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Bariatric surgery

Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Weight loss surgery article more useful, or one of our other health articles.

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What is bariatric surgery?

Bariatric surgical procedures are an option for treating severe obesity, by reducing intake or absorption of calories. There are various options, all of which have potential complications.

A 2014 Cochrane review concluded that surgery results in greater improvement in weight loss outcomes and weight-associated comorbidities compared with non-surgical interventions, regardless of the type of procedures used.1

One meta-analysis at 10 or more years and a single-centre study of laparoscopic adjustable gastric banding with 20 years of follow-up found that all current procedures are associated with substantial and durable weight loss.2

One randomised controlled trial found that, among obese participants with type 2 diabetes, bariatric surgery with two years of an adjunctive low-level lifestyle intervention resulted in more disease remission than did lifestyle intervention alone.3

Bariatric surgery should always be performed in a specialist centre and long-term follow-up of patients is necessary.

For more general information regarding obesity and its management, see the separate articles Obesity in Adults and Obesity in Children.

Who is considered for bariatric surgery?4

Bariatric surgery is an option in severely obese patients, where lifestyle and medication have been evaluated but found not to be effective. Surgery can be combined with other treatments. Referrals are usually made via a specialised obesity management service.

There are clear guidelines from the National Institute for Health and Care Excellence (NICE) about who should be considered for bariatric surgery:


  • BMI ≥40 kg/m2 OR BMI 35-40 kg/m2 with other significant disease (eg, type 2 diabetes, hypertension) that could be improved by weight loss and:

    • All appropriate non-surgical measures have failed to achieve or maintain adequate clinically beneficial weight loss.

    • They are receiving or will receive intensive specialist management.

    • They are generally fit for anaesthesia and surgery.

    • They commit to the need for long-term follow-up.

  • Bariatric surgery is the option of choice (instead of lifestyle interventions or drug treatment) for adults with a BMI of more than 50 kg/m2 when other interventions have not been effective.

  • For people with recent onset (within the previous ten years) type 2 diabetes mellitus:

    • If BMI ≥35 kg/m2, expedite assessment for bariatric surgery (as long as they will receive assessment in a specialist tier 3 service.)

    • Consider assessment for bariatric surgery in a tier 3 service if BMI is 30-34.9 kg/m2.

    • For those of Asian origin, consider assessment for bariatric surgery in a tier 3 service at lower BMI than other populations.

Young people

Surgery is not generally recommended, as it is fraught with ethical issues and the potential long-term benefits and complications are not yet known.5

NICE suggests that it may be considered in exceptional circumstances, if:

  • They have achieved or nearly achieved physiological maturity.

  • They are receiving or will receive intensive specialist management. This will include:

    • Full information on procedures available and risks and benefits.

    • Management of comorbidities.

    • Psychological support before and after surgery.

    • Regular postoperative assessment, including specialist dietetic and surgical follow-up

    • Information about access to plastic surgery, such as apronectomy, where appropriate.

    • Access to suitable equipment for obese young people.

    • Assessment of fitness for anaesthesia and surgery.

  • They have had a comprehensive psychological, educational, family and social assessment before undergoing bariatric surgery.

  • They have had a full medical evaluation, including genetic screening or assessment before surgery to exclude rare, treatable causes of obesity. They should also have had a specialist assessment to exclude eating disorders.

Editor's note

Dr Krishna Vakharia, 28th July 2023

Obesity: identification, assessment and management4

NICE has updated its guidance on referral for bariatric surgery for at risk groups.

They advise to consider:

A referral for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background using a lower BMI threshold - 37.5 or 32.5 and 37.5 with a health condition such as cardiovascular disease, hypertension, idiopathic intracranial hypertension, non-alcoholic fatty liver disease with or without steatohepatitis, obstructive sleep apnoea or Type 2 diabetes.

An expedited referral for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background using a lower BMI threshold - BMI 27.5 to 32.5 - who have recent-onset (diagnosed within the past 10 years) type 2 diabetes.

Orlistat may be used to maintain or reduce weight before surgery for people who have been recommended surgery as a first-line option, if it is considered that the waiting time for surgery is excessive.

There are increasing demands for bariatric surgery to be considered as a valid option in children and adolescents in the face of the increasing prevalence of obesity in this age group.6

Some research suggests that it may also be worthwhile for those with a BMI of 30-35.7 Few procedures are performed on the elderly but the risk is thought to be no higher than any other gastrointestinal procedure.8 The risk:benefit ratio for those with a BMI >70 is currently being researched but one study of 49 patients reported that it was a safe procedure.9

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Contra-indications and cautions10 11

  • Unfit for surgery.

