Bariatric Surgery 

for Severe Obesity

U.S. Department of Health 

and Human Services

NATIONAL INSTITUTES OF HEALTH

WIN Weight-control Information Network

Severe obesity is a chronic condition that is hard to treat with diet and 

exercise alone. Bariatric surgery is an operation on the stomach and/or 

intestines that helps patients with extreme obesity to lose weight. This 

surgery is an option for people who cannot lose weight by other means 

or who suffer from serious health problems related to obesity. The 

surgery restricts food intake, which promotes weight loss and reduces 

the risk of type 2 diabetes. Some surgeries also interrupt how food is 

digested, preventing some calories and nutrients, such as vitamins, 

from being absorbed. Recent studies suggest that bariatric surgery may 

even lower death rates for patients with severe obesity. The best results 

occur when patients follow surgery with healthy eating patterns and 

regular exercise.

Bariatric Surgery for Adults

Currently, bariatric surgery may be an option for adults with severe 

obesity. Body mass index (BMI), a measure of height in relation to 

weight, is used to define levels of obesity. Clinically severe obesity 

is a BMI ≥ 40 or a BMI ≥ 35 with a serious health problem linked 

to obesity. Such health problems could be type 2 diabetes, heart 

disease, or severe sleep apnea (when breathing stops for short 

periods during sleep).

Recent Development

The Food and Drug Administration (FDA) has approved use of an 

adjustable gastric band (or AGB, see page 3) for patients with BMI ≥

30 who also have at least one condition linked to obesity, such as heart 

disease or diabetes.

Who is a good adult candidate for surgery?

Having surgery to produce weight loss is a serious decision. Anyone 

thinking about having this surgery should know what it involves. 

Answers to the following questions may help patients decide whether 

weight-loss surgery is right for them.

Bariatric surgery

may be the next

step for people who

remain severely

obese after trying

approaches other

than surgery,

especially if they

have a disease

linked to obesity.
2

Is the patient:

•	 Unlikely to lose weight or keep it off over 

the long term using other methods? 

•	 Well informed about the surgery and 

treatment effects? 

•	 Aware of the risks and benefits of surgery? 

•	 Ready to lose weight and improve his or 

her health? 

•	 Aware of how life may change after the 

surgery? (For example, patients need to 

adjust to side effects, such as the need to 

chew food well and the loss of ability to 

eat large meals.) 

•	 Aware of the limits on food choices, and 

occasional failures? 

•	 Committed to lifelong healthy eating and 

physical activity, medical follow-up, and the 

need to take extra vitamins and minerals?

There is no sure method, including surgery, to 

produce and maintain weight loss. Some patients 

who have bariatric surgery may have weight loss 

that does not meet their goals. Research also 

suggests that many patients regain some of the lost 

weight over time. The amount of weight regain 

may vary by extent of obesity and type of surgery. 

Habits such as snacking often on foods high in 

calories or not exercising can affect the amount of 

weight loss and weight regain. Problems that may 

occur with the surgery, like a stretched pouch or 

separated stitches, may also affect the amount of 

weight loss.

Success is possible. Patients must commit to 

changing habits and having medical follow-up for 

the rest of their lives.

Bariatric Surgery for Youth

Rates of obesity among youth are high. Bariatric 

surgery is sometimes used to treat youth with

1. Inge TH, Krebs NF, Garcia VF, et al. Bariatric surgery for severely 

overweight adolescents: concerns and recommendations. Pediatrics. 2004 

Jul;114(1):217-23.

2. Wilson ST, Thomas HI, Randall SB. Bariatric surgery in adolescents: 

recent national trends in use and in-hospital outcome. Archives of 

extreme obesity. Although it is becoming clear that 

teens can lose weight after bariatric surgery, many 

questions still exist about the long-term effects on 

teens’ developing bodies and minds.

Who is a good youth candidate for surgery?

Experts in childhood obesity and bariatric surgery 

suggest that families consider surgery only after youth 

have tried for at least 6 months to lose weight and 

have not had success.1

 Candidates should meet the 

following criteria:

•	 Have extreme obesity (BMI ≥ 40 )

•	 Be their adult height (usually at age 13 or 

older for girls and 15 or older for boys)

•	 Have serious health problems linked to weight, 

such as type 2 diabetes or sleep apnea, that 

may improve with bariatric surgery

In addition, health care providers should assess 

potential patients and their parents to see how 

emotionally prepared they are for the surgery and the 

lifestyle changes they will need to make. Health care 

providers should also refer young patients to special 

youth bariatric surgery centers that focus on meeting 

the unique needs of youth. 

