Gastric bypass decreases your stomach size and changes the way your body digests food. After surgery, you’ll likely need to make dietary changes to help your body heal and to get the nutrients you need.

Gastric bypass surgery is a type of weight loss surgery that involves decreasing the size of your stomach. As a result of this surgery, you may feel full after eating smaller amounts of food.

During this procedure, a surgeon also connects your new, smaller stomach pouch directly to your small intestine. Food you eat will bypass most of your stomach and the upper part of your small intestine. Because of this, your body will absorb fewer calories.

Before undergoing gastric bypass surgery, you must qualify for the surgery and understand the risks and benefits involved.

According to the American Society for Metabolic and Bariatric Surgery, you may be eligible for gastric bypass surgery if you:

  • have a body mass index (BMI) of 35 or greater
  • have a BMI of 30 or greater and type 2 diabetes
  • have a BMI of 30–34.9 and haven’t been able to lose weight with medication or lifestyle changes

To be a viable candidate, you should also be ready to learn new dietary habits that can help ensure that the surgery has positive and lifelong effects.

Before your surgery, you’ll need to make plans to follow a special diet both before and after the procedure.

The pre-surgery diet is geared toward reducing the amount of fat in and around your liver. This reduces the risk of complications during the procedure.

After the surgery, your doctor will tailor the general diet guidelines for you. The postsurgery diet usually consists of several weekly phases. It helps you recover, meet the needs of your now-smaller stomach, and gain healthier eating habits.

Losing weight before surgery helps reduce the amount of fat in and around your liver and abdomen. This may allow you to have a laparoscopy rather than open surgery. Laparoscopic surgery is less invasive, requires much less recovery time, and is easier on your body.

Losing weight before your surgery not only helps keep you safer during the procedure but also helps you learn a new way of eating.

Your exact eating plan and pre-op weight loss goal will be determined by a healthcare professional, likely with the help of a registered dietitian.

Your eating plan may begin as soon as you’re cleared for the procedure. If you don’t lose enough weight before surgery, the procedure may be postponed or canceled. For this reason, you should start the diet plan as soon as you can.


Guidelines will vary from person to person, but they may include the following:

What to eat

The pre-op diet largely consists of protein shakes and other high protein, low calorie foods that are easy to digest.

Protein helps bolster and protect muscle tissue. This can help your body burn fat instead of muscle for fuel. Protein also helps keep your body strong, which can speed up recovery.

As your surgery date nears, you may need to follow a mostly liquid or liquid-only diet. Depending on your weight and your overall health, your doctor may allow you to eat some solids during this time. These might include fish, watered-down hot cereal, or soft-boiled eggs.

Ahead of your surgery, make sure you ask the anesthesiologist for instructions about what you can or can’t consume before surgery. The recommendations may vary depending on your situation. For example, your doctor may want you to drink carbohydrate-rich fluids up to 2 hours before surgery.

The postsurgery diet plan consists of several stages. Your bariatric surgery team or dietitian will determine how long each stage lasts and what you can eat and drink.

All stages stress the importance of watching your portion sizes. This habit will help you continue to lose weight and prepare you for how you’ll eat for the rest of your life.

Stage 1: Liquid diet

During stage 1, your nutritional intake is geared toward helping your body heal from surgery. Your diet can help you avoid postoperative complications.

For the first few days, you’re only allowed to drink a few ounces of clear liquids at a time. This helps your stomach heal without being stretched out by food.

After clear liquids, you’ll graduate to additional types of liquid, which may include:

  • decaffeinated coffee and tea
  • skim milk
  • thin soup and broth
  • unsweetened juice
  • sugar-free gelatin
  • sugar-free ice pops

Stage 2: Pureed diet

Once your doctor decides you’re ready, you can move on to stage 2. This stage consists of pureed foods that have a thick, pudding-like consistency.

You can puree many foods at home with a food processor, blender, or other device.

Spicy seasonings may irritate your stomach, so you may need to avoid these completely or try them one at a time. Avoid fruits and vegetables that have lots of seeds, such as strawberries or kiwi. You may also need to stay away from foods that are too fibrous to liquefy, such as broccoli and cauliflower.

Instead, choose foods that liquefy well, such as:

Stage 1 foods (which don’t contain solids) and vegetable juices such as V8 are also convenient options.

However, at this stage, it’s important not to drink fluids with your meals.

Stage 3: Soft-foods diet

You’ll probably eat nothing but pureed food for several weeks. Once your doctor decides you’re ready, you can start adding soft, easy-to-chew foods into your diet. These may include:

  • soft-boiled eggs
  • cottage cheese
  • ground lean meat or poultry
  • baked or steamed white fish
  • fresh fruit without skin, or canned fruits such as peaches and pears
  • cooked, diced vegetables

It’s important to eat small bites. Eat a little at a time and be mindful of portion sizes.

