Gastric bypass surgery is the most effective method for treating obesity—it’s 97% effective at reducing excess weight by more than 45% at least 1 year post-surgery. Dieting (irrespective of type) averages about 8% loss, though two-thirds of people regain more weight than they lost within 2 years.
So dieting does not work (in general), and gut surgery is very likely to work, but is it possible that neurosurgery will be even better? Deep brain stimulation (DBS) is the latest frontier in neurosurgery, and it is successful at accomplishing behavior change for many patients, including obese patients, but a controlled clinical trial has not yet measured its efficacy. To compare whether DBS or gastric bypass is better, you also need account for complications of each surgical type.
A study in the journal Neurosurgical Focus has calculated how effective DBS will have to be in order for it to be a better choice than gastric bypass, tasking both efficacy and complication rate into account: it will to be better than 83% effective to beat out gastric bypass at weight loss.
Whether DBS will be beneficial for diabetes remains to be seen.