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Bariatric Surgery

Definition & Facts

What is obesity?

Obesity is defined as having a body mass index (BMI) of 30 or more. BMI is a measure of your weight in relation to your height. Class 1 obesity means a BMI of 30 to 35, Class 2 obesity is a BMI of 35 to 40, and Class 3 obesity is a BMI of 40 or more. Classes 2 and 3, also known as severe obesity, are often hard to treat with diet and exercise alone.

Calculate your BMI to learn your BMI category.

What is bariatric surgery?

Bariatric surgery is an operation that helps you lose weight by making changes to your digestive system. Some types of bariatric surgeries make your stomach smaller, allowing you to eat and drink less at one time and making you feel full sooner. Other bariatric surgeries also change your small intestine—the part of your body that absorbs calories and nutrients from foods and beverages.

Bariatric surgery may be an option if you have severe obesity and have not been able to lose weight or keep from gaining back any weight you lost using other methods such as lifestyle treatment or medications. Bariatric surgery also may be an option if you have serious health problems, such as type 2 diabetes or sleep apnea, related to obesity. Bariatric surgery can improve many of the medical conditions linked to obesity, especially type 2 diabetes.

Does bariatric surgery always work?

Studies show that many people who have bariatric surgery lose about 15 to 30 percent of their starting weight on average, depending on the type of surgery they have. However, no method, including surgery, is sure to produce and maintain weight loss. Some people who have bariatric surgery may not lose as much as they hoped. Over time, some people regain a portion of the weight they lost. The amount of weight people regain may vary. Factors that affect weight regain may include a person’s level of obesity and the type of surgery he or she had.

Bariatric surgery does not replace healthy habits, but may make it easier for you to consume fewer calories and be more physically active. Choosing healthy foods and beverages before and after the surgery may help you lose more weight and keep it off long term. Regular physical activity after surgery also helps keep the weight off. To improve your health, you must commit to a lifetime of healthy lifestyle habits and following the advice of your health care providers.

Three ladies exercising
Maintaining healthy lifestyle habits may help
you succeed after bariatric surgery.

How much does bariatric surgery cost?

On average, bariatric surgery costs between $15,000 and $25,000, depending on what type of surgery you have and whether you have surgery-related problems. Costs may be higher or lower based on where you live. The amount your medical insurance will pay varies by state and insurance provider.

Medicare and some Medicaid programs cover three common types of bariatric surgery—gastric bypass, gastric band, and gastric sleeve surgery—if you meet certain criteria and have a doctor’s recommendation. Some insurance plans may require you to use approved surgeons and facilities. Some insurers also require you to show that you were unable to lose weight by completing a nonsurgical weight-loss program or that you meet other requirements.

Your health insurance company or your regional Medicare or Medicaid office will have more information about bariatric surgery coverage, options, and requirements.

Types of Bariatric Surgery

The type of surgery that may be best to help a person lose weight depends on a number of factors. You should discuss with your doctor what kind of surgery might be best for you or your teen.

What is the difference between open and laparoscopic surgery?

In open bariatric surgery, surgeons make a single, large cut in the abdomen. More often, surgeons now use laparoscopic surgery, in which they make several small cuts and insert thin surgical tools through the cuts. Surgeons also insert a small scope attached to a camera that projects images onto a video monitor. Laparoscopic surgery has fewer risks than open surgery and may cause less pain and scarring than open surgery. Laparoscopic surgery also may lead to a faster recovery.

Open surgery may be a better option for certain people. If you have a high level of obesity, have had stomach surgery before, or have other complex medical problems, you may need open surgery.

What are the surgical options?

In the United States, surgeons use three types of operations most often:

  • laparoscopic adjustable gastric band
  • gastric sleeve surgery, also called sleeve gastrectomy
  • gastric bypass

Surgeons use a fourth operation, biliopancreatic diversion with duodenal switch, less often.

Laparoscopic Adjustable Gastric Band

In this type of surgery, the surgeon places a ring with an inner inflatable band around the top of your stomach to create a small pouch. This makes you feel full after eating a small amount of food. The band has a circular balloon inside that is filled with salt solution. The surgeon can adjust the size of the opening from the pouch to the rest of your stomach by injecting or removing the solution through a small device called a port placed under your skin.