  • Uncontrolled alcohol or drug dependency.

  • Uncontrolled emotional disorders.

  • Lack of ability to understand surgery, consequences, need for follow-up.

  • Some centres advise pre-operative psychiatric and nutritionist assessment.

Types of procedure for bariatric surgery12 13

  • Procedures are classified as restrictive, malabsorptive or both.

    • Restrictive procedures produce a feeling of fullness with lower food intake.

    • Malabsorptive procedures limit calorie uptake from the intestine.

    • It may be that these methods of action overlap, and that the effect is physiological, via endocrine and neuronal means, rather than purely limiting calorie intake.

  • There are various procedures and variations on them, and these have evolved over a period of 50 years. The vast majority are now performed with a minimally invasive or laparoscopic approach.

Bariatric surgery procedures currently used

  • Restrictive:

    • Laparoscopic adjustable gastric banding.

    • Vertical sleeve gastrectomy.

  • Malabsorptive:

    • Biliopancreatic diversion with/without duodenal switch.

  • Both restrictive and malabsorptive:

    • Roux-en-Y gastric bypass (RYGB).

    • Other types of gastric bypass.

  • Other procedures:

    • Gastric stimulation.

    • Intragastric balloon.

Choice of procedure4

Bariatric surgery should be performed by a specialised team in a tertiary centre. The choice of procedure is partly determined by local expertise; it is important that all operations be performed by an experienced surgeon in a specialised multidisciplinary unit. Factors to take into account are:

  • Fitness for surgery.

  • Degree of obesity.

  • Goals.

  • Comorbidities.

  • Best available evidence about effectiveness and long-term effects.

  • Facilities available, and experience of surgeon.

  • Some centres have a two-stage approach, using a restrictive procedure initially, followed by a malabsorptive procedure later if necessary.

The use of the laparoscopic sleeve gastrectomy has increased in recent years.14 The most commonly used procedures in the UK currently are laparoscopic adjustable gastric banding, sleeve gastrectomy and gastric bypass.15

Many studies and meta-analyses have tried to make comparisons between available procedures. The Cochrane review of 2014 concluded that outcomes were similar between RYGB and sleeve gastrectomy, and both of these procedures had better outcomes than adjustable gastric banding.1

In those with very high BMI, biliopancreatic diversion with duodenal switch were found to result in greater weight loss than RYGB. It was noted that across all studies adverse event rates and re-operation rates were generally poorly reported, and the long-term effects of surgery remain unclear.

Explanation of bariatric procedures

  • Laparoscopic adjustable gastric banding: places a constricting ring around the stomach, below the gastro-oesphageal junction. The bands incorporate an inflatable balloon which can adjust the size of the ring, to regulate food intake.

  • Sleeve gastrectomy: most of the stomach is removed, leaving a sleeve-shaped cylinder of stomach with reduced capacity. This procedure is irreversible.

  • Gastric bypass: creates a small gastric pouch (restrictive) joined to the jejunum, bypassing the duodenum and proximal jejunum (malabsorptive). The RYGB is the usual procedure at the current time.

  • Biliopancreatic diversion: is a more extensive form of the gastric bypass, with the gastric pouch joined to the ileum, totally bypassing the duodenum and jejunum. It produces more extreme malabsorption.

  • Duodenal switch: biliopancreatic diversion is sometimes performed with a duodenal switch. This produces a short distal length of small intestine, severely limiting caloric absorption. This is a complex operation which takes some hours to complete.

  • Gastric stimulation: uses an implanted pacemaker-type device to produce electrical gastric stimulation, thought to cause a feeling of satiety.

  • Intragastric balloon: this is an endoscopic rather than surgical procedure, placing a silicone balloon inflated in the stomach to promote a feeling of satiety. There is insufficient evidence to assess its effectiveness and there have been complications such as gastric erosions and ulcers. It is therefore usually removed after six months.

  • Endoscopic techniques: apart from balloon insertion, various other endoscopic procedures are being developed but are not currently in common NHS use. These are collectively known as primary obesity surgery endolumenal (POSE).16

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Those who have had bariatric surgery should be followed up by the specialist bariatric service for a minimum of two years. This should include:

  • Monitoring nutritional intake (including protein and vitamins) and mineral deficiencies.

  • Dietary and nutritional advice and support.17

  • Physical activity advice and support.

  • Psychological support.

  • Monitoring for comorbidities.

  • Medication review.

  • Information about professionally led or peer-led support groups. For example, the British Obesity Surgery Patients Association (BOSPA).13

After discharge from bariatric surgery service follow-up, ensure that all people are offered at least annual monitoring of nutritional status and appropriate supplementation according to need.

