Gastric bypass surgery
Gastric bypass procedures (GBP) are any of a group of similar operations used to treat morbid obesity—the severe accumulation of excess weight as fatty tissue—and the health problems (comorbidities) it causes. Bariatric surgery is the term encompassing all of the surgical treatments for morbid obesity, not just gastric bypasses, which make up only one class of such operations.
A gastric bypass first divides the stomach into a small upper pouch and a much larger, lower "remnant" pouch and then re-arranges the small intestine to allow both pouches to stay connected to it. Surgeons have developed several different ways to reconnect the intestine, thus leading to several different GBP names. Any GBP leads to a marked reduction in the functional volume of the stomach, accompanied by an altered physiological and psychological response to food. The resulting weight loss, typically dramatic, markedly reduces comorbidities. The death rate is reduced by up to 40%.
Life-threatening health problems arise from obesity as a consequence of its mechanical or metabolic effects. These comorbidities may in turn lead to severe deterioration of health, shortened life expectancy, and lower quality of life.
Major comorbidities include:
- Atherosclerotic cardiovascular disease. Obesity is not only associated with the occurrence of hypercholesterolemia and hypertriglyceridemia, but it is also a factor in the occurrence of atherosclerosis, the deposition of fats within the walls of the blood vessels. This leads to conditions such as coronary artery disease, congestive heart failure, and "hardening of the arteries." This group of conditions is a leading cause of death in the United States.
- Diabetes mellitus type 2 occurs mostly in middle and old age, but it is up to 40 times more likely in those who are severely overweight. It is associated with ASCVD, kidney failure, blindness, nerve damage, and amputations of the extremities, and is also a leading overall cause of death in the United States. Dysmetabolic Syndrome X, a pre-diabetic condition often associated with obesity, is accompanied by elevated levels of insulin in the blood and a high incidence of early development of coronary heart disease.
- Essential hypertension or "high blood pressure", is much more common in obese individuals. It can lead to early development of ASCVD, as well as to kidney disease. Weight loss is considered to be an important feature of treatment.
- Obstructive sleep apnea (OSA) Persons with this condition tend to suffer from airway obstruction when asleep, as the muscles relax and the weight and bulk of tissues collapses the throat passages. An observer notices loud snoring, frequent periods when breathing ceases (apneas), and episodes of restlessness and partial awakening. The afflicted patient is often unaware of the nature of the problem, but may notice frequent awakening at night, dry mouth, a sense of having slept poorly, daytime drowsiness and fatigue, or inappropriate sleeping (such as at work, in meetings, or while driving). This condition has a significant associated mortality.
- Gastroesophageal reflux disease (GERD) is characterized by regurgitation (reflux) of acid and gastric contents into the esophagus, and sometimes into the back of the throat. Gastric acid and bile are very corrosive to the lining membrane of the esophagus, and cause it to become inflamed (esophagitis) and sometimes scarred (esophageal stricture). Reflux which occurs while sleeping can lead to sudden coughing and choking at night, a burning sensation in the throat (pyrosis), and inhalation of acid and stomach contents into the lungs, with the risk of hoarseness, bronchitis, pneumonia, lung abscess and lung scarring. GERD is often associated with development of asthma, and causation of asthmatic attacks, and may also be aggravated by OSA.
- Gallbladder disease is much more likely in obese individuals, being associated with formation of gallstones, usually composed of crystallized cholesterol, within the gallbladder. Although readily treatable by removal of the gallbladder (cholecystectomy), it may lead to life-threatening problems such as obstruction of the ducts from the liver, jaundice, and inflammation of the pancreas (gallstone pancreatitis).
- Liver disease is present in some degree in 90% of persons who undergo bariatric surgery, usually a manifestation of the metabolic effects of obesity on the liver. This may take the form of large fat globules within the liver cells (steatosis), chronic inflammation of the liver (steatohepatitis), and in a few instances, cirrhosis of the liver. The latter condition may lead to liver failure and the need for a liver transplant.