After surgery, you will need several follow-up visits to adjust the size of the band opening. If the band causes problems or is not helping you lose enough weight, the surgeon may remove it.

The U.S. Food and Drug Administration (FDA) has approved use of the gastric band for people with a BMI of 30 or more who also have at least one health problem linked to obesity, such as heart disease or diabetes.

Gastric Sleeve

In gastric sleeve surgery, also called vertical sleeve gastrectomy, a surgeon removes most of your stomach, leaving only a banana-shaped section that is closed with staples. Like gastric band surgery, this surgery reduces the amount of food that can fit in your stomach, making you feel full sooner. Taking out part of your stomach may also affect gut hormones or other factors such as gut bacteria that may affect appetite and metabolism. This type of surgery cannot be reversed because some of the stomach is permanently removed.

Gastric Bypass

Gastric bypass surgery, also called Roux-en-Y gastric bypass, has two parts. First, the surgeon staples your stomach, creating a small pouch in the upper section. The staples make your stomach much smaller, so you eat less and feel full sooner.

Next, the surgeon cuts your small intestine and attaches the lower part of it directly to the small stomach pouch. Food then bypasses most of the stomach and the upper part of your small intestine so your body absorbs fewer calories. The surgeon connects the bypassed section farther down to the lower part of the small intestine. This bypassed section is still attached to the main part of your stomach, so digestive juices can move from your stomach and the first part of your small intestine into the lower part of your small intestine. The bypass also changes gut hormones, gut bacteria, and other factors that may affect appetite and metabolism. Gastric bypass is difficult to reverse, although a surgeon may do it if medically necessary.

Duodenal Switch

This surgery, also called biliopancreatic diversion with duodenal switch, is more complex than the others. The duodenal switch involves two separate surgeries. The first is similar to gastric sleeve surgery. The second surgery redirects food to bypass most of your small intestine. The surgeon also reattaches the bypassed section to the last part of the small intestine, allowing digestive juices to mix with food.

This type of surgery allows you to lose more weight than the other three. However, this surgery is also the most likely to cause surgery-related problems and a shortage of vitamins, minerals, and protein in your body. For these reasons, surgeons do not perform this surgery as often.

Most Common Weight-loss Surgeries

Gastric Band

Illustration of Gastric Band

What it is

Surgeon places an inflatable band around top part of stomach, creating a small pouch with an adjustable opening.


  • Can be adjusted and reversed.
  • Short hospital stay and low risk of surgery-related problems.
  • No changes to intestines.
  • Lowest chance of vitamin shortage.


  • Less weight loss than other types of bariatric surgery.
  • Frequent follow-up visits to adjust band; some people may not adapt to band.
  • Possible future surgery to remove or replace a part or all of the band system.

Gastric Sleeve

Illustration of Gastric Sleeve

What it is

Surgeon removes about 80 percent of stomach, creating a long, banana-shaped pouch.


  • Greater weight loss than gastric band.
  • No changes to intestines.
  • No objects placed in body.
  • Short hospital stay.


  • Cannot be reversed.
  • Chance of vitamin shortage.
  • Higher chance of surgery-related problems than gastric band.
  • Chance of acid reflux.

Gastric Bypass

Illustration of Gastric Bypass

What it is

Surgeon staples top part of stomach, creating a small pouch and attaching it to middle part of small intestine.


  • Greater weight loss than gastric band.
  • No objects placed in body.


  • Difficult to reverse.
  • Higher chance of vitamin shortage than gastric band or gastric sleeve.
  • Higher chance of surgery-related problems than gastric band.
  • May increase risk of alcohol use disorder.

Adapted from: Bariatric surgery procedures. American Society for Metabolic and Bariatric Surgery (ASMBS) website. Accessed May 24, 2016.

Image credit: Walter Pories, M.D., FACS.

What should I expect before surgery?

Before surgery, you will meet with several health care providers, such as a dietitian, a psychiatrist or psychologist, an internist, and a bariatric surgeon.

  • The doctor will ask about your medical history, do a thorough physical exam, and order blood tests. If you are a smoker, he or she will likely ask you to stop smoking at least 6 weeks before your surgery.
  • The surgeon will tell you more about the surgery, including how to prepare for it and what type of follow-up you will need.
  • The dietitian will explain what and how much you will be able to eat and drink after surgery and help you to prepare for how your life will change after surgery.
  • The psychiatrist or psychologist may do an assessment to see if bariatric surgery is an option for you.

