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CTAF supports diabetic surgery for BMI>35 patients

The document supports the use of bariatric surgery to treat type 2 diabetes in the very obese, but could not find sufficient evidence to support its use in less heavy patients.
CTAF cite evidence of long-term health benefits besides weight loss to support decision
Evidence for benefits to patients with BMI under 35 "much less robust"

The California Technology Assessment Forum (CTAF) has published a document assessing the use of bariatric surgery to treat type 2 diabetes, finding evidence of its safety and effectiveness in diabetics with a BMI over 35, but asserting that there is inadequate evidence to recommend its use in diabetics under that weight.

CTAF, an organisation who attempt to identify new health-improving medical technologies through an evidence-based approach, voted unanimously on both findings.

While the forum evaluated evidence for the use of bariatric surgery, including gastric banding, gastric bypass, and sleeve gastrectomy, in the treatment of diabetes, it did not find sufficiently robust evidence to satisfy three of its recommendation criteria in less heavy patients.

“Larger, well designed studies are needed adequately address the important question about the balance of risks and benefits of bariatric surgery in patients with T2DM with a BMI < 35,” says the document.

In deciding whether to recommend the use of a procedure, CTAF specify that it must pass the following criteria: 

  1. The technology must have final approval from the appropriate government regulatory bodies.
  2. The scientific evidence must permit conclusions concerning the effectiveness of the technology regarding health outcomes.
  3. The technology must improve the net health outcomes.
  4. The technology must be as beneficial as any established alternatives.
  5. The improvement must be attainable outside the investigational settings.

The use of bariatric surgery to treat diabetes in patients with BMI over 35 passed all five criteria. However, the authors stated that the evidence base for diabetic surgery in patients with a BMI under 35 was “much less robust”, and that remission of diabetes alone was “not sufficient to counterbalance the significant risks associated with bariatric surgery”, due to the risk of complication and questions over the durability of diabetes remission.

While evidence of the diabetic benefits of patients with BMI over 35 abounded in long-term, large-scale comparative studies like Swedish Obese Subjects and the STAMPEDE study, the authors said that for patients with BMI under 35, the number of studies and length of follow-up was lacking, and there were no randomised trials comparing bariatric surgery in this cohort to medical therapy.

CTAF were not able to find evidence to satisfy criteria three, four or five in support of diabetic surgery for lighter patients.

Regarding upcoming trials that are either proposed or underway, CTAF say: “the majority of the studies are too small and planned follow-up too short to provide definitive answers to the comparative effectiveness of medical versus surgical therapy in less obese patients.” 

However, they note that there is an initiative to standardise measurements and outcomes to enable future researchers to combine results, allowing greater statistical power.

CTAF’s findings are in line with most organisations with positions on the use of bariatric surgery to treat diabetes. 

The UK’s National Institute for Clinical Excellence, who provide national guidelines for medical care, recommend bariatric surgery for patients with a BMI over 40, or over 35 with obesity-related comorbidities. The US’ Centers for Medicare and Medicaid Services cover bariatric surgery for patients with a BMI over 35 and at least one comorbidity, if they have failed to lose weight through other methods of medical intervention.

The CTAF document used evidence from the Swedish Obese Subjects study, in particular, to support diabetic surgery for patients with a BMI over 35. The ongoing study follows 2,010 patients who underwent gastric band, vertical banded gastroplasty, or gastric bypass surgery, matched to 2,037 individuals who did not receive surgery. The patients have so far been followed up for 15-20 years.

Alongside the weight-loss benefits of surgery, diabetic patients in the study saw a 72% remission rate, compared to 21% of the control group. Diabetic symptoms tended to return – at the ten-year point, only 36% were still in remission – but remained significantly lower than the control group.

As well as the diabetic benefits, the surgical cohort had fewer cardiovascular deaths and cardiovascular risk factors, as well as improvements in other obesity-related comorbidities. There was a 29% reduction in all-cause mortality in the surgical group compared to the control group.

While CTAF note that the techniques used in the Swedish Obese Subjects study have now largely been replaced by laparoscopic approaches and new techniques, subsequent observational studies have confirmed that contemporary operations have similar benefits to weight loss, diabetes remission, and drop in medication use.

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