- Venous thromboembolic disease affects the legs, and causes swelling, thickening and discoloration of the skin, and ulceration of the skin. This condition begins with damage to the veins of the legs, associated with formation of blood clots (thrombophlebitis), often associated with an injury, a pregnancy (even use of birth-control pills or hormones), or a surgical operation. When a newly formed blood clot breaks loose, and floats through the veins to the heart and lungs, it is called a Pulmonary embolus, which may sometimes be fatal within minutes. More commonly, the blood clot remains in place locally, and heals by becoming a scar, which permanently damages the vein. Once damaged, the veins cannot fully function to return blood to the heart, and increased venous pressure in the legs causes swelling, impaired circulation in the skin, and sometimes skin breakdown. Obesity is a major risk factor in development of VTE, and may also aggravate the increased venous pressure in the legs.
- Degenerative disc disease is a progressive "wearing-out" of the cartilaginous disks between the vertebral bones of the spine. It occurs more often and earlier in life in obese persons, due to the markedly increased mechanical stress on the disks from the extra weight. Its most common sign is chronic low back pain, which may be disabling. This condition is also associated with sciatica, lumbar spondylosis, and spinal stenosis.
- Degenerative disease of the weight-bearing joints, or osteoarthritis, affecting the hips, knees, ankles and feet, occurs earlier in life, and in greater degree, in obese individuals, due to the mechanical stresses of excess weight. Joint pain, loss of mobility, and joint replacement surgery are much more likely in obese persons.
Gastric Bypass is indicated for the surgical treatment of morbid obesity, a diagnosis which is made when the patient is seriously obese, has been unable to achieve satisfactory and sustained weight loss by dietary efforts, and is suffering from co-morbid conditions which are either life-threatening or a serious impairment to the quality of life.
In the past, serious obesity was interpreted to mean weighing at least 100 pounds (45 kg) more than the "ideal body weight", an actuarially determined body weight at which one was estimated to be likely to live the longest, as determined by the life insurance industry. This criterion failed for persons of short stature.
In 1991, a Consensus Panel of physicians was sponsored by the National Institutes of Health, and its recommendations have set the current standard for consideration of surgical treatment, the body mass index (BMI). The BMI is defined as the body weight (in kilograms), divided by the square of the height (in meters). The result is expressed as a number usually between 20 and 70, in units of kilograms per square meter.
The Consensus Panel of the National Institutes of Health (NIH) recommended the following criteria for consideration of bariatric surgery, including gastric bypass procedures:
- People who have a body mass index (BMI) of 40 or higher. Or,
- People with a BMI of 35 or higher with one or more related comorbid conditions.
The Consensus Panel also emphasized the necessity of multidisciplinary care of the bariatric surgical patient, by a team of physicians and therapists, to manage associated co-morbidities, nutrition, physical activity, behavior and psychological needs. The surgical procedure is best regarded as a tool which enables the patient to alter lifestyle and eating habits, and to achieve effective and permanent management of their obesity and eating behavior.
Since 1991, major developments in the field of bariatric surgery, particularly laparoscopy, have outdated some of the conclusions of the NIH panel. In 2004, a Consensus Conference was sponsored by the American Society for Bariatric Surgery (ASBS), which updated the evidence and the conclusions of the NIH panel. This Conference, composed of physicians and scientists of many disciplines, both surgical and non-surgical, reached several conclusions, amongst which were:
- Bariatric surgery is the most effective treatment for morbid obesity
- Gastric bypass is one of four types of operations for morbid obesity.
- Laparoscopic surgery is equally effective and as safe as open surgery.
- Patients should undergo comprehensive pre-operative evaluation, and have multi-disciplinary support, for optimum outcome.
