Bariatric surgery for type 2 diabetes: Weighing the impact for obese patients
ABSTRACTObesity is a potent risk factor for the development and progression of type 2 diabetes, and weight loss is a key component of diabetes management. Bariatric surgery results in significant weight loss and remission of diabetes in most patients. After surgery, glycemic control is restored by a combination of enforced caloric restriction, enhanced insulin sensitivity, and increased insulin secretion.
KEY POINTS
- After Roux-en-Y gastric bypass and biliopancreatic diversion, normoglycemia is restored within days, even before the patient has lost much weight.
- Alterations in postprandial levels of intestine-derived hormones (glucagon-like peptide 1, peptide YY, and ghrelin) contribute to the robust metabolic benefits of intestinal bypass procedures.
- Nutritional deficiencies are common after bariatric surgery, and long-term follow-up is mandatory for surveillance of metabolic status.
- Although curing diabetes cannot yet be considered a goal of bariatric surgery, it may be a serendipitous benefit.
Observational studies of the effect of Roux-en-Y surgery on diabetes
Several observational studies have evaluated the benefit of Roux-en-Y surgery for patients with type 2 diabetes mellitus.
Pories et al15 followed 608 severely obese patients, of whom 165 (27%) had type 2 diabetes or impaired glucose tolerance.
At a mean follow-up of 7.6 years after surgery, 83% of the diabetic patients were off their antidiabetic drugs, and 99% of those with impaired glucose tolerance were normoglycemic, with normal fasting glucose and hemoglobin A1c levels. Marked improvements in hyperlipidemia, hypertension, fertility, osteoarthritis, and obstructive sleep apnea were also noted.
Schauer et al17 observed similar results in 1,160 morbidly obese patients, of whom 240 (21%) had type 2 diabetes or impaired fasting glucose.
After laparoscopic Roux-en-Y gastric bypass surgery, fasting glucose and hemoglobin A1c levels returned to normal levels in 83% of cases and were markedly improved in the remaining 17%. Significantly (80%) fewer patients needed oral antidiabetic agents or insulin (79% fewer). Patients most likely to achieve complete remission of diabetes were those with the shortest duration of diabetes (< 5 years), the mildest severity of diabetes (diet-controlled), and the greatest weight loss after surgery. The rate of diabetes remission in patients who had been diabetic for 5 years or less was 95%, compared with 75% in those who had been diabetic for 6 to 10 years and 54% in those who had been diabetic for more than 10 years (P < .001).
The Swedish Obese Subjects (SOS) study18 prospectively followed 1,703 patients, of whom 118 had type 2 diabetes, for 10 years after various bariatric surgery procedures (primarily vertical gastroplasty). In a control group that received medical therapy, 77 patients had type 2 diabetes. Medical therapy was ill-defined with respect to aggressiveness and adherence to intervention with lifestyle and pharmacotherapy.
At 2 years, the surgical group had lost a mean of 28 kg, glycemic control had improved in the diabetic patients, and many of them had been able to stop taking oral hypoglycemic drugs or insulin. In contrast, the need for these agents increased in the medically treated patients. The proportion treated by diet alone rose from 59% to 73% in the surgical group, but declined from 55% to 34% in the nonsurgical group.13
In these studies, surgery also reduced the risk of progressing from impaired glucose tolerance to type 2 diabetes; the risk was 30 times lower in the study by Pories et al.15 In the SOS study,18 the frequency of diabetes was 30 times lower at 2 years and five times lower at 8 years after surgery.
Studies of biliopancreatic diversion
Data on the effects of biliopancreatic diversion, a primarily malabsorptive procedure, are limited to European studies.
Scopinaro et al19,20 reported long-term follow-up data on 312 patients with type 2 diabetes who underwent biliopancreatic diversion; 310 patients (99%) achieved normal fasting glucose values by 1 year after surgery. At 10 years after surgery, 98% of the patients were still in complete remission of diabetes, defined as normal glucose values without the use of antidiabetic medications.
Others have noted similar findings.21,22
Limitations of the studies
Although these data seem encouraging, these studies had major limitations.
The patients were mostly white women with severe obesity, ie, a BMI greater than 40 kg/m2, which is not representative of patients with type 2 diabetes in the community. Only about 20% had glucose intolerance or overt type 2 diabetes mellitus. Would other groups benefit, particularly men and those with lesssevere obesity?
Moreover, these studies were observational, with no randomized control groups. Many reports consisted of large case series. It is not clear how specific bariatric procedures were chosen or what criteria were used for performing bariatric surgery. A lack of complete follow-up data is also a concern.
Needed are large randomized trials evaluating the effects of various bariatric procedures in a less obese cohort with type 2 diabetes, ie, typical patients seen in the community. Moreover, surgery has not been compared directly with more vigorous medical weight-loss strategies, such as those used in the Diabetes Prevention Project6 and the Look AHEAD trial.7,8
A randomized controlled trial of gastric banding
The only randomized controlled trial to date that compared standard medical diabetes therapy with bariatric surgery was conducted by Dixon et al.14
Sixty patients with type 2 diabetes (duration < 2 years and mean hemoglobin A1c 7.7%) were randomized either to receive medical management as defined by the American Diabetes Association guidelines or to undergo laparoscopic adjustable gastric banding.
At 2 years, the rate of remission (defined as hemoglobin A1c < 6.2% and a normal fasting glucose level) was 13% in the medical treatment group vs 73% in the surgery group (P < .001). Patients receiving medical treatment had lost a mean of 1.7% of their body weight, vs 20.7% in the surgical patients (P < .001). Weight loss was strongly associated with remission of type 2 diabetes after surgery.
This study was controversial in that the medical intervention in this trial was not as aggressive as in the Diabetes Prevention Project and Look AHEAD trials.
INDICATIONS FOR BARIATRIC SURGERY IN PATIENTS WITH DIABETES
According to guidelines from the National Institutes of Health,23 the current indications for bariatric surgery include a BMI of 40 kg/m2 or higher, or a BMI between 35 and 40 kg/m2 with at least two obesity-related comorbidities. Diabetes is considered a key comorbidity that justifies the risk of surgery. The guidelines suggest that bariatric surgery be discussed with all severely obese patients (BMI > 35 kg/m2) with type 2 diabetes who have not been able to lose weight with other weight-control approaches.
Since type 2 diabetes mellitus is a progressive disease characterized by relentless deterioration of beta-cell function, many endocrinologists favor aggressive weight-loss approaches early in the course of the disease. We believe that bariatric surgery should be considered early, as it may help preserve pancreatic betacell function and slow the progression of microvascular and macrovascular complications.
