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Review Article

Bariatric surgery and type 2 diabetes

Stewart, Jennifer PA-C; Allen, Sarah PA-C; Weidman-Evans, Emily PharmD, BC-ADM

Author Information
Journal of the American Academy of Physician Assistants: January 2020 - Volume 33 - Issue 1 - p 28-32
doi: 10.1097/01.JAA.0000615484.77430.1b
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Obesity is a prominent disease worldwide, affecting 35% of adults living in the United States, and nearly 500 million (6.5%) adults worldwide.1 Although an inactive lifestyle and excessive intake of calories is often thought to be the main link to obesity, multiple factors contribute.2,3 Associated risk factors include endocrine, behavioral, cultural, genetic, metabolic, and social components.2,3 One theory of genetic risk suggests increased amounts of leptin hormone produced by adipocytes in the presence of hypothalamus resistance leads to the disruption of energy regulation.2 Obesity is associated with the development of type 2 diabetes as well as hypertension, heart disease, osteoarthritis, and stroke.

Due to the strong link between obesity and type 2 diabetes, weight-loss programs involving diet and exercise, pharmacotherapy, and patients' willingness to take control of their disease are the primary tools that healthcare providers use in type 2 diabetes management. However, management becomes complicated when patients do not achieve healthful blood glucose levels despite lifestyle modifications and adherence to therapy with multiple medications. The risk of developing or worsening damage to the cardiovascular system, kidneys, or other organs increases as hyperglycemia continues.

Bariatric surgery is largely known for its role as a weight loss tool but is gaining notoriety as a successful treatment for patients with refractory type 2 diabetes. When medications and changes to lifestyle such as diet and exercise fail to improve disease status, bariatric surgery has been used to significantly gain control of obesity, type 2 diabetes, and other comorbidities as well as reduce costs, cardiovascular complications, and death.1,2 By altering components of the gastrointestinal (GI) tract, bariatric surgery helps patients reduce food intake, feel full sooner, or reduce absorption of ingested food components. Patients' blood glucose levels fall and they need fewer medications to treat diabetes. Additionally, cardiovascular risk factors and comorbidities such as hypertension and hyperlipidemia may be improved. To improve long-term success rates after bariatric surgery, patients with diabetes are expected to follow a postoperative diet for their lifetime.

Box 1
Box 1

As bariatric surgery gains more prominence in diabetes, clinicians must understand these procedures, which patients are appropriate candidates, and how to manage patients postoperatively. Clinicians also must assess the expectations of surgical candidates and their willingness to follow a permanent postoperative diet in addition to making sure the procedure will provide a safe and effective long-term outcome.1,2 However, the benefits of bariatric surgery hold great potential for managing type 2 diabetes. Specifically, bariatric surgery in patients with diabetes has shown improved beta-cell function and reduction of BP, lipid levels, and weight.4


The jejunoileal bypass performed in 1954 by Linner and Kremen was the first successful bariatric surgery performed in the United States.2 However, the resulting malabsorption (which allowed the weight loss) also led to poorly tolerated deficiencies in patient vitamin intake, excessive growth of intestinal bacteria, and drastic stool changes, prompting procedure reversal and cessation of this procedure.

Currently, the more common surgeries involve gastric restriction combined with mild malabsorption by Roux-en-Y gastric bypass, reduction of contents entering the stomach with laparoscopic sleeve gastrectomy, or laparoscopic adjustable gastric banding (Table 1).

Comparison of three bariatric surgeries2,12,19

Although complications and adverse reactions are reported with all of these procedures, the more popular restrictive-only procedures are much more tolerable. About 200,000 bariatric surgeries are performed annually in the United States.5 As obesity is one of the greatest risk factors for type 2 diabetes, bariatric surgery has become a well-regarded therapy to induce remission in patients with diabetes.1


Excessive adipose tissue leads to a decrease in adipokines and adiponectin that regulate insulin action.6 Adipose tissue may distribute across the body differently among patients with the same body mass index (BMI); a waist-to-hip ratio may be determined and represent central obesity that concentrates around the viscera versus general obesity that is distributed to other areas such as the thigh.7 Regardless of tissue distribution, BMI is the measurement for bariatric surgery candidacy.4 Although obese adults without comorbidities must have a BMI of 40 or more to be considered surgical candidates, consider bariatric surgery in patients with diabetes who have a BMI of 35 or greater after treatment failure with lifestyle changes and pharmacologic regimens.1,8,9 This often is determined by A1C of at least 7% or more in patients on multiple antidiabetes medications and lifestyle changes for more than 1 year.8