The gastric bypass, in its various forms, accounts for a large majority of the bariatric surgical procedures performed. It is estimated that 140,000 such operations were performed in the United States in 2005. An increasing number of these operations are now performed by limited access techniques, termed "laparoscopy".
Laparoscopic surgery is performed using several small incisions, or ports, one of which conveys a surgical telescope connected to a video camera, and others permit access of specialized operating instruments. The surgeon actually views his operation on a video screen. The method is also called limited access surgery, reflecting both the limitation on handling and feeling tissues, and also the limited resolution and two-dimensionality of the video image. With experience, a skilled laparoscopic surgeon can perform most procedures as expeditiously as with an open incision — with the option of using an incision should the need arise.
The Laparoscopic Gastric Bypass, Roux-en-Y, first performed in 1993, is regarded as one of the most difficult procedures to perform by limited access techniques, but use of this method has greatly popularized the operation, with benefits which include shortened hospital stay, reduced discomfort, shorter recovery time, less scarring, and minimal risk of incisional hernia.
The gastric bypass procedure consists in essence of:
- Creation of a small, (15–30 mL/1–2 tbsp) thumb-sized pouch from the upper stomach, accompanied by bypass of the remaining stomach (about 400 mL and variable). This restricts the volume of food which can be eaten. The stomach may simply be partitioned (typically by the use of surgical staples), or it may be totally divided into two parts (also with staplers). Total division is usually advocated, to reduce the possibility that the two parts of the stomach will heal back together ("fistulize"), negating the operation.
- Re-construction of the GI tract to enable drainage of both segments of the stomach. The technique of this reconstruction produces several variants of the operation, which differ in the lengths of small bowel used, the degree to which food absorption is affected, and the likelihood of adverse nutritional effects.
Variations of the gastric bypass
Gastric bypass, Roux en-Y (proximal)
This variant is the most commonly employed gastric bypass technique, and is by far the most commonly performed bariatric procedure in the United States. It is the operation which is least likely to result in nutritional difficulties. The small bowel is divided about 45 cm (18 in) below the lower stomach outlet, and is re-arranged into a Y-configuration, to enable outflow of food from the small upper stomach pouch, via a "Roux limb". In the proximal version, the Y-intersection is formed near the upper (proximal) end of the small bowel. The Roux limb is constructed with a length of 80 to 150 cm (30 to 60 inches), preserving most of the small bowel for absorption of nutrients. The patient experiences very rapid onset of a sense of stomach-fullness, followed by a feeling of growing satiety, or "indifference" to food, shortly after the start of a meal.
Gastric bypass, Roux en-Y (distal)
The normal small bowel is 600 to 1000 cm (20 to 33 feet) in length. As the Y-connection is moved farther down the Gastrointestinal tract, the amount of bowel capable of fully absorbing nutrients is progressively reduced, in pursuit of greater effectiveness of the operation. The Y-connection is formed much closer to the lower (distal) end of the small bowel, usually 100 to 150 cm (40 to 60 inches) from the lower end of the bowel, causing reduced absorption (mal-absorption) of food, primarily of fats and starches, but also of various minerals, and the fat-soluble vitamins. The unabsorbed fats and starches pass into the large intestine, where bacterial actions may act on them to produce irritants and malodorous gases. These increasing nutritional effects are traded for a relatively modest increase in total weight loss.
Loop Gastric bypass ("Mini-gastric bypass")
The first use of the gastric bypass, in 1967, used a loop of small bowel for re-construction, rather than a Y-construction as is prevalent today. Although simpler to create, this approach allowed bile and pancreatic enzymes from the small bowel to enter the esophagus, sometimes causing severe inflammation and ulceration of either the stomach or the lower esophagus. If a leak into the abdomen occurs, this corrosive fluid can cause severe consequences. Numerous studies show the loop reconstruction (Billroth II gastrojejunostomy) works more safely when placed low on the stomach, but can be a disaster when placed adjacent to the esophagus. Thus even today thousands of "loops" are used for general surgical procedures such as ulcer surgery, stomach cancer and injury to the stomach, but bariatric surgeons abandoned use of the construction in the 1970s, when it was recognized that its risk is not justified for weight management.
