There’s this one, a small study that compared glucose control in the same patients before surgery (following the post-surgery diet) and after their surgery:
Glucose homeostasis improved in response to a reduced caloric diet, with a greater effect observed in the absence of surgery as compared with after RYGB. These findings suggest that reduced calorie ingestion can explain the marked improvement in diabetes control observed after RYGB.
and then there’s this one, where patients were divided into three arms (two different weight loss surgeries and one conventional medical therapy):
At 2 years, the average baseline glycated hemoglobin level (8.65±1.45%) had decreased in all groups, but patients in the two surgical groups had the greatest degree of improvement.
Interestingly, I’ve heard a theory that if WLS works to reverse diabetes, the mechanism might be cutting the vagus nerve. But the first study, albeit a short one, suggests that it’s the WLS diet that may be a factor.
I’m not a fan of weight loss surgery, so I’m hoping that more studies show the former. It certainly is relatively easy to test compared to doing surgery.