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Bariatric Surgery

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Bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss.

(See also Obesity.)

In the US, about 160,000 bariatric operations are done in each year. Development of safer laparoscopic approaches has made this surgery more popular.


To qualify for bariatric surgery, patients should

  • Have a body mass index (BMI) of > 40 kg/m2 or a BMI > 35 kg/m2 plus a serious complication (eg, diabetes, hypertension, obstructive sleep apnea, high-risk lipid profile)

  • Have acceptable operative risk

  • Be well-informed and motivated

  • Have unsuccessfully tried all reasonable nonsurgical methods to lose weight and manage obesity-associated complications

Although studies have shown that surgery causes remission of diabetes in patients with a BMI of 30 to 35, long-term data are limited, and the use of bariatric surgery is controversial in patients with a lower BMI.

Contraindications include

  • An uncontrolled psychiatric disorder such as major depression

  • Current drug or alcohol abuse

  • Cancer that is not in remission

  • Another life-threatening disorder

  • Inability to comply with nutritional requirements, including life-long vitamin replacement (when indicated)


The most common procedures done in the US include

  • Roux-en-Y gastric bypass (RYGB)

  • Sleeve gastrectomy (SG)

  • Adjustable gastric banding (AGB)

Most procedures are done laparoscopically, resulting in less pain and a shorter healing time than open surgery. Traditionally, bariatric surgery has been classified as restrictive and/or malabsorptive, referring to the presumptive mechanism of weight loss. However, other factors appear to contribute to weight loss; for example, RYGB (traditionally classified as malabsorptive) and SG (traditionally classified as restrictive) both result in metabolic or hormonal changes that favor satiety and weight loss and in other hormonal changes (eg, an increase in insulin release [incretin effect]) that appear to contribute to the rapid remission of diabetes. After RYGB (particularly) or SG, levels of GI hormones, such as glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), are increased, possibly contributing to satiety, weight loss, and remission of diabetes. Increased insulin sensitivity is evident immediately postoperatively, before significant weight loss occurs, suggesting that neurohormonal factors are prominent in remission of diabetes. A change in gut microbiome may also contribute to changes in weight after RYGB.

Roux-en-Y gastric bypass surgery

RYGB is usually done laparoscopically. A small part of the proximal stomach is detached from the rest, creating a stomach pouch of < 30 mL. Also, food bypasses part of the stomach and small intestine, where it is normally absorbed, reducing the amount of food and calories absorbed. The pouch is connected to the proximal jejunum; the opening between them is narrow, limiting the rate of gastric emptying. The segment of small intestine connected to the bypassed stomach is attached to the distal small intestine. This arrangement allows bile acids and pancreatic enzymes to mix with GI contents, limiting malabsorption and nutritional deficiencies.

RYGB is particularly effective in treating diabetes; remission rates are up to 62% after 6 yr.

For many patients who have had RYGB, eating high-fat and high-sugar foods can cause dumping syndrome; symptoms can include light-headedness, diaphoresis, nausea, abdominal pain, and diarrhea. Dumping syndrome may inhibit the consumption of such foods by adverse conditioning.

Roux-en-Y gastric bypass surgery.

Sleeve gastrectomy

In the past, SG was done only when patients are considered too high risk for procedures such as RYGB and biliopancreatic diversion (eg, patients with a BMI > 60), typically before one of these procedures or another similar procedure is done. However, because SG causes substantial and sustained weight loss, it is being used in the US as definitive treatment for severe obesity. Part of the stomach is removed, creating a tubular stomach passage. The procedure does not involve anatomic changes to the small intestine.

Mean excess weight loss tends to be higher than with that with AGB. Although SG is traditionally classified as a restrictive procedure, weight loss is probably also related to neurohormonal changes.

The most serious complication is gastric leak at the suture line; it occurs in 1 to 3% of patients.

Adjustable gastric banding

Use of AGB has dramatically decreased in the US. A band is placed around the upper part of the stomach to divide the stomach into a small upper pouch and a larger lower pouch. Typically, the band is adjusted 4 to 6 times by injecting saline into the band via a port that is placed subcutaneously. When saline is injected, the band expands, restricting the upper pouch of the stomach. As a result, the pouch can hold much less food, patients eat more slowly, and satiety occurs earlier. This procedure is usually done laparoscopically. Saline can be removed from the band if a complication occurs or if the band is overly restrictive.

Weight loss with the band varies and is related to the frequency of follow-up; more frequent follow-ups result in greater weight loss. Although postoperative morbidity and mortality are less than those with RYGB, long-term complications, including repeat operations, are more likely, possibly occurring in up to 15% of patients.

Adjustable gastric banding.

Biliopancreatic diversion with a duodenal switch

This procedure accounts for < 5% of bariatric procedures done in the US.

Part of the stomach is removed, causing restriction. The remaining part empties into the duodenum. The duodenum is cut and attached to the ileum, bypassing much of the small intestine, including the sphincter of Oddi (where bile acids and pancreatic enzymes enter); as a result, food absorption decreases. This procedure is technically demanding but can sometimes be done laparoscopically.

