Can bariatric surgery prevent diabetes?
I’ve previously written here about the 2 major New England Journal trials looking at treating type 2 diabetes with bariatric surgery. Those studies showed a very robust ability of bariatric surgery to treat type 2 diabetes. If you can use bariatric surgery to treat type 2 diabetes, what about prevention? This question was examined in a more recent NEJM publication of selected results from the Swedish Obese Subjects (SoS) study from Carlsson et al.
Guest Post by Dr. Jonathan Carter
I’m pleased to say that my friend and colleague, Dr. Jonathan Carter, has agreed to follow this post with a guest blog post of his own, giving his analysis of the study. Dr. Carter is an Assistant Professor of Surgery at UCSF, frequently performing bariatric surgery.
For those who skim blogs…
I’ll start with my take-away points, and then go backwards to analyze the study in more depth. So, without further ado, the major takeaways from this study are:
1) Bariatric surgery impressively reduced the risk of type 2 diabetes in a middle-aged, obese population by 80% compared to the control group. The number needed to treat (NNT) was 1.3!
2) This study did not address the most important comparison, i.e. between bariatric surgery and an intensive lifestyle modification program. Unfortunately, the control group in this study received minimal attempt at lifestyle modification. Prior studies like the Diabetes Prevention Program, the Finnish Diabetes Prevention Study, and the Chinese Diabetes Prevention Study showed between a 30-50% reduction in type 2 diabetes incidence with lifestyle modification. However, one cannot directly compare the rates in these studies to each other.
3) Due to #s 1 and 2 above, the next study should directly compare bariatric surgery and intensive lifestyle modification with regard to diabetes prevention.
4) Weight loss prevents the onset of type 2 diabetes in obese patients. Bariatric surgery causes weight loss.
With these results, we have to start discussing whether it is ethical, reasonable, and cost-effective to use bariatric surgery to prevent type 2 diabetes.
Now, for those of you interested in some more information about the study and results, keep reading…
This study was a prospective, non-randomized trial which enrolled 4,047 obese patients from 1987-2001 in Sweden. The researchers note that they did not randomize the participants due to “ethical reasons related to the high postoperative mortality associated with bariatric surgery in the 1980s.” In other words, enough people died from bariatric surgery at the time the study began that it would have been unethical for them to randomly assign people to have it done.
The control group was selected by a matching algorithm that concurrently tried to keep the current mean values of the matching variables between the two groups as similar as possible. Included patients were aged 37-60 years old and had BMI over 34 for men and over 38 for women. And, of course, they did not have diabetes at baseline. Ultimately, those included in this analysis were 1,658 patients who had surgery and 1,771 who were in the control group.
Baseline characteristics: Surgery group had more severe risk factors
Due to the matching process, those in the surgery group were older, heavier (120 kg vs 114 kg), had higher insulin levels, higher blood pressures, worse cholesterol, higher smoking rates, lower physical activity rates, and higher caloric intakes compared to those in the control group. Because the groups were non-randomized, it was likely that these “sicker” and “riskier” patients were more likely to be recommended surgery by their physicians. However, in the end, this makes the results even more impressive because the surgical group had 80% lower rates of diabetes despite being a sicker group to begin with. The surgical group had the decks stacked against them, and still came out ahead. It is as if the surgical group started a 100 meter race with a 1-2 second handicap, but was still able to win.
No attempt at standardizing lifestyle therapy in control group
As I discussed above, a weakness of this study is that there was no attempt to standardize treatments in the control group. Some might say that this is a positive because it reflects “real-world” treatments. And indeed, the authors note that “patients in the control group received the customary treatment for obesity at their primary health care centers.” However, according to questionnaires, this meant that only 54% of these patients received even some professional guidance. So, nearly half of the control group received no help at all from their healthcare providers with weight loss.
The Results: Surgery caused weight loss and prevented diabetes
These two figures say it all… compared to “customary treatment” in this cohort of obese patients, the patients who got bariatric surgery lost significantly more weight (Figure S3) and had significantly less progression to type 2 diabetes (Figure 1A).