The Mini-Gastric Bypass, which uses the loop reconstruction, has been suggested as an alternative to the Roux en-Y procedure, due to the simplicity of its construction, which reduced the challenge of laparoscopic surgery. It is claimed that construction of a long tubular gastric pouch reduces the risk of inflammatory complications, and renders it as safe as the RNY technique. Most bariatric surgeons shun the procedure, and most would assert that it remains unproven and investigational in nature at this time.
Physiology of the gastric bypass
The gastric bypass reduces the size of the stomach by well over 90%. A normal stomach can stretch, sometimes to over 1000 ml, while the pouch of the gastric bypass may be 15 ml in size. The Gastric Bypass pouch is usually formed from the part of the stomach which is least susceptible to stretching. That, and its small original size, prevents any significant long-term change in pouch volume. What does change, over time, is the size of the connection between stomach and bowel, and the ability of the small bowel to hold a greater volume of food. Over time, the functional capacity of the pouch increases; by that time, weight loss has occurred, and the increased capacity serves to allow maintenance of a lower body weight.
When the patient ingests just a small amount of food, the first response is a stretching of the wall of the stomach pouch, stimulating nerves which tell the brain that the stomach is full. The patient feels a sensation of fullness, as if they had just eaten a large meal — but with just a thumbful of food. Most people do not stop eating simply in response to a feeling of fullness, but the patient rapidly learns that subsequent bites must be eaten very slowly and carefully, to avoid increasing discomfort, or even vomiting.
Normally when we eat, food passes out of the stomach into the duodenum after about 30 minutes. When it reaches the lower end of the duodenum, a new hormonal message is generated, telling the brain that enough food has been eaten. The person with a normal GI tract experiences this hormone release as a sense of satisfaction or "satiety" — a feeling of indifference toward eating any more. Recently, a hormone called ghrelin has been discovered, which may contribute to this effect.
To gain the maximum benefit from this physiology, it is important that the patient eat only at mealtimes, 2 to 3 meals daily, and avoid snacks and grazing between meals, which can effectively "bypass the bypass". This requires a change in eating behavior, and alteration of long-acquired habits for finding food. In almost every case where weight gain occurs late after surgery, capacity for a meal has not greatly increased. The cause of regaining weight is eating between meals, usually high-caloric snack foods. There is no known operation which can completely counteract the adverse effects of destructive eating behavior.
Any major surgery involves the potential for complications — adverse events which increase risk, hospital stay, and mortality. Some complications are common to all abdominal operations, while some are specific to bariatric surgery. A person who chooses to undergo bariatric surgery should know about these risks.
Mortality & Complication Rates
A recent large multi-center study reported that, in experienced hands, the overall complication rate of this type of surgery ranges from 7% for laparoscopic procedures to 14.5% for operations through open incisions, during the 30 days following surgery. Mortality for this study was 0% in 401 laparoscopic cases, and 0.6% in 955 open procedures. Similar mortality rates – 30-day mortality of 0.11%, and 90-day mortality of 0.3% – have been recorded in the U.S. Centers of Excellence program, the results from 33,117 operations at 106 centers.
Mortality is affected by complications, which in turn are affected by pre-existing risk factors such as degree of obesity, heart disease, obstructive sleep apnea, diabetes mellitus, and history of prior pulmonary embolism. It is also affected by the experience of the operating surgeon: the "learning curve" for laparoscopic bariatric surgery is estimated to be about 100 cases, and inexperienced surgeons have been shown in several studies to have a significantly higher rate of complications and mortality. Unfortunately, the way a surgeon becomes experienced in dealing with problems is by encountering those problems over time.