Malabsorption and nutritional deficiencies often develop.

Vertical banded gastroplasty

This procedure is no longer commonly done because complication rates are high and the resulting weight loss is insufficient. For this procedure, a stapler is used to divide the stomach into a small upper pouch and a larger lower pouch. A nonexpandable plastic band is placed around the opening where the upper pouch empties into the lower pouch.

Preoperative Evaluation

Preoperative evaluation consists of diagnosing and correcting comorbid conditions as much as possible, assessing readiness and ability to engage in lifestyle modification, and excluding contraindications to surgery. All patients should be evaluated by a dietician to review the postoperative diet and to assess their ability to make necessary lifestyle changes. All patients should also be evaluated by a psychologist or other qualified mental health care practitioner to identify any uncontrolled psychiatric disorder and any dependencies that would preclude surgery and to identify and discuss potential obstacles to adherence to lifestyle changes postoperatively.

Extensive preoperative evaluation is not routinely necessary, but preoperative testing may be necessary based on clinical findings, and measures to control certain conditions (eg, hypertension) or reduce risk may be taken.

  • Pulmonary: Patients at risk of obstructive sleep apnea based on clinical suspicion should be screened with polysomnography, and if obstructive sleep apnea is present, patients should be treated with continuous positive airway pressure (CPAP). This diagnosis indicates risk of cardiovascular morbidity and premature death. Smoking increases risk of pulmonary complications, ulcers, and GI bleeding postoperatively. Smoking should be stopped ≥ 8 wk before surgery and indefinitely thereafter.

  • Cardiac: Preoperative ECG is recommended, even for asymptomatic patients, to identify occult coronary artery disease. Even though obesity increases risk of pulmonary hypertension, echocardiography is not done routinely. Other cardiac testing is not done routinely; rather it is done based on the patient's risk factors for coronary artery disease, risk of surgery, and functional status. BP should be optimally controlled before surgery. During the perioperative period, risk of acute kidney disease is increased; thus, diuretics, ACE inhibitors, and angiotensin II receptor blockers (ARBs), if needed, should be used cautiously during this time.

  • GI: An upper GI series or endoscopy is usually done preoperatively. To reduce the risk of marginal ulcers, clinicians may test for and treat Helicobacter pylori infection, although evidence for the necessity of such treatment preoperatively is inconsistent.

  • Hepatic: Increased liver enzymes, especially ALT, are common among candidates for bariatric surgery and often indicate fatty liver disease. Levels of > 2 to 3 times the upper limit of normal should not be assumed to result from fatty liver and should prompt an investigation for other causes of abnormal liver enzyme levels. If prophylactic cholecystectomy is planned during bariatric surgery (to decrease risk of cholelithiasis), liver ultrasonography may be done.

  • Metabolic bone disease: Obese patients are at risk of vitamin D deficiency and metabolic bone disease, sometimes with secondary hyperparathyroidism. Patients should be screened and treated for these disorders before surgery, particularly because vitamin D deficiency is common preoperatively and poor absorption develops postoperatively.

  • Diabetes: Because poorly controlled diabetes increases the risk of adverse surgical outcomes, glycemic control should be optimized before surgery.

  • Nutrition: Obese patients are at risk of nutritional deficiencies, which can be exacerbated postoperatively because food preferences and tolerance change, stomach acidity changes, and absorption from the small intestine is decreased. Routine measurement of vitamin D, vitamin B12, folate, and iron levels is recommended. For certain patients, measuring levels of other nutrients, such as thiamin (vitamin B1), may also be indicated.


Perioperative risks are lowest when bariatric surgery is done in an accredited center.

Complications include

  • Gastric and/or anastomotic leaks (in 1 to 3%)

  • Pulmonary complications (eg, ventilator dependence, pneumonia, pulmonary embolism)

  • MI

  • Wound infection

  • Incisional hernia

  • Small-bowel obstruction

  • GI bleeding

  • Ventral hernia

  • Deep venous thrombosis

These complications can cause significant morbidity, prolong hospitalization, and increase costs. Tachycardia may be the only early sign of anastomotic leak.

Later problems may include prolonged nausea and vomiting secondary to small-bowel obstruction and anastomotic stenosis.

Nutritional deficiencies (eg, protein-energy undernutrition, vitamin B12 deficiency, iron deficiency) may result from inadequate intake, inadequate supplementation, or malabsorption. Malodorous flatulence, diarrhea, or both may develop, particularly after malabsorptive procedures. Calcium and vitamin D absorption may be impaired, causing deficiencies and sometimes hypocalcemia and secondary hyperparathyroidism. With prolonged vomiting, thiamin deficiency may occur.

Patients may have symptoms of reflux, especially after SG. During rapid weight loss, cholelithiasis (often symptomatic), gout, and nephrolithiasis may develop.

