Gastric Bypass Surgery: Overview

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Gastric bypass surgery is a type of bariatric or weight-loss surgery. Also known as Roux-en-Y gastric bypass, this procedure limits the amount of food you can eat and the number of calories you can absorb. It is one of the most common weight loss procedures in the United States.

This procedure can help people with obesity lose weight. But as with all major surgeries, gastric bypass carries some risks and requires careful preparation.

This article explains how gastric bypass surgery works, its benefits, and potential risks. It also details the lifestyle changes your healthcare provider will likely recommend to maintain results and avoid potential health complications.

A patient undergoing gastric bypass weight loss surgery
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What Is Gastric Bypass Surgery?

Gastric bypass surgery is performed by a bariatric surgeon in a hospital or surgical center under general anesthesia. This scheduled surgery requires a two- to five-day hospital stay and is performed in adults and, occasionally, adolescents.

The surgeon creates a small pouch (about the size of an egg) out of the patient's existing stomach. With a much smaller stomach, patients cannot eat as much food. The surgeon then connects the new stomach pouch to a lower part of the small intestine. By bypassing the upper part, fewer calories and nutrients are absorbed from any ingested food.

Surgical Techniques

In the majority of cases, gastric bypass is performed laparoscopically. This means that the surgeon uses long instruments to operate through tiny incisions.

Less commonly, the surgery is performed as open surgery. This means that the surgeon accesses the stomach and small intestine through a large incision in the abdomen.

The "Gold Standard"

According to the American Society for Metabolic and Bariatric Surgery, gastric bypass is considered the "gold standard" of weight-loss surgery. While a complex operation, when compared to adjustable gastric banding, sleeve gastrectomy, and similar procedures—gastric bypass is associated with greater and more sustained weight loss.

Criteria and Contraindications

While there are multiple benefits associated with gastric bypass surgery, not everyone is a candidate. The indications for undergoing gastric bypass include:

An exception to the above criteria is that Asian patients who have uncontrolled type 2 diabetes and a BMI as low as 27.5 may be considered for weight loss surgery.

BMI is a dated, flawed measure. It does not take into account factors such as body composition, ethnicity, sex, race, and age. 
Even though it is a biased measure, BMI is still widely used in the medical community because it’s an inexpensive and quick way to analyze a person’s potential health status and outcomes.

This exception stems from the fact that, when compared to whites, people of Asian origin are more likely to accumulate fat in their abdomen, as opposed to their buttocks, hips, and thighs. This abdominal fat buildup increases their risk for insulin resistance and heart disease, even at relatively low body mass index levels.

Contraindications to undergoing gastric bypass surgery include:

Potential Risks

Besides the risks that go along with any surgery—such as blood clots, pneumonia, or bleeding—some of the specific risks associated with gastric bypass surgery include:

  • Dumping syndrome: Dumping syndrome is a condition in which food moves very quickly from the stomach into the small intestine. It may cause feelings of nausea, cold sweats, light-headedness, and (often) severe diarrhea.
  • Malnutrition: Various protein and vitamin/mineral deficiencies may occur since this surgery changes the body's ability to absorb nutrients.
  • Leakage: A gastrointestinal leak of digestive juices and partially digested food may occur either where the small intestine is connected to the stomach or where it is connected to its own lower end.
  • Small bowel obstruction: An obstruction of the small bowel is most commonly caused by an internal hernia, which is when the bowel protrudes through a defect created surgically within the abdominal cavity.
  • Marginal ulcer formation: A marginal ulcer resembles a peptic ulcer. It is located near the site where the stomach pouch and small intestine connect.
  • Gastrogastric fistula: This complication refers to an abnormal tract that forms between the new stomach pouch and the old stomach remnant.
  • Anastomotic stenosis: Sometimes the connection between the stomach pouch and the small intestine (called the anastomosis) narrows, which can eventually lead to an inability to swallow liquids.

Purpose of Gastric Bypass Surgery

Weight loss is the primary purpose of gastric bypass surgery. With this comes the potential benefit of reversing or improving various obesity-related health conditions, such as:

Other possible benefits of gastric bypass include improved health-related quality of life and a reduction in all-cause mortality (death).

While the benefits of gastric bypass are vast, the operation is only the first step. Patients must be able to commit to various lifestyle changes after surgery in order to sustain their weight loss.

Therefore, even if a person meets the above-mentioned medical criteria for surgery, they still need to undergo several pre-surgical assessments in order to ensure they are medically, psychologically, and cognitively ready for this lifelong commitment.

To start, a thorough medical history and physical examination by a bariatric physician is required to be cleared for gastric bypass surgery. Several tests are often ordered to screen for or monitor the severity of a particular disease.

Some of these tests may include:

Based on test results and/or a patient's medical history, specialty consultations may be required. For example, an endocrinology consultation may be recommended for patients with type 2 diabetes and poorly controlled glucose levels.

Psychological and cognitive assessments are also required.

Goals of these psychological/cognitive assessments include:

  • Analyzing behaviors that may enhance or impair a patient's ability to sustain weight loss after surgery
  • Evaluating for potential substance abuse and eating disorders, such as binge eating disorder or night eating syndrome
  • Accessing motivation and executive functioning skills, such as planning and organizing, which are important for adhering to post-operative dietary and exercise recommendations

Final tests required for surgery clearance include:

  • An anesthesia preoperative evaluation
  • A nutritional assessment
  • Pregnancy counseling for women in their childbearing years
  • Cancer screenings (based on age) coordinated through the patient's primary care provider

Important Note

Surgeons and insurance companies have different requirements about whether a patient needs to make certain weight loss attempts in order to be approved for bariatric surgery. If you are considering gastric bypass surgery, be sure to discuss and clarify all requirements with your surgeon and insurance company. 

