Type 2 diabetes and obesity, both significant contributors to death and disability, are among the most rapidly growing health problems in the world.1,2 Although there have been major advances in the pharmacologic treatment of diabetes, fewer than 10% to 50% of patients achieve the recommended targets for hemoglobin (Hb)A1c or cholesterol levels or blood pressure.2,3 In addition, 85% of patients with type 2 diabetes have a body mass index (BMI) consistent with overweight or obesity, an important cause of insulin resistance.4 However, few individuals with type 2 diabetes and obesity are able to achieve significant, sustained weight loss with diet and lifestyle measures alone.2
Physiologic Mechanisms for Improved Glycemic Control
Bariatric, or metabolic, surgery is usually used for the treatment of severe obesity, but evidence also supports bariatric surgery as an effective treatment for type 2 diabetes in obese patients. Nearly 80% of patients with type 2 diabetes and obesity who undergo bariatric surgery achieve diabetes remission, compared with only 15% of those who achieve remission with intensive pharmaceutical and lifestyle interventions.1
“The mechanism for improved glycemic control and remission of diabetes after bariatric surgery is still unclear due to multiple changes that occur in response to surgery,” Judy Chen, MD, Assistant Professor of General Surgery specializing in bariatric and metabolic surgery at the University of Washington School of Medicine in Seattle, told Endocrinology Advisor.
Dr Chen noted that bariatric surgery appears to induce changes in the gastrointestinal tract and its interactions with the endocrine system in ways that may influence glycemic control. “Bariatric [surgery] alters gastrointestinal motility, nutrient digestion, absorption, gut peptides, bile acids, and gut microflora. The gastrointestinal tract bypass procedures alter the metabolic response to meal ingestion by inducing an earlier rise in blood glucose-lowering hormones such as glucagon-like peptide 1, oxyntomodulin, [peptide] YY and adiponectin. Insulin is decreased, although meal-induced secretion can be increased. In addition, there seems to be a marked improvement in beta cell function and insulin sensitivity,” she said.
According to Florencia Halperin, MD, Co-Director of the Center for Weight Management and Metabolic Surgery at Brigham and Women’s Hospital and Chief of Endocrinology at Brigham and Women’s Faulkner Hospital in Boston, these hormone-related changes after bariatric surgery appear to take place even before weight loss has occurred. “In general, surgery causes blood sugars to rise as part of the stress hyperglycemic response. But patients with type 2 diabetes experience a rapid improvement in their blood sugars after bariatric surgery. Oftentimes they are able to come off insulin before going home after the surgery,” she said.
However, Dr Halperin pointed out that not all bariatric procedures have the same effect on glycemic control. “Gastric banding does not seem to induce physiologic differences, and the improvement in diabetes observed seems to be more related to weight loss. On the other hand, we believe that gastric bypass and sleeve gastrectomy, which are more commonly performed than the lap band, do change physiology in a way that promotes improvement of blood sugars in type 2 diabetes.”
Bariatric Surgery and Long-Term Diabetes Complications
Bariatric surgery may normalize blood glucose levels, but whether it reduces the risk for long-term microvascular and macrovascular complications from diabetes remains an unanswered question. According to Dr Halperin, the longest follow-up period published to date is only 5 years for randomized trials comparing surgical treatment with medication intervention for weight loss and diabetes. “That is not long enough to have good answers on macrovascular complications,” she said. “We don’t yet have randomized trials that tell us about cardiovascular mortality, for example, in the longer term.”
Designing a new randomized trial to compare the effects of bariatric surgery with those of medical management on long-term diabetes complications may not be feasible, Dr Halperin said. Because bariatric surgery has been shown to be more effective for treating type 2 diabetes than pharmacologic and lifestyle interventions at 5 years, such a trial might lack clinical equipoise. Therefore, randomized trials that were previously conducted to evaluate bariatric surgery vs medical management for type 2 diabetes are continuing to follow up with participants in an attempt to determine the impact of surgery on long-term diabetes complications.
“Some of the studies that we have to shed light on these questions are longer in duration, but they were not randomized trials,” Dr Halperin added. These nonrandomized studies, however, may help us understand whether bariatric surgery lowers the incidence of cardiovascular risk factors. An observational prospective study recently published in the New England Journal of Medicine found that patients with type 2 diabetes who underwent Roux-en-Y gastric bypass (n=418) had lower rates of hypertension and dyslipidemia at 12 years compared with those who did not have the surgery (n=417).5