Complications of abdominal surgery
Infection of the incisions, or of the inside of the abdomen (peritonitis, abscess) may occur, due to release of bacteria from the bowel during the operation. Nosocomial infection, such as pneumonia, bladder or kidney infections, and sepsis (bloodborne infection) are also possible. Effective short-term use of antibiotics, diligent respiratory therapy, and encouragement of activity within a few hours after surgery, can reduce the risks of infections.
Many blood vessels must be cut in order to divide the stomach and to move the bowel. Any of these may later begin bleeding, either into the abdomen (intra-abdominal hemorrhage), or into the bowel itself (gastrointestinal hemorrhage). Transfusions may be needed, and re-operation is sometimes necessary. Use of blood thinners, to prevent venous thromboembolic disease, may actually increase the risk of hemorrhage slightly.
A hernia is an abnormal opening, either within the abdomen, or through the abdominal wall muscles. An internal hernia may result from surgery, and re-arrangement of the bowel, and is mainly significant as a cause of bowel obstruction. An incisional hernia occurs when a surgical incision does not heal well; the muscles of the abdomen separate and allow protrusion of a sac-like membrane, which may contain bowel or other abdominal contents, and which can be painful and unsightly. The risk of abdominal wall hernia is markedly decreased in laparoscopic surgery.
Abdominal surgery always results in some scarring of the bowel, called adhesions. A hernia, either internal or through the abdominal wall, may also result. When bowel becomes trapped by adhesions or a hernia, it may become kinked and obstructed, sometimes many years after the original procedure. Usually an operation is necessary, to correct this problem.
Any injury, such as a surgical operation, causes the body to increase the coagulation of the blood. Simultaneously, activity may be reduced. There is an increased probability of formation of clots in the veins of the legs, or sometimes the pelvis, particularly in the morbidly obese patient. A clot which breaks free and floats to the lungs is called a pulmonary embolus, a very dangerous occurrence. Commonly, blood thinners are administered before surgery, to reduce the probability of this type of complication.
Complications of gastric bypass
An anastomosis is a surgical connection between the stomach and bowel, or between two parts of the bowel. The surgeon attempts to create a water-tight connection by connecting the two organs with either staples or sutures, either of which actually makes a hole in the bowel wall. The surgeon will rely on the healing power of the body, and its ability to create a seal like a self-sealing tire, to succeed with the surgery. If that seal fails to form, for any reason, fluid from within the gastrointestinal tract can leak into the sterile abdominal cavity and give rise to infection and abscess formation. Leakage of an anastomosis can occur in about 2% of gastric bypass procedures, usually at the stomach-bowel connection. Sometimes leakage can be treated with antibiotics, and sometimes it will require immediate re-operation. It is usually safer to re-operate if an infection cannot be definitely controlled immediately.
As the anastomosis heals, it forms scar tissue, which naturally tends to shrink ("contract") over time, making the opening smaller. This is called a "stricture". Usually, the passage of food through an anastomosis will keep it stretched open, but if the inflammation and healing process outpaces the stretching process, scarring may make the opening so small that even liquids can no longer pass through it. The solution is a procedure called gastroendoscopy, and stretching of the connection by inflating a balloon inside it. Sometimes this manipulation may have to be performed more than once to achieve lasting correction.
Normally, the pyloric valve at the lower end of the stomach regulates the release of food into the bowel. When the Gastric Bypass patient eats a sugary food, the sugar passes rapidly into the bowel, where it gives rise to a physiological reaction called dumping syndrome. An affected person feels his heart beating rapidly and forcefully, breaks into a cold sweat, gets a feeling of butterflies in the stomach, and has a "sky is falling" type of anxiety. He usually has to lie down, and is very uncomfortable for about 30 to 45 minutes. Diarrhea may then follow. The dumping syndrome is a response to a behavior which the patient should not be doing anyway: eating sugary foods. It is not life-threatening, and may assist one in making healthier food choices.