Obtain a detailed patient history to help assess risk factors and other undiagnosed comorbidities that may affect the necessity for or outcome of bariatric surgery.3 Patients with comorbidities such as cardiovascular disease or obstructive sleep apnea may need an echocardiogram or a sleep study, respectively.1 Obesity, cardiovascular disease, and decreased pulmonary function may affect the effectiveness of general anesthesia, perioperative management, and postoperative recovery.1 If surgery is not contraindicated in these patients, they may need to postpone surgery until these conditions are improved or corrected.1

Assess patient motivation to ensure that patients will be successful with the lifestyle changes required after surgery.1,10 Patients with a lack of impulse control and unhealthful eating behavior may be less successful in postoperative weight loss.10 Patients who are unable to follow the postoperative course for nutrition and medical management also are at increased risk for complications and poor results after surgery.1 A nutritionist can educate patients before and after surgery about the adjustments of nutritional status. Patients should undergo psychologic evaluation before surgery to assess behavioral and cognitive health and determine if their expectations of the surgery are reasonable. Patients should consult with the surgeon to determine the risks, benefits, and most effective surgical option.3

Husted and colleagues attempted to improve success rates of bariatric surgery by addressing the psychologic component of patient eating behavior.11 The method was to increase patient awareness of their financial investment in the surgery and the personal and physical results following surgery in order to deter poor decision-making. Increasing a patient's awareness as part of the treatment yielded results that showed an increased average weight loss of 6.77 kg (15 lb) in the group receiving surgical intervention compared with 0.85 kg (1.9 lb) among control group participants.


Bariatric surgery has proven beneficial in lowering patient weight, A1C, and blood glucose levels. A meta-analysis of 11 randomized-controlled trials (925 subjects) compared the three most common procedures in relation to weight loss and found that laparoscopic sleeve gastrectomy resulted in the largest change in BMI and excess weight lost, followed by Roux-en-Y bypass, then laparoscopic adjustable band gastrectomy (Table 1).12 Laparoscopic adjustable band gastrectomy resulted in fewer complications than the other two procedures.

Since 2011, bariatric surgery has been included as part of the American Diabetes Association's management strategy for patients with obesity and type 2 diabetes.13 Some, but not all, bariatric procedures appear to be more effective than traditional pharmacologic and lifestyle interventions in controlling diabetes. A 2015 study that compared laparoscopic adjustable band gastrectomy with intensive medical and weight management did not show any statistically significant difference in change in A1C between these two methods, although weight loss after 12 months was greater with surgery.14

However, a 2013 study by Ikramuddin and colleagues compared results in 120 participants who had either Roux-en-Y bypass, antidiabetes medication, and lifestyle changes or only medication and lifestyle changes.5 An A1C below 7% was achieved in 49% of the patients who had surgery, compared with 19% of the traditional intervention group. In addition, overall, patients who had surgery required fewer medications (3 versus 4.8) and lost a significantly greater portion of their body weight (26.1% versus 7.9%) compared with the traditional intervention group. Patients who had surgery also reported a decrease in other obesity-related issues such as low back pain, death due to cardiovascular events, and stroke. The 2-year follow-up related to this study reported significantly more infections and nutritional deficiencies in the surgical group, leading to the authors' conclusion that benefits and risks must be weighed.15

Another study comparing surgery (Roux-en-Y or laparoscopic sleeve gastrectomy) to intensive medical therapy in 150 patients showed similar results.16 Five percent of those receiving only medical therapy achieved an A1C of less than 6%, compared with 28.6% of patients who had Roux-en-Y bypass and 23.4% of those who had laparoscopic sleeve gastrectomy (P < .05).16 Patients who had bariatric surgery also experienced a greater reduction in body weight (23% for Roux-en-Y and 19% for laparoscopic sleeve gastrectomy) compared with patients who had medical therapy (5%).16 Patients in the surgery group also had greater reductions in triglycerides and insulin use and increases in both high-density lipoprotein cholesterol and quality-of-life scores. More patients in the surgical group experienced anemia, although no specific nutritional deficiencies were noted (16% in medical therapy versus 38% in surgical group; P < .05); those in the medical therapy group experienced more hypoglycemic episodes (91% versus 62%, P < .05) and excessive weight gain (19% versus 0, P < .05).16

A meta-analysis of 33 studies (1,375 patients) compared Roux-en-Y bypass and laparoscopic sleeve gastrectomy to determine if one surgery was superior to the other in controlling diabetes.17 No statistically significant difference was found between the two surgeries in terms of diabetes remission (defined by individual studies, but most often an A1C of less than 6.5% or 6%, with a reduction or discontinuation of medications) at 3 or 12 months postoperative. Similarly, the differences in weight loss at 3 and 12 months were not statistically significant. The meta-analysis did not compare adverse reactions to the two procedures.