Benefits of bariatric surgery procedures18

  • Weight loss. In a long-term Swedish trial, weight loss averaged 18% after 20 years.

  • Remission of diabetes mellitus. The Swedish trial showed a 72% remission rate two years after surgery.

  • The Swedish study also reported a reduction in overall mortality of 29%, and a reduction in the incidence of myocardial infarction, stroke and cancer.

  • Evidence suggests that non-alcoholic fatty liver disease (including steatosis, steatohepatitis and fibrosis) appears to improve or completely resolve in the majority of patients after bariatric surgery-induced weight loss.19

Complications and disadvantages of surgery12

Pre-operative discussion is important; patients may have unrealistic ideas about the amount of weight they are likely to lose, the need for follow-up and the potential complications.20 Data from 3.6 million patients have shown an overall pooled perioperative mortality of 0.08%.21

The incidence of complications within the first six months varies from 4-25%, and depends on procedure used, duration of follow-up and individual patient characteristics. Complications to consider include:

  • Peri-operative complications as for any abdominal surgery include venous thromboembolism. The use of prophylaxis has reduced the incidence of deep vein thrombosis and pulmonary embolism considerably.22

  • Possible complications of banding are band slippage, leakage, infection or migration.23

  • Surgical complications of bypass surgery include leakage or stenosis of the stoma, gastrointestinal ulcers or bleeding, small bowel obstruction and hernias.

  • Nausea and vomiting may occur due to overeating or to stenosis at the surgery site.

  • Dumping syndrome: symptoms are flushing, light-headedness, palpitations, fatigue and diarrhoea, typically triggered by sugar after a RYGB. It is a neurohormonal reaction. It may help to discourage overeating.

  • Malnutrition: micronutrient deficiencies are a recognised problem, especially with malabsorptive procedures. Iron-deficiency anaemia is the most common complication. Calcium, zinc, folate and vitamin D deficiencies can occur. Thiamine, B12 and copper deficiencies may cause neurological symptoms and should be remembered. Protein-calorie malnutrition can also occur. Long-term follow-up is important.

  • Gallstones can develop as a consequence of rapid weight loss.24

  • Hyperoxaluria which can be mitigated to some extent by aggressive fluid intake, oral calcium and citrate supplementation.

  • Inadequate weight loss and weight regain. The latter is affected by behavioural patterns that can be assessed pre-operatively in order to identify individuals particularly at risk.25

  • Up to 35% may require revisional procedures, particularly in gastric banding.

  • Bariatric surgery patients show a higher suicide rate than the general population.26

  • Removal of excess skin after significant weight loss may not be available on the NHS.

The National Confidential Enquiry into Patient Outcome and Death (NCEPOD) report

The NCEPOD report on bariatric surgery was published in 2012. In order to reduce mortality and morbidity associated with bariatric surgery, the following initiatives were suggested:15

  • Surgeons should undergo a minimum number of procedures before being allowed to operate unsupervised.

  • Service provision should be restricted to a number of accredited centres with a set minimum number of procedures per annum.

  • All patients must have access to the full range of specialised professionals appropriate for their needs in line with NICE guidelines.

  • Psychological support should be initiated at an earlier stage in the process.

  • Consent should be a two-stage process and should not be taken on the day of surgery.

  • A clear discharge plan should be provided to the GP as soon as possible, including detailed dietary advice.

  • Postoperative psychological advice should be made available if required.