Neurological complications "multiple nutritional deficiencies, but their correction did not often yield dramatic results". Neurological complications have been labeled in older studies as:
Proteins are essential food substances, contained in foods such as meat, fish and poultry, dairy products, soy, and eggs. With reduced ability to eat a large volume of food, gastric bypass patients must focus on eating their protein requirements first, and with each meal. Proximal GBP rarely leads to protein deficiency if this simple precaution is followed. Distal GBP is more likely to lead to protein deficiency, particularly if fat intake is excessive, and the position of the Y-connection is farther downstream. In some cases, surgeons may recommend use of a liquid protein supplement.
Protein malnutrition is a real risk. Some patients suffer troublesome vomiting after surgery, until their GI tract adjusts to the changes, and cannot eat adequate amounts even with 6 meals a day. Many patients require protein supplementation during the early phases of rapid weight loss, to prevent excessive loss of muscle mass.
The profound weight loss which occurs after bariatric surgery is due to taking in much less energy (calories) than the body needs to use every day. Fat tissue must be burned, to offset the deficit, and weight loss results. Eventually, as the body becomes smaller, its energy requirements are decreased, while the patient simultaneously finds it possible to eat somewhat more food. When the energy consumed is equal to the calories eaten, weight loss will stop. Proximal GBP typically results in loss of 60 to 80% of excess body weight, and very rarely leads to excessive weight loss. The risk of excessive weight loss is slightly greater with Distal GBP.
Vitamins are normally contained in the foods we eat, as well as any supplements we may choose to take. The amount of food which will be eaten after GBP is severely reduced, and vitamin content is correspondingly reduced. Supplements should therefore be taken, to completely cover minimum daily requirements of all vitamins and minerals. Absorption of most vitamins is not seriously affected, after Proximal GBP, although Vitamin B-12 may not be well-absorbed in some persons. After the Distal GBP, fat-soluble vitamins A, D and E may not be well-absorbed, particularly if fat intake is large. Water-dispersed forms of these vitamins may be indicated, on specific physician recommendation.
Thiamine deficiency or beriberi may happen according to a systematic review This is a result of a change in the role food plays in their emotional well-being. Many morbidly obese people use food as an emotional crutch, and the strict limitations on the diet can place great emotional strain on the patient. Energy levels in the period following the surgery will be low. This is due again to the restriction of food intake, but the negative change in emotional state will also have an impact here. It may take as long as three months for emotional levels to rebound. Muscular weakness in the months following surgery is common. This is caused by a number of factors, including a restriction on protein intake, a resulting loss in muscle mass and decline in energy levels. The weakness may result in balance problems, difficulty climbing stairs or lifting heavy objects, and increased fatigue following simple physical tasks. Many of these issues will pass over time as food intake gradually increases. However, the first months following the surgery can be very difficult, an issue not often mentioned by physicians suggesting the surgery. The benefits and risks of this surgery are well established; however, the psychological effects are not well understood, and potential patients should ensure a strong support system before agreeing to the procedure.
Centers of excellence
Persons who are considering bariatric surgery should find an experienced and well-qualified surgeon at a well-equipped hospital, which has a network of collaborating healthcare professionals to assist them in the complete care of the patient's medical, nutritional, and psychological needs. There are two national certification programs which evaluate bariatric surgery centers for:
- Surgeon experience
- Hospital facilities
- Multidisciplinary care available
- Complication and mortality rates
- Long term follow-up program
SRC Centers of Excellence
The American Society for Metabolic & Bariatric Surgery established the independent Surgical Review Corporation to certify Centers of Excellence. Over 315 qualified bariatric programs, with nearly 560 surgeons (as of January 2008), have been qualified nationwide.
ACS Bariatric Surgery Center Network
The American College of Surgeons Bariatric Surgery Center Network is a listing of centers approved by that organization.