Mounting evidence suggests that bariatric surgery 

can favorably change both the weight and health of 

youth with extreme obesity. Over the years, gastric 

bypass surgery (see page 4) has been the main 

operation used to treat extreme obesity in youth. 

An estimated 2,700 youth bariatric surgeries were 

performed between 1996 and 2003.2

 A review of 

short-term data from the largest inpatient database 

in the United States suggests that these surgeries 

are at least as safe for youth as adults. As yet, AGB 

has not been approved for use in the United States 

for people younger than age 18. However, favorable 

weight-loss outcomes after AGB for youth have 

been reported abroad. 

Pediatrics & Adolescent Medicine. 2007;161(3):217-221.
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The Normal Digestive Process

Normally, as food moves along the digestive 

tract, digestive juices and enzymes digest and 

absorb calories and nutrients. After we chew and 

swallow our food, it moves down the esophagus 

to the stomach, where a strong acid continues the 

digestive process. The stomach can hold about 

3 pints of food at one time. When the stomach 

contents move to the duodenum (the first part 

of the small intestine), bile and pancreatic juice 

speed up digestion. Most of the iron and calcium 

in the food we eat is absorbed there. The other 

two parts of the nearly 20 feet of small intestine 

absorb nearly all of the remaining calories and 

nutrients. The food particles that cannot be 

digested in the small intestine reside in the large 

intestine until eliminated.

How does surgery promote weight loss?

Bariatric surgery restricts food intake, which leads 

to weight loss. Patients who have bariatric surgery 

must commit to a lifetime of healthy eating and 

regular exercise. These healthy habits may help 

patients maintain weight loss after surgery.

Types of Bariatric Surgery

The type of surgery that may help an adult or youth 

depends on a number of factors. Patients should 

discuss with their health care providers what kind of 

surgery is suitable for them.

What is the difference between open and 

laparoscopic surgery?

Bariatric surgery may be performed through “open” 

approaches, which involve cutting the stomach 

in the standard manner, or by laparoscopy. With 

the latter approach, surgeons insert complex 

instruments through 1/2-inch cuts and guide a 

small camera that sends images to a monitor. Most 

bariatric surgery today is laparoscopic because it 

requires a smaller cut, creates less tissue damage, 

leads to earlier hospital discharges, and has fewer 

problems, especially hernias occurring after surgery. 

However, not all patients are suitable for 

laparoscopy. Patients who are considered extremely 

obese, who have had previous stomach surgery, or 

who have complex medical problems may require 

the open approach. Complex medical problems 

may include having severe heart and lung disease 

or weighing more than 350 pounds.

What are the surgical options?

There are four types of operations that are 

commonly offered in the United States: 

AGB, Roux-en-Y gastric bypass (RYGB), 

biliopancreatic diversion with a duodenal switch 

(BPD-DS), and vertical sleeve gastrectomy 

(VSG). (See Figure 1.) Each surgery has its own 

benefits and risks. The patient and provider 

should work together to select the best option 

by considering the benefits and risks of each 

type of surgery. Other factors to consider 

include the patient’s BMI, eating habits, health 

conditions related to obesity, and previous 

stomach surgeries.

Adjustable Gastric Band

AGB works mainly by decreasing food intake. 

Food intake is reduced by placing a small braceletlike band around the top of the stomach to restrict 

the size of the opening from the throat to the 

stomach. The surgeon can then control the size 

of the opening with a circular balloon inside the 

band. This balloon can be inflated or deflated with 

saline solution to meet the needs of the patient. 

Figure 1

Diagram of Surgical Options. Image credit: Walter Pories, M.D. FACS.
4

Roux-en-Y Gastric Bypass

RYGB restricts food intake. RYGB also decreases 

how food is absorbed. Food intake is limited by 

a small pouch that is similar in size to the pouch 

created with AGB (see page 3). Also, sending food 

directly from the pouch into the small intestine affects how the digestive tract absorbs food. The food

is absorbed differently because the stomach, duodenum, and upper intestine no longer have contact 

with food.

