Bariatric Surgery

Clare J. Lee, M.D., MHS


  • A frequently done, effective surgical intervention for obese individuals to reduce weight and improve obesity-related comorbidities such as diabetes. Results in weight loss by restriction of overall nutrient intake, malabsorption of nutrients, and/or a combination of restriction and malabsorption.

The two most commonly performed bariatric surgery procedures in the U.S. are the following:

  • Laparoscopic sleeve gastrectomy: restrictive procedure that removes large portion of the greater curvature of the stomach leaving a stomach "sleeve" along the lesser curvature. Can be done as the first part of a duodenal switch or as a standalone procedure.
  • Roux-en-Y gastric bypass: combination restrictive and malabsorptive procedure that creates a small gastric pouch by separating the proximal and distal stomach; the proximal gastric pouch is anastamosed to a loop of jejunum ("Roux limb"), while the bypassed distal stomach and proximal small bowel ("Y limb") is anastamosed distally to the jejunum.

Less commonly performed bariatric surgery procedures are the following:

  • Laparoscopic adjustable gastric band: restrictive procedure that inserts a band around the proximal stomach; the band is connected to a subcutaneous port used to adjust the amount of gastric restriction provided by the band.
  • Biliopancreatic diversion (BPD) with or without duodenal switch: combination restrictive and malabsorptive procedure that creates a laparoscopic sleeve gastrectomy with remaining stomach either: (1) attached to lower portion of smaller intestine (BPD); or (2) attached to upper small intestine with creation of separate biliary loop, both of which connect to common channel of lower smaller intestine (duodenal switch).


  • Up to 44% of all patients diagnosed with diabetes are obese[17][15].
  • Of an estimated 225,000 bariatric surgeries performed per annum, 15- 30% have diabetes[15].
  • Bariatric surgery, especially Roux-en-Y gastric bypass, can result in the resolution of type 2 diabetes in nearly 30% at up to 5 years after surgery [4].
  • Diabetes-related microvascular and macrovascular complications, mortality and all-cause mortality are significantly decreased after gastric bypass[6][3].


  • According to the American Diabetes Association, metabolic surgery should be recommended to treat type 2 diabetes in patients with class III obesity (BMI ≥40 kg/m2) and in those with class II obesity (BMI 35.0–39.9 kg/m2) when hyperglycemia is inadequately controlled by lifestyle and optimal medical therapy.[1]
  • Surgery should also be considered for patients with type 2 diabetes and BMI 30.0–34.9 kg/m2 if hyperglycemia is inadequately controlled despite optimal treatment with either oral or injectable medications.[1]
  • These BMI thresholds should be reduced by 2.5 kg/m2 for Asian patients.
  • Specific coverage guidelines vary by insurance carrier (e.g. documentation of a failed trial of diet and exercise and performance of surgery at an American Society for Bariatric Surgery designated Center of Excellence).


Glycemic control in immediate post-operative period (days 0-3)

Patients with preexisting type 1 diabetes

  • Both the basal and bolus insulin doses should be lowered since the overall insulin requirement may decrease substantially and rapidly after bariatric surgery.
  • Patients should be reminded to continue their basal insulin post-operatively even when the oral intake is small in order to avoid diabetic ketoacidosis.

Patients with preexisting insulin-requiring type 2 diabetes

  • Prior to bariatric surgery, providers should consider checking the plasma C-peptide to gauge the patient’s endogenous insulin production given the rising prevalence of obesity among adults with both type 1 and type 2 diabetes [2].
  • If C-peptide is low or not detectable, insulin should be continued post operatively similar to in type 1 diabetes.
  • Insulin-requiring patients often require significantly lower doses of insulin and oral hypoglycemic agents post-operatively due to decreased oral intake and rapid improvement in hepatic insulin resistance.

Patients with preexisting type 2 diabetes on oral glucose-lowering agents

  • With Roux-en-Y or sleeve gastrectomy procedures, hyperglycemia may improve dramatically within several days, well before significant weight loss.
  • Oral intake is advanced according to institution- or provider-specific protocols. Most diets begin with clear liquids and advance to full liquids or pureed foods that are high in protein, and low in fat and carbohydrates.
  • A combination of basal and rapid-acting prandial insulin is preferred to keep fasting blood glucose levels between 80 and 110 mg/dl and post-prandial glucose levels below 180 mg/dl.
  • Some patients best treated with meal-time insulin only during this time period due to irregular intake and decreasing insulin requirements.
  • Doses of oral agents should be withheld in non-insulin requiring patients. Specifically, secretagogues should be discontinued in the immediate post-operative period.

Glycemic control in the outpatient setting

  • Oral intake is advanced further from full liquids and pureed foods ultimately to a regular diet (small, frequent meals) consisting of high-protein, low-fat and low-carbohydrate meals.
  • In patients with type 2 diabetes, hemoglobin A1C should be checked 3 months after the surgery and periodically thereafter as clinically indicated [1].
  • While many patients go on to needing less or no diabetes medication in the first post-operative year, periodic screening for hyperglycemia is needed to adjust diabetes medications as needed during the subsequent years.

