Gastric bypass surgery and the importance of long follow-up times

At the New York Times Well blog, Anahad O'Connor writes about a new study, published in the journal Obesity Surgery, is a caution against recent optimism about gastric bypass surgery's ability to combat Type 2 diabetes. David E. Arterburn and his coauthors conducted a retrospective cohort study of 4,434 adults with Type 2 diabetes who underwent gastric bypass surgery between 1995 and 2008. Within five years after surgery, 68.2% of the subjects experienced "an initial complete diabetes remission" -- but then 35.1% of those "remitters" redeveloped diabetes within another five years.

The study subjects all received Roux-en-Y gastric byass (RYGB) procedures and were enrolled in one of three US integrated healthcare delivery systems (HealthPartners (of Minnesota), Kaiser Permanente Northern California, and Kaiser Permanente Southern California). All had Type 2 diabetes, either uncontrolled or controlled by medication, prior to surgery, and had had the disease for an average of 4.5 years. The majority of the subjects (77%) were women, with an average age of 49.6. Investigators looked for both partial and complete remission of diabetes, based on fasting glucose and/or HbA1c levels 90 or more days after medication discontinuation, measured by the end of the last filled prescription for diabetes medication. They note that their cutpoint for HbA1c signaling complete remission (<6.0%) was lower than those used by academic bariatric centers, which have reported higher percentages of Type 2 diabetes remission following gastric bypass surgery.

The authors report that 37.1% of subjects achieved complete remission one year after surgery; that percentage grew to 63.3% at three years, and 68.2% at five years. Complete remission was less likely among women, those with poor preoperative glycemic control, those who were treated with insulin or oral hypoglycemic agents before surgery, and those who had been diabetic for longer prior to surgery.

The authors followed the 2,254 subjects who'd experienced complete post-surgery diabetes remission and found that 7.9% had relapsed within one year, 22.1% within three years, and 35.1% within five years. Subjects at higher risk of relapse were those who were older at the time of surgery, had poor preoperative glycemic control, used insulin prior to surgery, and had diabetes for longer.

BMI data were available for 2,116 of the subjects (thanks to an electronic records system implemented from 2005-2008), and the researchers conducted analyses of this subpopulation. They report, "We found that the pre-operative BMI values were not significantly different (p=0.93) between the 1,224 cases who never completely remitted their diabetes (BMI 45.5 kg/m²), 103 cases who completely remitted but relapsed (BMI 45.8 kg/m²), and 789 cases who durably remitted their diabetes (BMI 45.6 kg/m²)." However, the subpopulation subjects those who remitted their diabetes lost slightly more weight and regained less of it over time than their non-remitting counterparts.

In their Discussion section, the authors write:

The results presented here shed new light on the importance of preoperative patient selection and counseling when one of the goals of surgical intervention is durable diabetes remission. We consistently found that those treated with insulin were less likely to remit and more likely to relapse than those not on insulin prior to surgery. ... these data suggest that when the main goal of surgical treatment is durable diabetes remission, earlier surgical intervention is likely to be more effective.

... Patients should be counseled that bariatric surgery alone does not reliably “cure” diabetes. However, the remission rates achieved by RYGB appear to be far better than what could be achieved by any other behavioral or drug treatment.

The authors also note that bariatric surgery might have other benefits, short of diabetes remission, for patients with more advanced diabetes, and that this is one area for further study.

This finding will likely complicate decisiomaking for patients and their doctors. Obese patients who've recently been diagnosed with diabetes are probably advised to try lifestyle interventions and medications initially, and it can take years of repeated attempts at healthier exercise and eating behaviors before people sustainably adopt these habits. But if longer diabetes duration and poorer glycemic control make surgery less likely to result in sustained diabetes remission, patients may not want to spend years trying less-invasive treatments. On the other hand, patients who've had poorly controlled diabetes for many years may be less eager to pursue surgery if they know that any resulting diabetes remission has a good chance of reversing.

Even for those who aren't grappling with decisions about diabetes treatment, this study is a good reminder that it's important to measure intervention outcomes for several years post-intervention. (Having electronic medical records for large groups of patients who've stayed in the same healthcare system for several years helps.) Studies with long follow-up times can be difficult and expensive to conduct, but they're essential for informing patients' treatment decisions.