International Federation for the Surgery of Obesity
This multinational organization unites bariatric surgeons of many countries. Many leading American surgeons are also members of the American Society for Metabolic & Bariatric Surgery(ASMBS). Persons seeking a qualified surgeon may check the ASMBS website, or a listing of IFSO Councils by country.
- ↑ Adams TD, Gress RE, Smith SC, et al, Long-term mortality after gastric bypass surgery. N Engl J Med. 2007 Aug 23;357(8):753-61. PMID 17715409
- ↑ Sjostrom L, Narbro K, Sjostrom CD, et al. Effects of bariatric surgery on mortality in Swedish obese subjects. N Engl J Med. 2007 Aug 23;357(8):741-52. PMID 17715408
- ↑ Juhasz-Pocsine K, Rudnicki SA, Archer RL, Harik SI. Neurologic complications of gastric bypass surgery for morbid obesity. Neurology. 2007 May 22;68(21):1843-50. PMID: PMID 17515548
- ↑ 4.0 4.1 Chang CG, Adams-Huet B, Provost DA. Acute post-gastric reduction surgery (APGARS) neuropathy. Obes Surg. 2004 Feb;14(2):182-9. PMID 15018746.
- ↑ Koffman BM, Greenfield LJ, Ali II, Pirzada NA. Neurologic complications after surgery for obesity. Muscle Nerve. 2006 Feb;33(2):166-76. PMID 15973660
- ↑ Delin, CR; Watts, JM; Saebel, JL; Anderson, PG (1997), "Eating behavior and the experience of hunger following gastric bypass surgery for morbid obesity.", Obesity Surgery, 7 (5): 405–13, PMID 9730494
- ↑ Surgical Review Corporation Centers of Excellence
- ↑ ACS Bariatric Surgery Center Network
- ↑ ASBS Member Listing
- ↑ IFSO National Councils
- Buchwald, H; Cowan, GSM; Pories, WJ (2007), Surgical Management of Obesity, Saunders Elsevier, ISBN 978-1416000891
- Buchwald, H (2005), "Bariatric surgery for morbid obesity: health implications for patients, health professionals, and third-party payers.", J Am Coll Surg, 200 (4): 593–604, PMID 15804474
- Christou, N; Sampalis, J; Liberman, M; Look, D; Auger, S; McLean, A; MacLean, L (2004), "Surgery decreases long-term mortality, morbidity, and health care use in morbidly obese patients.", Ann Surg, 240 (3): 416–23, discussion 423-4, PMID 15319713 text
- Wittgrove, AC; Clark, GW (2000), "Laparoscopic Gastric Bypass, Roux en-Y – 500 Patients: Technique and Results with 3-60 Months Follow-up.", Obesity Surgery, 10: 233–239
- Fontaine, KR; et al. (2003), "Years of life lost to obesity.", JAMA, 289: 187–193
- Peeters, A; Barendregt, J; Willekens, F; Mackenbach, J; Al-Mamun, A; Bonneux, L (2003), "Obesity in adulthood and its consequences for life expectancy: a life-table analysis.", Ann Intern Med, 138 (1): 24–32, PMID 12513041 text (PDF)
- Hutter, MM; Randall, S; Khuri, SF; Henderson, WG; Abbott, WM; Warshaw, AL (2006), "Laparoscopic Versus Open Gastric Bypass for Morbid Obesity: A Multicenter, Prospective, Risk-Adjusted Analysis From the National Surgical Quality Improvement Program", Annals of Surgery, 243 (5): 657–666, PMID 16633001
- American Society for Metabolic & Bariatric Surgery, an association of healthcare professionals with demonstrated interest and expertise in the surgical management of obesity.
- ASBS Consensus Conference Statement – 2004
- NIH – Gastrointestinal Surgery for Obesity - info site
- NIH Medline Plus – Multiple Links to articles, videos about bariatric surgery
- Original NIH Consensus Panel Statement – 1991 This report contains useful information, but is now 17 years out-of-date, and was written before laparoscopic surgery became available.
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