Micronutrient deficiencies

  • Post-bariatric surgery patients are at risk for a variety of micronutrient deficiencies including: B12, iron, calcium, vitamin D, folate, B1 and others.
  • All patients receiving bariatric surgery should be started on multivitamins containing iron, calcium citrate and vitamin D after bariatric surgery.
  • Patients should be monitored regularly for micronutrient deficiencies. The frequency depends on the type of surgery. Patients undergoing laparoscopic adjustable band should be monitored annually, and gastric bypass and bilopancreatic diversion patients require monitoring every 3-6 months.
  • Although calcium is absorbed throughout the small intestine and colon, calcium containing foods (e.g. milk, cheese) may provoke bloating, cramping and diarrhea post-bariatric surgery placing patients at risk for deficiency. Calcium citrate with vitamin D is the recommended form of calcium because of better absorption.
  • Oral B12 often not sufficient to replete B12 deficiencies. B12 should be administered in sublingual, intranasal or intramuscular forms as oral B12 not absorbed well due to anatomical disruption of B12 and intrinsic factor binding following gastric bypass and other malabsorptive surgeries (biliopancreatic diversion/duodenal switch).
  • Iron absorption is impaired following gastric bypass and other malabsorptive surgeries due to bypass of the duodenum (the site of iron absorption). Some patients may require intravenous iron therapy.
  • Folate deficiency may occur as a result of B12 deficiency, impaired intestinal absorption, or inadequate oral intake. Folate supplementation is recommended in patients after bariatric surgery.
  • B1 deficiency can arise in the setting of inadequate oral intake, or impaired intestinal absorption and may result in Wernicke-Korsakoff syndrome. B1 is usually a component of most multivitamin preparations, but deficient individuals can be treated with intramuscular injections.
  • Vitamin D deficiency can result from decreased oral intake, and impaired absorption due to poor mixing of vitamin D with bile salts. Daily oral supplementation is recommended.


  • Medical:
    • Electrolyte abnormalities
    • Dumping syndrome. Early dumping syndrome: rapid onset within 15 minutes. Caused by rapid emptying of food into the small bowel. Key symptoms are vasomotor (hypotension, palpitation, flushing) and gastrointestinal (abdominal cramping, diarrhea, nausea). Late dumping syndrome: delayed onset 1-2 hours after a meal, hyperinsulinemic hypoglycemia is thought to be due to altered gut hormone response (excessive insulin secretion following rapid delivery of glucose into the small intestine, increased GLP-1) and less commonly nesidioblastosis, though the exact mechanism is unknown. Symptoms related to hypoglycemia include extreme hunger, shakiness, nausea, weakness, confusion and in severe cases altered mental status and seizure.[9]
    • Weight regain
    • Gallstones
    • Loose skin after weight loss
    • Laparoscopic adjustable band: vomiting, pain, dysphagia, reflux
  • Surgical:
    • Roux-en-Y gastric bypass or BPD: anastamotic leak, marginal ulceration, stomal stenosis
    • Laparoscopic adjustable band or sleeve gastrectomy: band malfunction (slippage, erosion, infection), leakage, hemorrhage, fistula


  • Follow-up in bariatric surgery patients depends on the comorbidities and the type of surgery performed.
  • Diabetes remission rate appears to be lower in those who are 5 or more years out from bariatric surgery (24% at 6 year follow up in a single center study), likely related to preexisting insulin deficiency, diabetes duration and post-surgical weight regain[8].
  • Hemoglobin A1c monitoring should be continued in the post-operative period.
  • Weight loss depends on the type of operation performed. Expected average weight loss in the first 1-2 years after surgery is 45-85% and 29-87% for Roux-en-Y gastric bypass and laparoscopic adjustable band surgery, respectively.[14]
  • Laparoscopic Roux-en-Y gastric bypass is relatively safe as demonstrated by short-term morbidity and mortality rates comparable to common procedures such as cholecystectomy and appendectomy[7].


  • Bariatric surgery is an effective tool to treat obesity and related comorbidities such as diabetes.
  • Bariatric surgery, especially Roux-en-Y gastric bypass and sleeve gastrectomy, has a profound effect on glucose metabolism, which often leads to improvement in diabetes and in some cases postprandial hypoglycemia.
  • Maintain a high index of suspicion for micronutrient deficiencies.
  • Bariatric surgery is covered by many insurance carriers (e.g. Medicaid) but specific coverage guidelines are carrier-dependent.
  • Bariatric surgery enforces a new relationship to food: patients cannot eat the amount of food they previously consumed.
  • While short-term data on bariatric surgery show significant metabolic improvement and reassuring safety profile, more long-term data are needed to enhance our understanding of long-term safety and efficacy of bariatric surgery.


