is hypoallergenic

Some protein powders can cause allergic reactions, and this is exactly what you DON’T want leading up to a surgery. Make sure your protein supplement has a hypoallergenic formula!

And, since you’re going to be drinking protein shakes after surgery as well, we recommend one that is dairy-free. That’s because many bariatric patients find themselves developing lactose intolerance after surgery - which means whey protein might be a bad idea. 

Collagen is a winner here. It is hypoallergenic, and may even play a part in reducing some reactions, as it can heal leaky gut.

A protein with a complete amino acid profile

Amino acids are the building blocks that make up proteins. All proteins contain different combinations and amounts of these essential compounds, and getting a complete amino acid profile in your protein shake ensures you are getting all the amino acids your body needs.

When looking for a good pre gastric bypass diet protein shake, make sure to check the label for a complete amino acid profile. It should include all nine essential amino acids, as well as some of the non-essential ones. This will guarantee that you’re getting a full spectrum of nutrition in each shake - giving your body the fuel it needs to ease through your procedure.

A protein that is hydrolyzed 

Hydrolyzed protein is a form of protein that has undergone hydrolysis, a process by which large (and difficult to digest) protein molecules are broken down into smaller pieces called “peptides.” Hydrolyzed protein is much easier for the body to digest and absorb than normal protein. 

This means it will help avoid an upset stomach, and will also allow you to get more nutrients (and benefits) from your protein supplement. 

A protein that is sugar free

You should limit sugar before your surgery as part of your pre gastric bypass diet, as this can help to reduce the size of your liver, which is crucial for successful surgery. This means checking your protein shakes for any traces of added sugar.

It’s also incredibly important to avoid sugar-filled supplements after your surgery too, as you can experience dumping syndrome. 

Dumping syndrome is a condition that can occur after having surgery to remove all or part of your stomach. It can happen when food moves too quickly from the stomach to the small intestine, and particularly affects foods that are high in sugar.

Symptoms of dumping syndrome include nausea, vomiting, belly pain and cramping, diarrhea, feeling faint or passing out, and sweating. Please speak with your doctor immediately if you experience those symptoms following your procedure. 

As long as you get adequate protein, and follow the pre bariatric diet carefully, your gastric bypass should go smoothly! 

Follow the steps for bariatric success

The pre gastric bypass diet may not be the most fun, but it is critical for your health and the success of your surgery. You’re making a monumental change to your life and greatly improving your overall health, so sacrificing your diet for a few weeks is absolutely worth it! 

Remember - this diet won’t last forever, but the positive effects of your procedure can! Just stick with your diet, follow your doctor’s directions, and before you know it, you’ll be enjoying your favorite foods again. 

In the meantime, a high-quality, hydrolyzed collagen protein can help get you through your pre and post gastric bypass diet. 

Medical-grade collagen supplements like the ones from ProT Gold contain added tryptophan that makes them a complete protein, and come in both powder and liquid forms, so you can customize your diet as you see fit.