These health care providers also will advise you to become more active and adopt a healthy eating plan before and after surgery. In some cases, losing weight and bringing your blood sugar levels closer to normal before surgery may lower your chances of having surgery-related problems.

Some bariatric surgery programs have groups you can attend before and after surgery that can help answer questions about the surgery and offer support.

What should I expect after surgery?

After surgery, you will need to rest and recover. Although the type of follow-up varies by type of surgery, you will need to take supplements that your doctor prescribes to make sure you are getting enough vitamins and minerals.

Walking and moving around the house may help you recover more quickly. Start slowly and follow your doctor’s advice about the type of physical activity you can do safely. As you feel more comfortable, add more physical activity.

After surgery, most people move from a liquid diet to a soft diet such as cottage cheese, yogurt, or soup, and then to solid foods over several weeks. Your doctor, nurse, or dietitian will tell you which foods and beverages you may have and which ones you should avoid. You will need to eat small meals and chew your food well.

How much weight can I expect to lose?

The amount of weight people lose after bariatric surgery depends on the individual and on the type of surgery he or she had. A study following people for 3 years after surgery found that those who had gastric band surgery lost an average of about 45 pounds. People who had gastric bypass lost an average of 90 pounds.1 Most people regained some weight over time, but weight regain was usually small compared to their initial weight loss.

Researchers know less about the long-term results of gastric sleeve surgery, but the amount of weight loss seems to be similar to or slightly less than gastric bypass.

Your weight loss could be different. Remember, reaching your goal depends not just on the surgery but also on sticking with healthy lifestyle habits throughout your life.

Weight-loss Devices

The FDA has approved several new weight-loss devices that do not permanently change your stomach or small intestine. These devices cause less weight loss than bariatric surgery, and some are only temporary. The devices may have risks, so talk with your doctor if you’re thinking about any of these options. Researchers haven’t studied any of them over a long period of time and don’t know the long-term risks and benefits.

  • The electrical stimulation system uses a device implanted in your abdomen, by way of laparoscopic surgery, that blocks nerve activity between your stomach and brain. The device works on the vagus nerve, which helps signal the brain that the stomach feels full or empty.
  • The gastric balloon system consists of one or two balloons placed in your stomach through a tube inserted through your mouth. Your doctor or nurse will give you a sedative before the procedure. Once the balloons are in your stomach, doctors inflate them with salt water so they take up space in your stomach and help you feel fuller. You will need to have the balloons removed after 6 months or a year.
  • A new device uses a pump to drain part of the food in your stomach after a meal. The device includes a tube that goes from the inside of your stomach to a port on the outside of your abdomen. The port is a small valve that fits over the opening in your abdomen. About 20 to 30 minutes after eating, you attach tubing from the port to the pump and open the valve. The pump drains your stomach contents through a tube into the toilet, so that your body doesn’t absorb about 30 percent of calories you ate. You can have the device removed at any time.

1 Inge TH, Courcoulas AP, Jenkins TM, et al. Weight loss and health status 3 years after bariatric surgery in adolescents. The New England Journal of Medicine. 2016;374(2):113–123.

Bariatric Surgery Benefits

What are the benefits of bariatric surgery?

Bariatric surgery can help you lose weight and improve many health problems related to obesity. These health problems include

You may be better able to move around and be physically active after surgery. You might also notice your mood improve and feel like your quality of life is better.

Man playing soccer with his young son.
You may be better able to move around and be physically active after surgery.

Bariatric Surgery Side Effects

What are the side effects of bariatric surgery?

Side effects may include

  • bleeding
  • infection
  • leaking from the site where the sections of the stomach or small intestine, or both, are stapled or sewn together
  • diarrhea
  • blood clots in the legs that can move to the lungs and heart

Rarely, surgery-related problems can lead to death.

Other side effects may occur later. Your body may not absorb nutrients well, especially if you don’t take your prescribed vitamins and minerals. Not getting enough nutrients can cause health problems, such as anemia and osteoporosis. Gallstones can occur after rapid weight loss. Some doctors prescribe medicine for about 6 months after surgery to help prevent gallstones. Gastric bands can erode into the stomach wall and need to be removed.