  1. Kheniser KG, Kashyap SR. Diabetes management before, during, and after bariatric and metabolic surgery. J Diabetes Complications. 2018;32(9):870-875.  [PMID:30042058]
  2. Pilla SJ, Maruthur NM, Schweitzer MA, et al. The Role of Laboratory Testing in Differentiating Type 1 Diabetes from Type 2 Diabetes in Patients Undergoing Bariatric Surgery. Obes Surg. 2018;28(1):25-30.  [PMID:28695457]
  3. Sheng B, Truong K, Spitler H, et al. The Long-Term Effects of Bariatric Surgery on Type 2 Diabetes Remission, Microvascular and Macrovascular Complications, and Mortality: a Systematic Review and Meta-Analysis. Obes Surg. 2017;27(10):2724-2732.  [PMID:28801703]
  4. Schauer PR, Bhatt DL, Kirwan JP, et al. Bariatric Surgery versus Intensive Medical Therapy for Diabetes - 5-Year Outcomes. N Engl J Med. 2017;376(7):641-651.  [PMID:28199805]
  5. Puzziferri N, Roshek TB, Mayo HG, et al. Long-term follow-up after bariatric surgery: a systematic review. JAMA. 2014;312(9):934-42.  [PMID:25182102]
  6. Pok EH, Lee WJ. Gastrointestinal metabolic surgery for the treatment of type 2 diabetes mellitus. World J Gastroenterol. 2014;20(39):14315-14328.  [PMID:25339819]
  7. Aminian A, Brethauer SA, Kirwan JP, et al. How Safe is Metabolic/Diabetes Surgery? Diabetes Obes Metab. 2014.  [PMID:25352176]
  8. Brethauer SA, Aminian A, Romero-Talamás H, et al. Can diabetes be surgically cured? Long-term metabolic effects of bariatric surgery in obese patients with type 2 diabetes mellitus. Ann Surg. 2013;258(4):628-36; discussion 636-7.  [PMID:24018646]
  9. Tack J, Arts J, Caenepeel P, et al. Pathophysiology, diagnosis and management of postoperative dumping syndrome. Nat Rev Gastroenterol Hepatol. 2009;6(10):583-90.  [PMID:19724252]
  10. Mechanick JI, Kushner RF, Sugerman HJ, et al. American Association of Clinical Endocrinologists, The Obesity Society, and American Society for Metabolic & Bariatric Surgery medical guidelines for clinical practice for the perioperative nutritional, metabolic, and nonsurgical support of the bariatric surgery patient. Obesity (Silver Spring). 2009;17 Suppl 1:S1-70, v.  [PMID:19319140]

    Comment: Guidelines published for the perioperative management of bariatric surgery patients.

  11. Dixon JB, O'Brien PE, Playfair J, et al. Adjustable gastric banding and conventional therapy for type 2 diabetes: a randomized controlled trial. JAMA. 2008;299(3):316-23.  [PMID:18212316]

    Comment: Laparoscopic adjustable band surgery is superior to conventional diabetes therapy for the remission of diabetes and weight loss.

  12. Adams TD, Gress RE, Smith SC, et al. Long-term mortality after gastric bypass surgery. N Engl J Med. 2007;357(8):753-61.  [PMID:17715409]

    Comment: Mortality is decreased after gastric bypass surgery.

  13. Service GJ, Thompson GB, Service FJ, et al. Hyperinsulinemic hypoglycemia with nesidioblastosis after gastric-bypass surgery. N Engl J Med. 2005;353(3):249-54.  [PMID:16034010]

    Comment: Nesidioblastosis is an uncommon phenomenon in bariatric surgery patients associated with hyperinsulinemic hypoglycemia.

  14. Buchwald H, Avidor Y, Braunwald E, et al. Bariatric surgery: a systematic review and meta-analysis. JAMA. 2004;292(14):1724-37.  [PMID:15479938]

    Comment: This systematic review reports the efficacy of bariatric surgery for weight loss.

  15. Centers for Disease Control and Prevention (CDC). Prevalence of overweight and obesity among adults with diagnosed diabetes--United States, 1988-1994 and 1999-2002. MMWR Morb Mortal Wkly Rep. 2004;53(45):1066-8.  [PMID:15549021]

    Comment: This article reports the epidemiology of obesity in the diabetic population.

  16. NIH conference. Gastrointestinal surgery for severe obesity. Consensus Development Conference Panel. Ann Intern Med. 1991;115(12):956-61.  [PMID:1952493]

    Comment: NIH consensus panel recommendations that bariatric surgery be considered for carefully selected, morbidly obese patients with acceptable operative risks.

  17. Centers for Disease Control and Prevention. National Diabetes Statistics Report, 2017. Atlanta, GA: Centers for Disease Control and Prevention, U.S. Dept of Health and Human Services; 2017

Last updated: July 4, 2020