Biliopancreatic Diversion with a Duodenal Switch

BPD-DS, usually referred to as a “duodenal 

switch,” is a complex bariatric surgery that includes 

three features. One feature is to remove a large part 

of the stomach. This step makes patients feel full 

sooner when eating than they did before surgery. 

Feeling full sooner encourages patients to eat less. 

Another feature is re-routing food away from much 

of the small intestine to limit how the body absorbs 

food. The third feature changes how bile and other 

digestive juices affect the body’s ability to digest 

food and absorb calories. This step also helps lead 

to weight loss.

In removing a large part of the stomach, the 

surgeon creates a more tubular “gastric sleeve” 

(also known as a VSG, discussed later). The smaller 

stomach sleeve remains linked to a very short part 

of the duodenum, which is then directly linked to a 

lower part of the small intestine. This surgery leaves 

a small part of the duodenum available to absorb 

food and some vitamins and minerals.

However, when the patient eats food, it bypasses 

most of the duodenum. The distance between 

the stomach and colon becomes much shorter 

after this operation, thus limiting how food is 

absorbed. BPD-DS produces significant weight 

loss. However, a decrease in the amount of food, 

vitamins, and minerals absorbed creates chances 

for long-term problems.

Some of these problems are anemia (lower 

than normal count for red blood cells) or 

osteoporosis (loss of bone mass that can make 

bones brittle). 

Vertical Sleeve Gastrectomy 

VSG surgery restricts food intake and decreases 

the amount of food used. Most of the stomach is 

removed during this surgery, which may decrease 

ghrelin, a hormone that prompts appetite. Lower 

amounts of ghrelin may reduce hunger more than 

other purely restrictive surgeries, such as AGB.

VSG has been performed in the past mainly as 

the first stage of BPD-DS (discussed earlier) in 

patients who may be at high risk for problems

from more extensive types of surgery. These 

patients’ high risk levels are due to body weight 

or medical issues. However, more recent research 

indicates that some patients who have VSG can 

lose a lot of weight with VSG alone and avoid a 

second procedure. Researchers do not yet know 

how many patients who have VSG alone will need 

a second stage procedure. 

What are the side effects of these 

surgeries?

Some side effects may include bleeding, infection, 

leaks from the site where the intestines are sewn 

together, diarrhea, and blood clots in the legs that 

can move to the lungs and heart. 

Examples of side effects that may occur later 

include nutrients being poorly absorbed, especially 

in patients who do not take their prescribed 

vitamins and minerals. In some cases, if patients do 

not address this problem promptly, diseases may 

occur along with permanent damage to the nervous 

system. These diseases include pellagra (caused by 

lack of vitamin B3—niacin), beri beri (caused by 

lack of vitamin B1—thiamine) and kwashiorkor 

(caused by lack of protein). 
5

Other late problems include strictures (narrowing 

of the sites where the intestine is joined) and 

hernias (part of an organ bulging through a weak 

area of muscle). 

Two kinds of hernias may occur after a patient 

has bariatric surgery. An incisional hernia is a 

weakness that sticks out from the abdominal wall’s 

connective tissue and may cause a blockage in the 

bowel. An internal hernia occurs when the small 

bowel is displaced into pockets in the lining of the 

abdomen. These pockets occur when the intestines 

are sewn together. Internal hernias are thought to 

be more dangerous than incisional ones and need 

prompt attention to avoid serious problems.

Some patients may also require emotional 

support to help them through the changes in 

body image and personal relationships that occur 

after the surgery. 

Medical Costs

Bariatric procedures, on average, cost from $20,000 

to $25,000. Medical insurance coverage varies 

by state and insurance provider. In 2004, the 

U.S. Department of Health and Human Services 

reduced barriers to obtaining Medicare coverage for 

obesity treatments. Bariatric surgery may be covered 

under these conditions:

•	 If the patient has at least one health problem 

linked to obesity

•	 If the procedure is suitable for the patient’s 

medical condition

•	 If approved surgeons and facilities are involved 

Patients can contact staff at their regional 

Medicare, Medicaid, or health insurance office 

to find out if the procedure is covered and to 

obtain facts about options.

