Endocrinology Advisor sat down with David Nathan, MD, Director of the Diabetes Center at Massachusetts General Hospital in Boston, Massachusetts, to discuss takeaways for endocrinologists from the 4th World Congress on Interventional Therapies for Type 2 Diabetes (WCITD), held April 8 to 10, 2019, in New York City.

Endocrinology Advisor: Could you discuss your opinion on using some caution while interpreting data from the randomized controlled trial results on metabolic surgery in diabetes that have been discussed during WCITD 2019?

David Nathan, MD: We should keep in mind that at the last [Diabetes Surgery Summit II in 2015], which was the same group of people, we tried to stress at that time that we should not overpromise what obesity surgery accomplishes. What happened at the time of that Congress was that there was really some impressive work done (eg, Phil Schauer’s work in STAMPEDE), plus some of the studies that are now cited as those 12 clinical trials, but the bottom line is they are generally too short in duration and too limited in number to demonstrate the longer-term effects.

We know from doing lots of studies, whether its cardiovascular outcome trials for the new diabetes drugs or studies of diabetes treatments and interventions and what their effects are, that it takes a lot of people over a long period of time to demonstrate the benefits, and [during the panel discussions at WCITD 2019,] I wanted to be sure that we did not overinterpret what are still limited data in terms of microvascular disease, cardiovascular disease, and mortality.

The study that everyone continues to goes back to is the Swedish Obesity Study (SOS). It still represents the most powerful [data], but it was a nonrandomized trial and there were differences in the people who got the surgery and who did not get the surgery. We are still waiting to see a [randomized] study, and my guess is that it is going to be very difficult to do that. Who is going to fund that kind of study? It will need to follow potentially thousands of patients over at least 5 to 10 years depending on which outcomes you are looking at to really demonstrate that obesity surgery has benefits [with regard to microvascular and cardiovascular disease]. I think surgeons have demonstrated well that they have brought down the risks of the procedures themselves, but interestingly most of the data are for a procedure that is no longer being done [sic].

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It used to be that Roux-en-Y gastric bypass was the surgery that was done in most studies. But that has shifted because of safety and ease for the surgeon [to perform] sleeve gastrectomy. Patients do not lose quite as much weight — it is not quite comparable to [Roux-en-Y gastric bypass]. Everyone keeps talking on the one hand of the mechanisms that underlie the benefits of the surgery, but those mechanisms have been, to some extent, established largely with that older procedure… The new procedures are clearly safer, but [researchers] need to demonstrate this.

The premise of this meeting was that if obesity surgery is so great and we now have guidelines in place, why are so few people getting [metabolic surgery] compared with the huge number of people who could be getting it? The reasons for that are complicated.