Using medical records data, researchers with  the National Patient-Centered Clinical Research Network (PCORnet) Bariatric Study analyzed the five-year outcomes for more than 46,000 adults who underwent bariatric surgery (also called metabolic or weight-loss surgery). A subset of these adults had type 2 diabetes, and a separate analysis was conducted to determine the effectiveness of two types of surgery, sleeve gastrectomy and gastric bypass, for this group. Here, David Arterburn, MD, MPH, describes the study findings and discusses bariatric surgery guidelines for patients with type 2 diabetes.

Q: What were the PCORnet Bariatric Study’s findings for people who have type 2 diabetes?

A: The good news is that the cumulative rates of diabetes remission during the five years after surgery are quite similar between the two procedures. The difference was 86.1 percent of patients achieving remission within 5 years of gastric bypass, compared with 83.5 percent for sleeve gastrectomy. We define diabetes remission as hemoglobin A1C that is less than 6.5 percent, the standard cut point for diagnosing diabetes, after being off diabetes medications for at least three months.

The not-so-good news is that the rate of relapse from diabetes remission within five years for patients who received sleeve gastrectomy was higher, at 41.6 percent, compared with the rate of relapse for gastric bypass patients, at 33.1 percent. If patients either restart their medication or have a hemoglobin A1C over 6.5, we say they’ve relapsed.

Also, at five years, the hemoglobin A1C levels were lower in the gastric bypass patients, suggesting better glycemic control, than in the sleeve gastrectomy patients. It was half a percentage point difference, which is pretty large on the hemoglobin A1C scale. We know that good glycemic control is associated with reduced risk of having microvascular disease events and may also prevent macrovascular disease events. And so, it may be that the gastric bypass patients in the long term have fewer of those events than the sleeve gastrectomy patients. This study didn’t look at that question, but it suggests that there is an advantage for patients with type 2 diabetes to have the gastric bypass procedure.

Weight loss may factor into the equation for some patients. In the full study, at five years, gastric bypass was associated with a greater average weight loss (56 pounds) than sleeve gastrectomy (41 pounds).

Q: How do the two procedures compare for safety?

A: We published a paper that finds clear differences on the safety side, but in the opposite direction. Patients who underwent a sleeve gastrectomy had fewer return visits to the hospital for reoperation or any hospitalization through five years of follow-up. The rate of reoperation or intervention that happens after the first procedure was 8.9 percent for sleeve gastrectomy patients and 12.3 percent for gastric bypass patients. The margin of difference in the rate of hospitalizations was even larger. At five years, it was 32.8 percent for the sleeve gastrectomy patients and 38.3 percent for the gastric bypass patients.

In terms of the risk of dying from the procedure, bariatric surgery is extremely safe, akin to having gallbladder surgery, which is a very commonly performed procedure. In our study, the 30-day risk of dying from the procedure was 0.2 percent for gastric bypass and 0.1 percent for sleeve gastrectomy. Over the last 20 to 30 years, the techniques for doing bariatric surgery have advanced greatly. In addition, we’re doing a better job of selecting patients for these kinds of procedures who can do well with them.

Q: How do patients with type 2 diabetes who are considering bariatric surgery decide between these two procedures?

A: We’ve done some work to translate these findings into patient decision aids, which are educational tools to help patients talk about benefits and risks with their surgeon and come to an informed choice. There’s no one right choice for every patient. It really comes down to what’s most important to the patient. [Note: Dr. Arterburn reviews benefits and risks in the short video, Helping Patients Choose between Weight Loss Surgery Options.]

Q: For which category of patients with type 2 diabetes is bariatric surgery recommended?

A: The current, most widely used guidelines say if you have type 2 diabetes that’s not well-controlled on medical therapy, and you have a body mass index (BMI) that’s greater than or equal to 35, you are eligible for bariatric surgery.

Randomized studies have compared gastric bypass or sleeve gastrectomy against best available medical care, including diet and exercise, intensive lifestyle treatment, and medical therapy. They have found that patients do better when they get bariatric surgery. Their glycemic control is better and their chance of remission from diabetes is quite a bit better, and that’s even in the group of patients whose BMI is between 30 and 35.

