Bariatric Surgery

Updated: Mar 16, 2023
  • Author: Alan A Saber, MD, MS, FACS, FASMBS; Chief Editor: John Geibel, MD, MSc, DSc, AGAF  more...
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Practice Essentials

Obesity is a major health problem worldwide and has reached an epidemic proportion in the Western society. Evidence continues to accumulate that obesity is a major risk factor for many diseases and is associated with significant morbidity and mortality.

The most widely accepted measure of obesity has been the body mass index (BMI). This number is calculated by dividing a patient's mass (kg) by his or her height (m2). A normal BMI has been considered to lie the range of 18.5-24.9 kg/m2. A BMI of 25-29.9 kg/m2 has been considered overweight. A BMI of 30 kg/m2 or greater has been classified as obese; this classification has been further subdivided into class I, II, or III obesity.

Considering other factors (eg, total muscle mass, waist circumference) besides the BMI may be important. For example, an extremely muscular individual may have an elevated BMI without being considered overweight. Waist circumference has been shown to be an excellent indicator of abdominal fat mass. A circumference of greater than 88 cm (35 in.) in women or greater than 102 cm (40 in.) in men strongly correlates with an increased risk of obesity-related disease.

Bariatric surgery is currently the only modality that provides a significant, sustained weight loss for morbidly obese patients, with resultant improvement in obesity-related comorbidities. A prospective, controlled Swedish study involving 4047 obese patients, half of whom had undergone bariatric procedures, followed up over 14.7 years, found that compared to usual care, bariatric surgery was associated with a significantly reduced number of cardiovascular deaths and a lower incidence of cardiovascular events in obese adults. [1]

In 1954, Kremen and Linner introduced jejunoileal bypass, the first effective surgery for obesity in the United States. In this procedure, the proximal jejunum was connected directly to the distal ileum, bypassing 90% of the small intestine out of the intestinal stream of ingested nutrients (blind loop). The procedure induced a state of malabsorption, which led to significant weight loss.

However, many patients developed complications secondary to malabsorption (eg, steatorrhea, diarrhea, vitamin deficiencies, oxalosis) or due to the toxic overgrowth of bacteria in the bypassed intestine (eg, liver failure, severe arthritis, skin problems). Consequently, many patients have required reversal of the procedure, and the procedure has been abandoned. This led to a search for better operations.

Modifications in the original procedures and the development of new techniques led to the following three basic concepts for bariatric surgery (see Surgical Therapy):

  • Gastric restriction (adjustable gastric banding, sleeve gastrectomy)
  • Gastric restriction with mild malabsorption (Roux-en-Y gastric bypass)
  • Combination of mild gastric restriction and malabsorption (duodenal switch)

The field of bariatric surgery has been enriched by data from numerous clinical investigations and experience. The direction of future clinical investigations are proceeding in a number of directions, including the following:

  • Controlled, prospective, intervention studies
  • Establishment of a major prospective database to study bariatric surgery outcomes
  • Establishment of a pediatric (adolescent) bariatric surgery registry
  • Performance of randomized clinical trials to compare the safety and efficacy of different operative procedures
  • Controlled studies of new operative modalities (eg, gastric pacing) and nonoperative modalities of treatment
  • Study by meta-analysis of outcomes of comorbid conditions of morbid obesity
  • Study of the socioeconomic outcomes of bariatric surgery
  • Study by stratified risk assessment of the risk-to-benefit ratio of treating morbid obesity with bariatric surgery and without bariatric surgery

For patient education resources, see the Healthy Living Center, as well as Obesity and Surgery in the Treatment of Obesity.



Obesity occurs as the result of an imbalance between energy expenditure and caloric intake. This imbalance has been thought to be under genetic and environmental influence. The discovery of immunologic abnormalities in obesity that are related to the leptin-proopiomelanocortin system and elevated tumor necrosis factor alpha (TNF-α) brought a new perspective to the understanding of obesity.

Leptin (from Greek leptos, "thin") is a hormone made primarily in adipocytes. The circulating leptin levels reflect the amount of stored body fat. Leptin is a negative feedback signal that acts on the hypothalamus to alter the expression of several neuroendocrine peptides that regulate energy intake and expenditure. Central resistance to leptin is a prominent feature of obesity.

Increased leptin levels in individuals who are obese are independent of the lipid profile but strongly correlate with the BMI. Leptin exhibits direct effects on monocytes that results in secretion of the interleukin (IL)-1 receptor antagonist (IL-1RA). This cytokine antagonist has anti-inflammatory properties. Although leptin treatment works very well in patients who are leptin-deficient, the use of leptin in patients who are obese and who already have high levels of leptin has shown limited efficacy.



Obesity is a complex, multifactorial chronic disease influenced by the interaction of several factors, such as genetic, endocrine, metabolic, environmental (social and cultural), behavioral, and psychological components. The basic mechanism involves energy intake that exceeds energy output.