Further reading and references

  1. Colquitt JL, Pickett K, Loveman E, et al; Surgery for weight loss in adults. Cochrane Database Syst Rev. 2014 Aug 8;8:CD003641. doi: 10.1002/14651858.CD003641.pub4.
  2. O'Brien PE, Hindle A, Brennan L, et al; Long-Term Outcomes After Bariatric Surgery: a Systematic Review and Meta-analysis of Weight Loss at 10 or More Years for All Bariatric Procedures and a Single-Centre Review of 20-Year Outcomes After Adjustable Gastric Banding. Obes Surg. 2019 Jan;29(1):3-14. doi: 10.1007/s11695-018-3525-0.
  3. Courcoulas AP, Belle SH, Neiberg RH, et al; Three-Year Outcomes of Bariatric Surgery vs Lifestyle Intervention for Type 2 Diabetes Mellitus Treatment: A Randomized Clinical Trial. JAMA Surg. 2015 Oct;150(10):931-40. doi: 10.1001/jamasurg.2015.1534.
  4. Obesity: identification, assessment and management; NICE Clinical guideline, November 2014 - last updated July 2023
  5. Caniano DA; Ethical issues in pediatric bariatric surgery. Semin Pediatr Surg. 2009 Aug;18(3):186-192.
  6. Hsia DS, Fallon SC, Brandt ML; Adolescent bariatric surgery. Arch Pediatr Adolesc Med. 2012 Aug;166(8):757-66. doi: 10.1001/archpediatrics.2012.1011.
  7. Picot J, Jones J, Colquitt JL, et al; Weight loss surgery for mild to moderate obesity: a systematic review and economic evaluation. Obes Surg. 2012 Sep;22(9):1496-506. doi: 10.1007/s11695-012-0679-z.
  8. Varela JE, Wilson SE, Nguyen NT; Outcomes of bariatric surgery in the elderly. Am Surg. 2006 Oct;72(10):865-9.
  9. Eldar SM, Heneghan HM, Brethauer SA, et al; Laparoscopic bariatric surgery for those with body mass index of 70-125 kg/m2. Surg Obes Relat Dis. 2012 Nov-Dec;8(6):736-40. doi: 10.1016/j.soard.2011.09.024. Epub 2011 Oct 14.
  10. Guidelines for Clinical Application of Laparoscopic Bariatric Surgery; Society of American Gastrointestinal and Endoscopic Surgeons, 2008
  11. Pories WJ; Bariatric surgery: risks and rewards. J Clin Endocrinol Metab. 2008 Nov;93(11 Suppl 1):S89-96. doi: 10.1210/jc.2008-1641.
  12. Arterburn DE, Courcoulas AP; Bariatric surgery for obesity and metabolic conditions in adults. BMJ. 2014 Aug 27;349:g3961. doi: 10.1136/bmj.g3961.
  13. BOSPA - British Obesity Surgery Patient Association
  14. Nguyen NT, Nguyen B, Gebhart A, et al; Changes in the makeup of bariatric surgery: a national increase in use of laparoscopic sleeve gastrectomy. J Am Coll Surg. 2013 Feb;216(2):252-7. doi: 10.1016/j.jamcollsurg.2012.10.003. Epub 2012 Nov 21.
  15. Too Lean a Service?; National Confidential Enquiry into Patient Outcome and Death, 2012
  16. Familiari P, Boskoski I, Marchese M, et al; Endoscopic treatment of obesity. Expert Rev Gastroenterol Hepatol. 2011 Dec;5(6):689-701. doi: 10.1586/egh.11.77.
  17. GP Guidance: Management of nutrition following bariatric surgery; The British Obesity and Metabolic Surgery Society, Aug 2014
  18. Sjostrom L; Review of the key results from the Swedish Obese Subjects (SOS) trial - a prospective controlled intervention study of bariatric surgery. J Intern Med. 2013 Mar;273(3):219-34. doi: 10.1111/joim.12012. Epub 2013 Feb 8.
  19. Tai CM, Huang CK, Hwang JC, et al; Improvement of nonalcoholic fatty liver disease after bariatric surgery in morbidly obese Chinese patients. Obes Surg. 2012 Jul;22(7):1016-21. doi: 10.1007/s11695-011-0579-7.
  20. Kim JH, Wolfe B; Bariatric/metabolic surgery: short- and long-term safety. Curr Atheroscler Rep. 2012 Dec;14(6):597-605. doi: 10.1007/s11883-012-0287-3.
  21. Huppler L, Robertson AG, Wiggins T, et al; How safe bariatric surgery is-An update on perioperative mortality for clinicians and patients. Clin Obes. 2022 Jun;12(3):e12515. doi: 10.1111/cob.12515. Epub 2022 Mar 9.
  22. Stroh C, Birk D, Flade-Kuthe R, et al; Evidence of thromboembolism prophylaxis in bariatric surgery-results of a quality assurance trial in bariatric surgery in Germany from 2005 to 2007 and review of the literature. Obes Surg. 2009 Jul;19(7):928-36. doi: 10.1007/s11695-009-9838-2. Epub 2009 May 5.
  23. Eid I, Birch DW, Sharma AM, et al; Complications associated with adjustable gastric banding for morbid obesity: a surgeon's guides. Can J Surg. 2011 Feb;54(1):61-6.
  24. Desbeaux A, Hec F, Andrieux S, et al; Risk of biliary complications in bariatric surgery. J Visc Surg. 2010 Aug;147(4):e217-20. doi: 10.1016/j.jviscsurg.2010.08.001.
  25. Odom J, Zalesin KC, Washington TL, et al; Behavioral Predictors of Weight Regain after Bariatric Surgery. Obes Surg. 2009 Jun 25.
  26. Peterhansel C, Petroff D, Klinitzke G, et al; Risk of completed suicide after bariatric surgery: a systematic review. Obes Rev. 2013 Jan 9. doi: 10.1111/obr.12014.

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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