 The American Diabetes Association, the American Society for Metabolic and Bariatric Surgery, and other international organizations support recommendations suggesting that the criteria for bariatric surgery be expanded to include patients who have diabetes with a BMI as low as 30. It may actually be even safer for these patients, because they don’t have quite as severe obesity, and therefore their risk of complications from the procedure appears to be at least as good or better as for people with greater obesity. It also may be that patients do better, in terms of a more durable remission of their diabetes and a lower risk of micro- and macrovascular disease, if we intervene earlier in terms of their obesity and diabetes. Insurance hasn’t quite caught up yet, but I’m hoping that as the evidence continues to mount, that we'll see an expansion in the eligibility for these procedures.

Q: What age range is suitable for bariatric surgery?

A: The PCORnet Bariatric Study included patients up to age 80, and the over-65 population seem to do just as well in terms of weight loss, diabetes outcomes, and risk of complications. They lost slightly less weight overall, but gastric bypass and sleeve gastrectomy performed the same in that regard. The older population has more general operative risk, but they aren’t at substantially greater risk from gastric bypass or sleeve gastrectomy than the younger-aged population.

We don’t have as many studies in adolescents but, given the chronic progressive nature of type 2 diabetes, lifetime risk of developing complications from type 2 diabetes is pretty great. If you’re an adolescent who already has severe obesity and you’re developing diabetes, it seems like a very reasonable thing for you and your doctor and parents to discuss bariatric surgery.

Q: How challenging are the lifestyle changes required after bariatric surgery?

A: A good part of the decision aid tool we developed focuses on life after surgery in terms of diet, exercise, and life-long follow-up requirements. Many patients report that within one to two years after their procedure, some of the same food-related issues they had before surgery begin to emerge again, in terms of cravings or emotionally related eating. Having good psychological support can be very helpful to patients in the long term.

Q: How much weight do patients lose through bariatric surgery?

A: Most patients are maintaining the weight they’ve lost. The average weight loss at five years was 25.5 percent of their weight at surgery for gastric bypass patients and 18.8 percent for sleeve gastrectomy patients. Average weight loss at five years is slightly lower for patients who have type 2 diabetes, 24.1 percent, and 16.1 percent, respectively.

We did a separate study of teens, age 12 to 18 years, who had severe obesity. It wasn’t focused just on patients with type 2 diabetes, but we saw that patients in this study had similar weight loss as the adults. In fact, in the adolescents, sleeve gastrectomy seemed to do even better than it did with the adults. It was closer to gastric bypass in terms of its effect on weight loss at least through three years of follow-up.

We hear anecdotal stories about patients who regain all their weight, but it’s actually relatively uncommon for this to happen. Within five years, less than 5 percent of gastric bypass patients and less than 12 percent of sleeve gastrectomy patients regain weight to within 5 percent of where they started. The average patient maintains a substantial weight loss, which of course is what’s responsible in large part to the improvement in their diabetes.

Q: The PCORnet Bariatric Study was observational and not a clinical trial. Why is this important?

A: The cohort for our study was drawn from medical records databases, so the data is from patients and providers going about their usual care. There could be differences between patients who choose gastric bypass and patients who choose sleeve gastrectomy. That’s why randomized trials are generally considered the gold standard. Although we used advanced statistical techniques to try to balance all the measurable factors between the two groups—like age, sex, race, ethnicity, hemoglobin A1C at the time of surgery, and severity of diabetes—there’s still the potential that there are other reasons why patients were having differences in their outcomes that aren’t related to the procedure itself.

The randomized trials generally show that when you take patients with diabetes and you randomly assign them to either gastric bypass or sleeve gastrectomy, the differences in the rates of remission and hemoglobin A1C improvement are smaller than what we found in the PCORnet Study. But what’s interesting about our real-world data, is it shows that the gastric bypass patients do better in routine clinical practice. We don’t exactly know why that is.

Our next line of research is to begin to develop better, individualized prediction models and incorporate that information into those decision aids that I was talking about. The individualized model would provide patients with specific predictions, based on their personal characteristics, about their chance of durable remission or relapse of their diabetes, developing micro- or macrovascular disease from their diabetes, dying over time, expected weight loss, and risk of having a reoperation or a rehospitalization.

How do you present information on weight-loss surgery to your patients with type 2 diabetes? Tell us below in the comments.