Metabolic surgery and lower BMI – does it make the cut?

Excess adiposity (obesity) and type 2 diabetes are closely linked. Increasing weight is associated with increased diabetes risk, while weight loss reduces diabetes risk. Bariatric surgery has the most durable effect on weight loss and has a significant effect on glycaemic control (Leong and Taheri, 2012). Early guidelines advocated bariatric surgery for those with BMI of ≥35 kg/m² and associated comorbidities, such as type 2 diabetes. This recommendation, in combination with limitations in the availability of bariatric surgery, resulted in the most complex patients receiving bariatric surgery procedures.

Evidence has emerged that older age, longer diabetes duration, poor diabetes control and insulin treatment reduce the potential of diabetes remission post-bariatric surgery. Simultaneously, Purnell and colleagues (summarised on following page) have provided a greater appreciation of the metabolic effects of bariatric surgery that are independent of weight loss. The above observations have resulted in the renaming of bariatric surgery as “metabolic” surgery and, increasingly, there are recommendations to provide this surgery to those with BMIs less than 35 kg/m² (Rubino et al, 2016).

Cummings and Cohen (summarised on following page) write in support of metabolic surgery for those with diabetes and lower BMI than the traditional recommendations. While they make a compelling case for this indication for bariatric surgery, most of the studies they refer to have included a small number of patients, and there are no long-term data regarding sustained improvements in diabetes, quality of life and mortality. Also, generally, the medical interventions employed in surgical trials have not used the full range of medical treatment options available for treatment of obesity and diabetes.

Ikramuddin and colleagues (summarised alongside) examined the impact of bariatric surgery on diabetes in those with BMI range of 30–39.9 kg/m², by enrolling 120 patients and randomising them in a multicentre clinical trial to lifestyle intervention alone or lifestyle intervention plus laparoscopic gastric bypass operation. They examined target improvements in HbA_1c (<53 mmol/mol [7%]), dyslipidaemia (LDL-cholesterol <2.59 mmol/L [100 mg/dL]) and blood pressure (systolic blood pressure <130 mmHg).

At 12 months, 19% of the lifestyle group achieved the targets set for the three parameters compared to 47% of those who received gastric bypass. At 36 months, these percentages had diminished to 9% and 28% for lifestyle intervention and gastric bypass, respectively. In the lifestyle intervention, 22% achieved an HbA_1c <53 mmol/mol (7.0%) at 36 months compared to 58% in the gastric bypass group. At 36 months, 14% of the gastric bypass group achieved the triple end-point without medication compared to 2% in the lifestyle intervention alone group. The gastric bypass group experienced double the number of serious or clinically significant adverse events (51 events) compared to the lifestyle group (24 events).

It should also be noted that while, as expected, the lifestyle group achieved outcomes with more medications compared to the gastric bypass group, the gastric bypass group needed to take additional vitamin replacements.

The findings from this study point out some of the unanswered questions regarding metabolic surgery for those with diabetes and lower BMI: the available studies include few participants, there are few long-term studies, surgery may not be as effective as suggested, the side effects and complications of surgery appear to be under-estimated, and cost-effectiveness remains to be established.

To read the article summaries, please download the PDF