Two Steps Ahead? Bariatric Surgery for Prevention of Type 2 Diabetes

Published - Written by Rena Xu

Imagine you’re trying to convince a severely obese middle-aged man to lose weight.  You recite a litany of morbid conditions associated with obesity; prominent on the list is Type 2 diabetes (T2D). “But I don’t have diabetes,” the patient counters. “What would weight loss do for me?”

For patients like him, you explain, losing weight can help prevent diabetes from developing in the first place. Previous studies have shown a reduced incidence of T2D with behavioral or pharmacologic treatment of obesity.  Now, there is evidence that bariatric surgery may also be effective for diabetes prevention.

A prospective case-matched intervention study by Carlsson et al., published in this week’s NEJM, compared the long-term effects of bariatric surgery to usual care on the incidence of T2D. The study enrolled patients between September 1987 and January 2001 and included 1658 bariatric surgery patients and 1771 matched controls. All patients were markedly obese (with a body mass index, or BMI, of at least 34 kg/m2 in men and 38 kg/m2 in women) but did not have diabetes at baseline.  Patients were followed for up to 15 years.

At 10 years, the average weight loss among patients in the intervention arm was approximately 20 kg (44 lbs). In contrast, the average weight loss among patients in the control arm never exceeded 3 kg (6.6 lbs).

As compared to usual care, bariatric surgery was associated with a much lower rate of developing T2D – 392 patients in the control arm and 110 patients in the intervention arm developed T2D, corresponding to incidence rates of 28.4 per 1000 person-years and 6.8 per 1000 person-years, respectively (P<0.001). The adjusted hazard ratio for the relative treatment effect of surgery versus usual care was 0.17 (0.13-0.21, P<0.001).

In a subgroup analysis, all types of bariatric surgery received by patients in the study group – banding, vertical banded gastroplasty, and gastric bypass – were associated with reduced T2D incidence. The study was not statistically powered to detect outcome differences between types of surgery. Patients’ baseline BMI did not predict T2D incidence or the preventive effect of surgery.

In addition to its apparent benefits, surgery carried considerable risks – 14.7% of patients in the intervention arm experienced some form of complication, including three patients who died and 46 (2.8%) who required reoperation within 90 days of surgery. Notably, almost 90% of the operations in the study were performed using open surgery. In contrast, most bariatric procedures today are performed using laparoscopic technique, which is generally associated with lower complication rates.

Do these findings make bariatric surgery a more compelling treatment option for patients with severe obesity? In a corresponding editorial, Dr. Danny Jacobs of Duke University School of Medicine cautions against drawing such conclusions – at least for now. He writes: “[I]t remains impractical and unjustified to contemplate the performance of bariatric surgery in the millions of eligible obese adults. […] The current study should provide an impetus to develop a more complete understanding of the mechanisms by which the various bariatric procedures exert their beneficial effects. Such understanding will be important because it will enable the identification of the persons who are the most appropriate candidates for surgery.”

Perhaps what this study shows most clearly is the need for a clearer picture of what causes T2D and how exactly bariatric surgery confers its observed health benefits.

As for your skeptical patient, these findings may make the case for weight loss all the more compelling – in addition to mitigating existing health problems, addressing his obesity could help him bypass other issues altogether.

How does bariatric surgery fit into your current treatment algorithm for patients with severe obesity? Do you manage diabetic versus non-diabetic patients with obesity differently? Will the results of this study affect how you counsel your patients with obesity about their treatment options?