Stage 4: Stabilization

Stage 4 of the gastric bypass diet involves reintroducing solid food. It typically starts about 2 months after surgery.

Because your stomach is much smaller, you’ll still need to dice or chop your food into small bites. Large pieces of food may cause a blockage, which can lead to pain, nausea, and vomiting.

Introduce new foods slowly. That way, you can best determine which ones your stomach can tolerate and which ones to avoid. Stop eating any food that causes abdominal discomfort, nausea, or vomiting.

Foods and drinks to avoid in stage 4

You should not yet try to eat certain foods and drinks, such as those that are hard to digest. These include:

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

About 4 months after surgery, you may be able to resume eating normally.

However, being mindful of your portion sizes is still important. Make sure your diet consists mostly of fruits, vegetables, lean protein, and healthy carbohydrates. Limit or avoid foods that are high in fat, carbohydrates, and calories.

Gastric bypass surgery changes the size of your stomach and the way you digest food. You’ll likely need to change some of your dietary habits in order to get the nutrients you need, meet your weight loss goals, and help prevent complications from surgery.

The guidelines for your postoperative diet will also serve you throughout life. They include:

  • Eat and drink slowly: Eating or drinking too quickly can cause food or liquid to move too rapidly from your stomach to your small intestine. This can cause symptoms such as nausea, vomiting, and cramping. Take at least 20–30 minutes to finish a meal.
  • Chew carefully: Eat only small pieces of food at a time and chew each piece thoroughly. This can help prevent larger pieces of food from getting stuck in the opening between your smaller stomach pouch and your small intestine.
  • Stay hydrated: Healthcare professionals recommend drinking around 64 ounces of fluids per day to avoid dehydration. Drinking with your meals can cause you to feel full and prevent you from eating enough nutrient-rich foods, so enjoy beverages between meals but not during meals.
  • Get enough protein: Your body needs protein to build muscle and stay strong. Many bariatric surgery programs will recommend getting 60–100 grams of protein per day. Focus on eating high protein foods and limiting high fat, high sugar ones.
  • Manage portion sizes: Ask your healthcare team or a dietitian for recommended portion sizes for the foods you eat. Using smaller plates and utensils is one way to help limit your portions.
  • Listen to your body: If you find that you can’t tolerate a certain food, such as something spicy or fried, don’t eat it.
  • Take recommended supplements: After gastric bypass, your body may have trouble absorbing vitamins and minerals. Your doctor may prescribe supplements such as vitamin B12, calcium, iron, and a multivitamin. You will likely need to take these for the rest of your life.

You may feel motivated to start or resume an exercise program. But right after surgery, you need to let your body heal. Go slowly.

Low impact exercises such as walking and swimming are good options for the first month. You may also benefit from simple yoga poses, stretching, and deep breathing exercises.

Over the next several months, you can slowly build up to strength training and cardio workouts.

Think in terms of movement as well as exercise. Simple lifestyle changes such as these can help boost your physical fitness:

  • walking instead of riding the bus
  • parking farther away from your destination
  • taking the stairs instead of the elevator

Following your recommended pre- and postsurgery dietary guidelines can help you avoid possible complications such as dehydration, nausea, and constipation.


Sometimes the connection between your stomach and your intestines can become narrowed. This can happen even if you’re careful about what you eat.

If you have nausea, vomiting, or stomach pain for more than 2 days, let your doctor know. These are all symptoms of a possible obstruction.

Dumping syndrome

Dumping syndrome happens when food moves too quickly from your stomach to your duodenum (the first part of your small intestine). It is common in people who have had gastric bypass surgery.

There are two types of dumping syndrome:

  • Early dumping syndrome causes symptoms 30 minutes after you eat.
  • Late dumping syndrome causes symptoms 1–3 hours after you eat.

Symptoms of early dumping syndrome include:

  • nausea
  • vomiting
  • diarrhea
  • bloating
  • an uncomfortably full feeling
  • stomach pain or cramping
  • sweating
  • lightheadedness
  • headache
  • flushing of your face
  • fast heartbeat

Symptoms of late dumping syndrome include:

  • lightheadedness
  • fainting
  • shakiness
  • tiredness
  • sweating
  • weakness
  • fast heartbeat

To help avoid dumping syndrome, a good general rule is to take at least 30 minutes to eat each meal. Limiting your portion sizes, eating and drinking slowly, and limiting your intake of high sugar, high fat foods can also help.

Eating and drinking at the same time may also cause dumping syndrome. This is because it increases the volume of your intake. Wait 30–45 minutes after eating before you drink any liquids, and always sip liquids very slowly.

Gastric bypass surgery can give you a new start toward health and fitness.

Following the recommended pre- and post-op diet will go a long way toward your success. It can also help protect you from surgical complications and teach you how to eat and drink well for the rest of your life.