Bariatric surgery for people with diabetes and morbid obesity: an evidence-based analysis

In June 2008, the Medical Advisory Secretariat began work on the Diabetes Strategy Evidence Project, an evidence-based review of the literature surrounding strategies for successful management and treatment of diabetes. This project came about when the Health System Strategy Division at the Ministry of Health and Long-Term Care subsequently asked the secretariat to provide an evidentiary platform for the Ministry's newly released Diabetes Strategy.After an initial review of the strategy and consultation with experts, the secretariat identified five key areas in which evidence was needed. Evidence-based analyses have been prepared for each of these five areas: insulin pumps, behavioural interventions, bariatric surgery, home telemonitoring, and community based care. For each area, an economic analysis was completed where appropriate and is described in a separate report.To review these titles within the Diabetes Strategy Evidence series, please visit the Medical Advisory Secretariat Web site, http://www.health.gov.on.ca/english/providers/program/mas/masabout.html,DIABETES STRATEGY EVIDENCE PLATFORM: Summary of Evidence-Based AnalysesContinuous Subcutaneous Insulin Infusion Pumps for Type 1 and Type 2 Adult Diabetics: An Evidence-Based AnalysisBehavioural Interventions for Type 2 Diabetes: An Evidence-Based AnalysisBARIATRIC SURGERY FOR PEOPLE WITH DIABETES AND MORBID OBESITY: An Evidence-Based SummaryCommunity-Based Care for the Management of Type 2 Diabetes: An Evidence-Based AnalysisHome Telemonitoring for Type 2 Diabetes: An Evidence-Based AnalysisApplication of the Ontario Diabetes Economic Model (ODEM) to Determine the Cost-effectiveness and Budget Impact of Selected Type 2 Diabetes Interventions in Ontario

The purpose of this evidence-based analysis was to examine the effectiveness and cost-effectiveness of bariatric surgery for the management of diabetes in morbidly obese people. This report summarized evidence specific to bariatric surgery and the improvement of diabetes from the full evidence-based analysis of bariatric surgery for the treatment of morbid obesity completed by the Medical Advisory Secretariat (MAS) in January 2005. To view the full report, please visit the MAS website at: http://www.health.gov.on.ca/english/providers/program/mas/tech/techmn.html.

CONDITION AND TARGET POPULATION Obesity is defined as an excessive accumulation of body fat as measured by the body mass index (BMI) and calculated as body weight in kilograms (kg) divided by height in metres squared (m(2)). People with a BMI over 30 kg/m(2) are considered obese in most countries. The condition is associated with the development of several diseases, including hypertension, diabetes mellitus (type 2 diabetes), hyperlipidemia, coronary artery disease, obstructive sleep apnea, depression, and cancers of the breast, uterus, prostate, and colon. Clinically severe, or morbid obesity, is commonly defined by a BMI of at least 40 kg/m(2), or a BMI of at least 35 kg/m(2) if there are comorbid conditions such as diabetes, cardiovascular disease, or arthritis. The prevalence of morbid obesity among people with type 2 diabetes has been examined and of 2,460 patients with type 2 diabetes, 52% (n = 1,279) were obese (BMI ≥ 30 kg/m(2)) and 23% (n = 561) had a BMI ≥ 35 kg/m(2). BARIATRIC SURGERY: Men and women with morbid obesity may be eligible for surgical intervention. There are numerous surgical options available, all of which can be divided into two general types, both of which can be performed either as open surgery or laparoscopically: malabsorptive - bypassing parts of the gastrointestinal tract to limit the absorption of food, andrestrictive - decreasing the size of the stomach in order for the patient to feel satiated with a smaller amount foodSurgery for morbid obesity is usually considered a last resort for people who have attempted first-line medical management (e.g. diet, behaviour modification, increased physical activity, and drugs) but who have not lost weight permanently. Surgery is restricted to people with morbid obesity (BMI ≥ 40 kg/m(2)) or those with a BMI of at least 35 kg/m(2) and serious comorbid conditions.

Details of the full literature search can be found in the 2005 evidence-based analysis of bariatric surgery (http://www.health.gov.on.ca/english/providers/program/mas/tech/techmn.html). Briefly, a literature search was conducted examining published works from January 1996 to December 2004, including OVID MEDLINE, MEDLINE In-Process and Other Non-Indexed Citations, EMBASE, the Cumulative Index to Nursing & Allied Health Literature (CINAHL), The Cochrane Library, and the International Agency for Health Technology Assessment/Centre for Review and Dissemination.

Data on the effectiveness or cost-effectiveness of bariatric surgery for the improvement of diabetesSystematic reviews, randomized controlled trials (RCTs), and observational controlled prospective studies that had >100 patientsRandomized controlled trials (RCTs), systematic reviews and meta-analyses

Duplicate publications (superseded by another publication by the same investigator group, with the same objective and data)Non-English-language articlesNon-systematic reviews, letters, and editorialsAnimal and in-vitro studiesCase reports, case seriesStudies that did not examine the outcomes of interest

Improvement or resolution of diabetesThe quality of the studies was examined according to the GRADE Working Group criteria for grading quality of evidence.

There is evidence that bariatric surgery is effective for improvement and resolution of diabetes in patients who are morbidly obese (BMI≥35 kg/m(2)). The quality of evidence for the use of bariatric surgery for the resolution or improvement of diabetes in morbidly obese people, according to the GRADE quality-of-evidence criteria, was found to be moderate (see ES Table 1). Comparison of various bariatric techniques: No prospective, long-term direct comparison is available between malabsorptive and restrictive techniques.Retrospective subgroup analyses from a large observational study showed greater improvement and resolution of diabetes using malabsorptive techniques rather than purely restrictive methods.There is evidence from a meta-analysis that malabsorptive techniques are better than other banding techniques in terms of improvement and resolution of diabetes.

Bariatric surgery, morbid obesity, comorbidity, diabetes ES Table 1:GRADE Quality of Evidence for Bariatric Surgery for the Resolution or Improvement of DiabetesOutcomeQuality AssessmentSummary of FindingsDesignQualityConsistencyDirectnessOtherNo. of PatientsEffectQualityImprovement in HbA1c indiabetic and glucoseintolerant patientsMeta-analysisModerate*ConsistentDirectNonen=171-2.70% (-5.0% to -0.70%)weighted mean change(range)ModerateResolution or improvement of diabetes(Studies reporting combinationas well as studies that only usedthe term "improved", but not thestudies reporting only resolution)Meta-analysisModerate*ConsistentDirectNone414/485(n resolved orimproved/nevaluated)86.0% (78.4% to 93.7%)mean% (95% CI)ModerateResolution of diabetes(diabetes disappeared or nolonger required therapy)Meta-analysisModerate*ConsistentDirectNone1417/1846(n resolved/nevaluated)76.8% (70.7% to 82.9%)mean% (95% CI)ModerateRecovery of diabetes(fasting plasma glucose level ofless than 126 mg per decilitre[7.0 mmol per litre])Observationalprospectivecontrolled studyModerate*ConsistentSomeuncertainty(†)Someuncertainty(‡)control n=84intervention n=1183.45 (1.64 to 7.28)OR (95% CI) at 10 yrsModerate*Downgraded due to study design (not randomized controlled trial)†Unlikely to be an important uncertainty. Inclusion criteria for the SOS study not specific to conventional definition of "morbidly obese" patients (BMI ≥ 40 or ≥ 35 kg/m(2) with comorbid conditions)‡Unlikely to be an important uncertainty. Control group not standardized, however, this lends to the pragmatic nature of the study.