The overall risk of postoperative death after Roux-en-Y bypass or laparoscopic sleeve gastrectomy is less than 0.5%.2 Patients with a history of hypertension, myocardial infarction, bleeding disorders, stroke, or more severe ranges of BMI are at increased risk for postoperative complications such as malabsorption or nutritional deficiencies, surgical site infection, gastroesophageal reflux, and gastrointestinal obstruction.12

Careful and frequent monitoring after bariatric surgery for patients with diabetes is crucial given the potentially rapid improvement in blood glucose levels. Clinicians must anticipate this dramatic change in order to prevent hypoglycemia and other possible adverse reactions.18 Medications that increase insulin secretion, such as sulfonylureas and meglitinides, are discontinued at the time of surgery to prevent hypoglycemia. Due to GI adverse reactions, alpha glucosidase inhibitors also are stopped. Although incretin-based medications such as GLP-1 analogs and DPP-4 inhibitors may theoretically be safe to continue, they often are discontinued because of the GI adverse reactions and risk of hypoglycemia. Metformin often is continued postoperatively depending on the patient's renal function; the medication can eventually be discontinued depending on the patient's therapeutic response to surgery. Insulin dosing often is substantially reduced and close monitoring is strongly recommended to determine appropriate future dosing. Educate patients to closely monitor their blood glucose levels regardless of their medication regimen.

Fat malabsorption, most common in patients after Roux-en-Y bypass, may lead to nutritional deficiencies of fat-soluble vitamins such as A, D, E, and K, or lead to diarrhea and foul-smelling flatulence. Inadequate amounts of iron, calcium, and protein also may be absorbed, leading to the need for supplementation.

The Roux-en-Y procedure has been linked to postoperative anastomotic leak and pulmonary embolism. The most common late complication is stomal stenosis. Another common complication is dumping syndrome, in which the food contents are introduced into the small intestine too rapidly, causing tachycardia, diaphoresis, vomiting, and low blood glucose levels.19,20 Dumping syndrome is uncommon in restrictive procedures such as laparoscopic sleeve gastrectomy or laparoscopic adjustable band gastrectomy.

Food intolerance is consistently common as an early and late complication of both laparoscopic sleeve gastrectomy and laparoscopic adjustable band gastrectomy. A study by Kalarchian and colleagues compared self-reported GI adverse reactions after laparoscopic adjustable band gastrectomy and Roux-en-Y bypass and found vomiting to be common in both groups.20 Plugging of the smaller opening to the stomach caused by rapid eating or not chewing well was reported more frequently in patients who had had laparoscopic adjustable band gastrectomy. Educating patients before surgery about potential postoperative complications may help them prevent or manage these complications better.

Before surgery, also educate patients about postoperative nutritional requirements, because nutritional deficiencies and eating habits may complicate the postoperative experience.20 Tell patients to increase their intake of water and lean protein and to reduce intake of processed snack foods, carbonated beverages, and caffeine.19 Patients should take supplemental iron, vitamin B12, folate, calcium, and vitamin B for the rest of their lives.2 Some patients may need higher-than-recommended daily calcium; in one study, patients who had Roux-en-Y bypass experienced increased bone turnover and low intestinal calcium absorption after surgery.21


Bariatric surgery has proven to be a successful treatment option for patients with obesity and diabetes who have failed the routine medical regimen of lifestyle modification and antidiabetes medication. Patients who are good candidates for surgery go on to achieve better control of their blood glucose levels, reduce the amount of medications they may need, and improve other comorbidities such as hypertension, obesity, and hyperlipidemia. These benefits, however, must be balanced with the potential for risks such as nutritional deficiencies and infections. Current data suggest that laparoscopic sleeve gastrectomy is as effective as Roux-en-Y bypass for diabetes control and has fewer complications, making it a desirable procedure. Based on the current data, bariatric surgery should be considered a viable option for patients with obesity and diabetes.


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type 2 diabetes; bariatric surgery; weight loss; obesity; blood glucose; remission

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