How to Prepare

Once you are cleared for surgery and your procedure date is scheduled, your surgical team will give you instructions on how to prepare.

These instructions may include:

  • Stopping smoking several months prior to surgery
  • Meeting with a bariatric registered dietitian weeks or months before surgery to learn about food preparation and what your post-surgical diet plan will look like
  • Consuming a low-calorie diet for about two weeks prior to surgery (to reduce liver volume, which can help the surgeon during the operation)
  • Stopping certain medications for a period of time before surgery (for example, non-steroidal anti-inflammatory medications, or NSAIDs)
  • Refraining from eating or drinking anything after midnight on the eve of your surgery
  • Packing personal items (e.g., toothbrush) for your hospital stay

What to Expect on the Day of Surgery

Once you are admitted and prepped for surgery, an antibiotic will be given and your anesthesia will be administered via an IV. Your surgeon will then perform the following steps:

  • Multiple incisions will be made in the upper abdomen through which various surgical instruments will be inserted (if performed laparoscopically).
  • Using these instruments, the surgeon will create a 30-mL pouch from the area of the stomach closest to the esophagus. The pouch will be completely detached from the rest of the stomach, and the remaining stomach will be stapled closed.
  • Once the pouch is formed, an incision will be made in the small intestine, dividing it into an upper and lower section.
  • The upper part of the small intestine (duodenum) will be bypassed, while the lower part (jejunum) will be pulled up and connected to the newly formed pouch.
  • The end of the bypassed duodenum will then be re-connected to the jejunum to allow food and digestive enzymes to mix.
  • The incisions will then be closed with dissolvable sutures or surgical staples.
  • Anesthesia will be stopped and you will be taken to a recovery room.


While recovering in the hospital after gastric bypass surgery, your surgical team will monitor your vital signs carefully and help control common post-surgical symptoms like pain, nausea, and vomiting.

On the morning of the second day after your surgery, you will begin sipping small, but frequent amounts of clear liquids. If you are tolerating clear liquids, you might be able to advance to full liquids (including protein shakes) by lunchtime.

You will engage in some form of physical activity (usually leg exercises) with the assistance of your nurse. Soon thereafter, you will begin getting out of bed and walking around. If you are experiencing any difficulties performing these exercises (perhaps due to post-surgical weakness or obesity-related mobility problems), your nurse or surgeon may call a physical therapist to assist you.

Upon discharge, your surgeon will give you specific instructions about recovering at home. You will likely be asked to:

  • Keep the incision site(s) clean and dry.
  • Avoid strenuous activities for three to six weeks after surgery.
  • Avoid heavy lifting for three months after surgery.
  • Gradually increase your activity every day (by six weeks, you should be walking two miles or more a day).
  • Maintain a full liquid diet that can slowly be advanced (under the guidance of your dietitian) to pureed and soft foods. By about six weeks, based on your individual tolerance, you will be able to eat solid foods.
  • Take daily nutritional supplements (complex multivitamin, calcium, vitamin D, iron, vitamin C, and vitamin B12).

When to Seek Medical Attention

As you recover from surgery, it's important to reach out to your surgeon if you develop any of the following symptoms:

  • Fever
  • Signs of a wound infection (e.g., redness, swelling, increased pain, or abnormal drainage)
  • Chest pain or trouble breathing
  • Nausea or vomiting that lasts more than 12 hours
  • Leg or calf pain, redness, or swelling
  • Urinating fewer than four times in 24 hours
  • Pain that is not eased with medication

Long-Term Care

After laparoscopic gastric bypass surgery, 80% of patients lose more than 70% of their excess body weight over two years, and 70% achieve greater than 50% over three years.

The key to maintaining this weight loss in the long-term includes the following practices:

  • Eating three (or six smaller) nutrient-packed meals each day—an example breakfast may consist of one egg, one half a cup of oatmeal, one half a cup of unsweetened applesauce, and one tablespoon of avocado.
  • Incorporating protein into every meal to meet daily requirements, which is around 60 grams. Consumption of a protein shake or a low-calorie protein food in between meals is often required.
  • Eating protein first, starch last, and using fats as a flavoring or to keep food moist
  • Eating slow, chewing foods thoroughly, and stopping eating when full
  • Avoiding all foods high in sugar or fat
  • Ensuring proper hydration between meals (around two liters of water a day)
  • Exercising regularly (30 minutes, five to seven days a week)

It will also be important to attend all of your follow-up appointments with your surgeon and bariatric dietitian. The purpose of these various appointments is to:

  • Evaluate for and manage potential complications or symptoms related to surgery (e.g., dumping syndrome, vomiting, and fatigue)
  • Monitor health conditions that now may be reversed or improved (e.g., type 2 diabetes)
  • Keep track of your weight loss progress
  • Identify any emotional or psychological needs after the surgery

For your long-term recovery, your surgeon may recommend that you join a bariatric surgery support group. Doing so may provide you with valuable resources and emotional guidance for issues like remaining committed to your lifestyle changes, dealing with any post-surgical body image concerns, and returning to work or dating life.

A Word From Verywell

Undergoing gastric bypass surgery is a lifelong decision. If you or a loved one is considering gastric bypass, or any weight-loss surgery, learn as much as you can about it and keep asking questions of your healthcare provider until you are confident that the decision you are making is the right one. Seek opinions from trusted and well-qualified medical professionals.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Jennifer Whitlock, RN, MSN, FN
Jennifer Whitlock, RN, MSN, FNP-C, is a board-certified family nurse practitioner. She has experience in primary care and hospital medicine.