Research

In 2003, the National Institute of Diabetes and 

Digestive and Kidney Diseases (NIDDK) of the NIH 

partnered with researchers to create the Longitudinal 

Assessment of Bariatric Surgery, or LABS. LABS 

researchers are experts in bariatric surgery, obesity 

research, internal medicine, behavioral science, and 

related fields. Their mission is to plan and conduct 

studies that will lead to more knowledge about 

bariatric surgery and its impact on the health and 

well-being of patients with extreme obesity. More 

information about LABS is available at http://www.

niddklabs.org. 

To help determine if bariatric surgery is appropriate 

for youth, NIH launched Teen-LABS in 2007. 

From 2007 to 2012, the multicenter study is 

collecting data from teens who plan to have surgery. 

The data will help to evaluate bariatric surgery’s 

benefits and risks. Researchers are collecting data 

about medical problems related to obesity, other 

health risk factors, and quality of life from these 

patients before they have surgery and 2 years after 

surgery. Researchers will then compare the teen 

outcomes to data from adults. These websites offer 

more information about Teen-LABS: 

http://www.nih.gov/news/pr/apr2007/niddk-16.htm

and http://www.cincinnatichildrens.org/teen-LABS.

Resources

The following list of publications, websites, and 

organizations may be of use for patients or health 

care providers discussing bariatric surgery.

Additional Reading from the Weightcontrol Information Network

Active at Any Size. This fact sheet provides 

ideas and tips on how people considered to be 

overweight or obese can be physically active. It 

focuses on overcoming common barriers and setting 

goals. Available at http://www.win.niddk.nih.gov/

publications/active.htm.
6

Binge Eating Disorder. This fact sheet provides information and 

resources for patients who may have binge eating disorder. Available 

at http://www.win.niddk.nih.gov/publications/binge.htm.

Dieting and Gallstones. This fact sheet explains what gallstones are, 

how they form, and the roles obesity and rapid weight loss play in 

developing gallstones. Available at http://www.win.niddk.nih.gov/

publications/gallstones.htm. 

Weight Loss for Life. This booklet describes ways to lose weight 

and encourages healthy eating habits and regular physical activity. 

Available at http://www.win.niddk.nih.gov/publications/for_life.htm.

Additional Reading for Health Care Providers

Pharmacological and Surgical Treatment of Obesity: Evidence 

Report/Technology Assessment: Number 103. Shekelle PG, Morton 

SC, Maglione M, et al. Agency for Healthcare Research and Quality 

(AHRQ). AHRQ Publication Number 04–E028–1; 2004. Rockville, 

MD. This report reviews the scientific evidence on weight-loss drugs 

and bariatric surgery among children, youth, and adults. Available at 

http://www.ahrq.gov/downloads/pub/evidence/pdf/obespharm/obespharm.pdf. 

Additional Resource

American Society for Metabolic and Bariatric Surgery

100 SW 75th Street, Suite 201

Gainesville, FL 32607

Phone: 352–331–4900

Fax: 352–331–4975

Internet: http://www.asmbs.org

Weight-control

Information

Network

1 WIN Way

Bethesda, MD 20892–3665

Phone: 202–828–1025

Toll-free number: 1–877–946–4627

Fax: 202–828–1028

Email: 

win@info.niddk.nih.gov

Internet:

http://www.win.niddk.nih.gov

The Weight-control Information 

Network (WIN) is a service of 

NIDDK of the NIH, which is the 

Federal Government’s lead agency 

responsible for biomedical research 

on nutrition and obesity. Authorized 

by Congress (Public Law 103–43), 

WIN provides the general public, 

health professionals, the media, and 

Congress with up-to-date, sciencebased health information on weight 

control, obesity, physical activity, and 

related nutritional issues.

Publications produced by WIN are 

reviewed by both NIDDK scientists 

and outside experts. This fact sheet 

was also reviewed by Walter Pories, 

M.D., FACS, Professor of Surgery 

and Biochemistry, Brody School of 

Medicine at East Carolina University; 

and Thomas Inge, M.D., Ph.D., 

FACS, FAAP, Assistant Professor of 

Surgery and Pediatrics and Surgical 

Director, Comprehensive Weight 

Management Center, Cincinnati 

Children’s Hospital Medical Center. 

This text is not copyrighted. WIN 

encourages unlimited duplication and 

distribution of this fact sheet.

NIH Publication No. 08– 4006

March 2009

Updated June 2011