Has Research Optimized the Targeted Use of Weight Loss Surgery for Glucose Control?

For the foreseeable future, weight loss surgery is here to stay as a preferred medical treatment for obesity. Bariatric surgery is often described as a therapy of last resort, reserved only for those at the most extreme levels of obesity who have failed previous therapies. However, some are advocating expansion of the clinical indications for weight loss surgery to include more people with chronic diseases that respond favorably to surgically induced weight loss and lower thresholds of baseline body weight.

This is seemingly welcome news in the sense that surgery is the most effective obesity therapy currently available. Weight loss surgery patients can expect to lose roughly one-third of their preoperative body weight during the first postoperative year,¹ and roughly two-thirds of patients can expect to maintain this weight loss during several years. Perhaps more importantly, at least from a disease-management perspective, several articles from a recent issue of the New England Journal of Medicine (NEJM) found that weight loss surgery was superior to standard medical treatment for type 2 diabetes.^2,3 One of these studies² found that, compared to the standard treatment group, the proportion of participants with normalized blood glucose after 1 year was nearly four times higher in the group that had weight loss surgery.

Despite these encouraging trial findings, it seems premature to view weight loss surgery as a strong public health strategy to combat obesity or type 2 diabetes. It does not prevent new obesity cases, and it requires more intensive medical care, sometimes secondary to major complications, that can increase short-term health care costs.

The NEJM studies were not considered “game changers” from a scientific perspective because of their relatively small sample sizes.⁴ But they likely made major inroads into the psyche of acceptability among the swelling ranks of U.S. adults suffering from the often doggedly inseparable comorbidities of persistent obesity and uncontrolled type 2 diabetes. As weight loss surgery starts to seem like a more acceptable, routine therapeutic option to this fast-growing segment of the U.S. adult population (and to their medical providers), more weight loss surgeries will be demanded and may become “the new normal” among those with type 2 diabetes and obesity and perhaps even among those with modest levels of excess body weight.

But there remain significant gaps in the literature on this topic that should give the medical and scientific communities pause before embracing this prognostication. The National Institutes of Health has recognized such research limitations and recently funded several large studies on the differential effectiveness of various weight loss surgery procedures on glucose control. This is undoubtedly a step in the right direction, but it remains to be seen whether these new studies will yield enough knowledge to justify changing clinical practice guidelines.

It seems tempting to overlook the progressive biological decrement in β-cell functioning that characterizes type 2 diabetes and usually requires more aggressive therapies as afflicted individuals age. Some researchers have suggested that clinicians often mistakenly leave patients with the impression that sustained weight loss is all this is needed to avoid antidiabetic medications and essentially arrest metabolic disease processes.⁵

But previous research seems to suggest that stark improvements in glucose control for a given weight loss tend to be greatest for those with highly elevated baseline blood glucose levels and even then only in the short term. These improvements usually erode over time, even among those who maintain their weight loss.^6–8 A recent study found that diabetes recurrence or significant worsening of glucose control over 3 years occurred in 24% of weight loss surgery patients with type 2 diabetes who initially experienced successful diabetes resolution or significant improvement in glucose control.⁹ This trend was most pronounced in those at the lowest levels of preoperative BMI and those who regained the most weight.

The term “remission” is often used to describe the impact that weight loss surgery can have on type 2 diabetes. But what happens throughout many years or decades to the predictable metabolic patterns outlined above is largely unknown.

Perhaps the most crucial, but least understood, contributor to long-term surgical success points to the social-cognitive conditions that support sustained low-calorie eating and regular physical activity. At the end of the day, weight loss surgery works because it imposes strong bodily consequences on the amount and types of food people choose to eat (recognizing the additional contribution of nutritional malabsorption for some procedures).

Relatively little is known about how to prevent some weight loss surgery patients from 1) failing to adhere to the postoperative nutrition recommendations, 2) regaining weight, and 3) experiencing diabetes recurrence. In other words, weight loss surgery does not seem to directly alter the powerful environmental contingencies or resolve underlying emotional coping issues that encourage or maintain overeating for some individuals. The degree to which these behavioral phenomena operate similarly and can be modified in weight loss surgery patients with type 2 diabetes needs further exploration because the medical and economic consequences of surgical failures will arguably be most severe in this group.

Given the high stakes of weight loss surgery in general and for individuals with type 2 diabetes in particular, clinicians hope to learn more about the relative advantages and disadvantages of the various types of available procedures and their effects on long-term glycemic control. What subgroups of type 2 diabetes patients have the highest probability of success with each type of procedure? Which have the highest probability of failure? Why? Given the medical complexities of this population, are there additional barriers to sustained lifestyle changes not yet observed or that are particularly challenging to modify in typical home/work/leisure environments?

The widespread but targeted application of weight loss surgery for glucose control may eventually be shown to improve the American public's health, but there seems to be much room still for optimization. A conservative approach is urged on this front before more methodologically rigorous studies can confirm that weight loss surgery results in clear, consistent, and lasting glucose-control benefits and improved quality of life above and beyond standard medical therapies for individuals with type 2 diabetes.

• American Diabetes Association(R) Inc., 2012