Vitamins and nutrients in pill format sitting in a person’s hand.
Taking your prescribed vitamins and minerals will help you get enough nutrients.

Other problems that could occur later include strictures and hernias. Strictures—narrowing of the new stomach or connection between the stomach and small intestine—make it hard to eat solid food and can cause nausea, vomiting, and trouble swallowing. Doctors treat strictures with special instruments to expand the narrowing. Two kinds of hernias may occur after bariatric surgery—at the incision site or in the abdomen. Doctors repair hernias with surgery.

Some research suggests that bariatric surgery, especially gastric bypass, may change the way your body absorbs and breaks down alcohol, and may lead to more alcohol-related problems after surgery.

Potential Candidates for Bariatric Surgery

Who is a good adult candidate for bariatric surgery?

Bariatric surgery may be an option for adults who have

  • a body mass index (BMI) of 40 or more, OR
  • a BMI of 35 or more with a serious health problem linked to obesity, such as type 2 diabetes, heart disease, or sleep apnea
  • a BMI of 30 or more with a serious health problem linked to obesity, for the gastric band only

Having surgery to lose weight is a serious decision. If you are thinking about having bariatric surgery, you should know what’s involved. Your answers to the following questions may help you decide if surgery is an option for you:

  • Have you been unable to lose weight or keep it off using nonsurgical methods such as lifestyle changes or drug treatment?
  • Do you understand what the operation involves and its risks and benefits?
  • Do you understand how your eating and physical activity patterns will need to change after you have surgery?
  • Can you commit to following lifelong healthy eating and physical activity habits, medical follow-up, and the need to take extra vitamins and minerals?

Who is a good teen candidate for bariatric surgery?

Doctors sometimes use bariatric surgery to treat teens with severe obesity who also have obesity-related health problems. Bariatric surgery often improves health problems that could grow worse in adulthood if the teen remains obese.

Surgery may be an option for teens who have gone through puberty and reached their adult height, and have

  • a BMI of 35 or more with serious obesity-related health problems, such as type 2 diabetes or severe sleep apnea, OR
  • a BMI of 40 or more with less severe health problems, such as high blood pressure or high cholesterol2
A photo of a woman smiling
Bariatric surgery may be an option for teens who have a BMI of 35 or more.

Studies suggest that bariatric surgery is fairly safe for teens and can improve health problems such as type 2 diabetes for at least 3 years after surgery. Teens who took part in a study that followed them for 3 years after surgery lost an average of 90 pounds and kept most of the weight off.3 They also reported improved quality of life related to their weight. Researchers continue to study the long-term effects, which currently are unknown.

Like adults, teens who are thinking about weight-loss surgery should be prepared for the lifestyle changes they will need to make after the surgery. A surgical center that focuses on the unique needs of youth may help the teen patient prepare for and adjust to these changes. Parents and caregivers also should be prepared and ready to support their child.


Clinical Trials

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and other components of the National Institutes of Health (NIH) conduct and support research into many diseases and conditions.

What are clinical trials and are they right for you?

Clinical trials are part of clinical research and at the heart of all medical advances. Clinical trials look at new ways to prevent, detect, or treat disease in people of all ages. Researchers also use clinical trials to look at other aspects of care, such as improving the quality of life for people with chronic illnesses. Find out more about clinical trials.

Watch a video of NIDDK Director Dr. Griffin P. Rodgers explaining the importance of participating in clinical trials.

What clinical trials are open?

Clinical trials that are currently open and are recruiting can be viewed at

What is the Longitudinal Assessment of Bariatric Surgery?

From 2003 to 2016, the NIDDK partnered with researchers to create the Longitudinal Assessment of Bariatric Surgery, or LABS. The researchers examined the safety and effectiveness of weight-loss surgery in adults. A separate group of researchers are doing similar research with teens, called Teen-LABS.

LABS found that weight-loss surgery performed by experienced surgeons is relatively safe, leads to large weight loss, and improves many weight-related health problems. Three years after surgery, about half of adult gastric bypass patients had lost at least 90 pounds, or almost one-third of their starting weight. Half of gastric band patients had lost at least 44 pounds, or 16 percent of their starting weight.4

Teens who had gastric bypass or gastric sleeve surgery had similar results. Three years after surgery, teens lost an average of 27 percent of their starting weight, with improved overall health and quality of life.5


This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.