Incidence of psychologic disorders such as depression is increased in patients having bariatric surgery. A 2016 meta-analysis confirmed this increase in preoperative depression and reported a postoperative decrease in the prevalence and severity of depression (1).One large study suggested that the risk of suicide in patients who had bariatric surgery was increased compared with that in controls (2.7 vs 1.2 per 10,000 person-yr; hazard ratio 1.71 [0.69 to 4.25]; P value = 0.25 [2]). Incidence of alcohol use disorder also appears to be increased after bariatric surgery (3).

Eating habits may be disordered. Adjusting to new eating habits can be difficult.

Risks references


In hospitals accredited by the American Society of Bariatric Surgery as centers of excellence (COE), overall 30-day mortality is 0.2 to 0.3%. However, some data indicate that lower rates of serious complications are predicted more accurately by the number of procedures done in the hospital and by the surgeon than by COE status.

Mortality is higher with RYGB than laparoscopic AGB and higher with open procedures (2.1%) than laparoscopic procedures (0.2%). Factors that predict higher risk of mortality include a history of deep venous thrombosis or pulmonary embolism, obstructive sleep apnea, and poor functional status. Other factors such as severe obesity (BMI > 50), older age, and male sex have also been associated with higher risk, but the evidence is inconsistent.

Average excess weight loss depends on the procedure.

For laparoscopic AGB, weight loss is

  • 45 to 72% at 3 to 6 yr

  • 14 to 60% at 7 to 10 yr

  • About 47% at 15 yr

Percentage of weight loss is related to the frequency of follow-ups and number of band adjustments. Patients with a lower BMI tend to lose more excess weight than those with a higher BMI.

For SG, weight loss is

  • 33 to 58% at 2 yr

  • 58 to 72% at 3 to 6 yr

Longer-term data are not available.

For RYGB, weight loss is

  • 50 to 65% after 2 yr

Weight loss after RYGB is maintained for up to 10 yr.

Comorbid conditions that tend to abate or resolve after bariatric surgery include cardiovascular risk factors (eg, dyslipidemia, hypertension, diabetes), cardiovascular disorders, diabetes, obstructive sleep apnea, osteoarthritis, and depression. Diabetes is particularly likely to remit (eg, with RYGB, up to 62% of patients at 6 yr). All-cause mortality decreases by 25%, primarily because cardiovascular and cancer mortality is reduced.


Regular, long-term follow-up helps ensure adequate weight loss and prevent complications. After RYGB or SG, patients should be monitored every 4 to 12 wk during the period of rapid weight loss (usually about the first 6 mo after surgery), then every 6 to 12 mo thereafter. With laparoscopic AGB, results appear to be optimal when patients are monitored and the band is adjusted at least 6 times during the first year after surgery.

Weight and BP are checked, and eating habits are reviewed. Blood tests (usually CBC, electrolytes, glucose, BUN, creatinine, albumin, and protein and liver function tests) are done at regular intervals. Glycosylated Hb (HbA1c) and fasting lipid levels should be monitored if they were abnormal before surgery. Depending on the type of procedure, vitamin and mineral levels, including calcium, vitamin D, vitamin B12, folate, iron, and thiamin (vitamin B1), may need to be monitored. Because secondary hyperparathyroidism is a risk, parathyroid hormone levels should also be monitored. Bone density should be measured after SG and RYGB.

Clinicians should check for any changes in response to antihypertensives, insulin, oral hypoglycemics, or lipid-lowering drugs during the period of rapid weight loss after surgery.

Patients should be regularly evaluated for gout, cholelithiasis, and nephrolithiasis, all of which can develop after bariatric surgery. Prophylactic ursodiol reduces risk of cholelithiasis and should be offered after bariatric surgery. Patients should also be regularly screened for depression and alcohol use, particularly if alcohol use was heavy preoperatively.

To minimize risk of hypoglycemia (due to increased insulin sensitivity after bariatric surgery) in patients with diabetes, clinicians should adjust the dose of insulin and decrease the dose of oral hypoglycemics (particularly sulfonylureas) or stop them after RYGB and SG.

Key Points

  • Consider weight loss surgery if patients are motivated, have not succeeded using nonsurgical treatments, and have a BMI of > 40 kg/m2 or a BMI of > 35 kg/m2 plus a serious complication (eg, diabetes, hypertension, obstructive sleep apnea, high-risk lipid profile).

  • Weight loss surgery is contraindicated if patients have an uncontrolled psychiatric disorder (eg, major depression), drug or alcohol abuse, cancer that is not in remission, or another life-threatening disorder or if they cannot comply with nutritional requirements (including life-long vitamin replacement when indicated).

  • The most common procedure is Roux-en-Y gastric bypass, followed by sleeve gastrectomy; use of adjustable gastric banding has decreased dramatically in the US.

  • Monitor patients regularly after surgery for maintenance of weight loss, resolution of weight-related comorbid disorders, and complications of surgery (eg, nutritional deficiencies, metabolic bone disease, gout, cholelithiasis, nephrolithiasis, depression, alcohol abuse).

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