The number of overweight individuals in the world has been estimated at 1.7 billion. In the United States, the problem is at epidemic proportions. As much as two thirds of the population in the United States is overweight, and half of the people in this group can be classified as obese.



The Swedish Obese Subjects (SOS) study is an ongoing, prospective study of 2010 obese participants who underwent bariatric surgery and 2037 obese patients who received usual care in the primary health care system. Compared to the control group, obese adults who underwent surgery experienced a reduced number of cardiovascular deaths and a lower incidence of heart attack and stroke. [1, 2]  A 2017 report from the SOS group found that bariatric surgery reduced the long-term incidence of female-specific cancer, particularly endometrial cancer. [3]

Low back pain is a common complaint among obese patients. A retrospective study of morbidly obese patients who underwent bariatric surgery found that patients experienced a significant decrease in low back and radicular pain after surgery, which led to improvements in quality of life. Patients also experienced a marked increase in the L4-5 intervertebral disc height. [4]

An Australian study by Keating et al compared the results of weight-loss treatments in patients who had been diagnosed with type 2 diabetes mellitus in class I/II obesity, estimating the lifetime costs and quality-adjusted life-years (QALYs) for individuals who had undergone surgically induced weight loss and for patients who had utilized conventional weight loss treatment. [5]

In this study, the mean duration of diabetes remission over a lifetime was 11.4 years in the surgical therapy group and 2.1 years in the conventional therapy group. [5] Over the remainder of their lifetime, surgical therapy patients lived 15.7 discounted QALYs, compared with 14.5 discounted QALYs for conventional therapy patients. Mean discounted lifetime costs were AUD $98,900 per surgical therapy patient and AUD $101,400 per conventional therapy patient (AUD $1 = USD $0.74). Compared with conventional therapy, surgical therapy yielded a mean healthcare saving of AUD $2400 and 1.2 additional QALYs per patient.

In another study, Keating et al looked at the within-trial cost efficacy, over 2 years, of surgical treatment relative to that of conventional therapy for achieving remission in patients recently diagnosed with type 2 diabetes mellitus with class I/II obesity. [6]  Trial intervention costs included gastric banding surgery, mitigation of complications, outpatient medical consultations, medical investigations, pathology, weight-loss therapies, and medication.

An incremental cost-effectiveness analysis demonstrated that the mean 2-year intervention costs per patient were Au $13,400 for surgical therapy and Au $3400 for conventional therapy; laparoscopic adjustable gastric band (LAGB) surgery was responsible for 85% of the difference. [6] For surgical patients, outpatient medical consultation costs were threefold greater than those for conventional patients, but medication costs were 1.5 times higher for patients who underwent conventional therapy. The cost differences occurred primarily in the trial's first 6 months. In relation to conventional treatment, the incremental cost-effectiveness ratio for surgical therapy was Au $16,600 per case of diabetes remitted.

An updated Cochrane review from 2014 that included 22 trials with 1798 participants concluded that surgical treatment of obesity yielded greater improvement in weight loss and weight-associated comorbidities than nonsurgical interventions did, regardless of the type of procedure, [7]  though certain procedures were associated with greater weight loss and fewer comorbidities than others.

In this review, Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy had comparable outcomes, and both had better outcomes than adjustable gastric banding. [7]  In very-high-BMI patients, biliopancreatic diversion with duodenal switch yielded better weight loss than RYGB did. Outcomes were comparable for duodenojejunal bypass with sleeve gastrectomy and laparoscopic RYGB. Isolated sleeve gastrectomy led to better weight loss than adjustable gastric banding. Weight-related outcomes were similar for laparoscopic gastric imbrication and laparoscopic sleeve gastrectomy.

In general, with all 22 studies taken into account, rates of adverse events and reoperation were not well reported. [7]  Because the follow-up period in most of the trials reviewed was only 1 or 2 years, the long-term effects of bariatric surgery could not be definitively established.

A study by Jakobsen et al assessed obesity-related comorbidities in 1888 severely obese patients undergoing either bariatric surgery (n = 932; 92 gastric bypass) or specialized medical treatment (n = 956). [8]  Median follow-up was 6.5 years (range, 0.2-10.1 years). Surgical patients were more likely to experience remission and diabetes remission and were less likely to experience new-onset hypertension; however, they also had a greater risk of new-onset depression and treatment with opioids and were more likely to undergo at least one additional GI surgical procedure.

Ikramuddin et al evaluated lifestyle intervention and medical management with (n = 60) and without RYGB (n = 60) for achieving control of type 2 diabetes (composite triple end point: HbA1c < 7.0%, LDL cholesterol < 100 mg/dL, systolic blood pressure < 130 mm Hg). [9]  Of the 120 patients, 98 completed 5-year follow-up. At 5 years, there remained a significantly better composite triple end point in the surgical group; however, the effect size diminished over 5 years, indicating the need for further follow-up to better define the durability of the improvement.