There are two types of bariatric surgery for weight loss. One is gastric bypass and the other is adjustable gastric banding or "lap banding". Bypass surgery shrinks the size of the stomach by more than 90%, so less food can be comfortably eaten. This is good for reducing calories, but many vitamins and minerals are not absorbed as well. About 20% of patients who have the gastric bypass develop "dumping syndrome". In these cases, cramping and diarrhea occur because too much undigested food quickly passes into the intestine.
In lap banding a fluid-filled belt is wrapped around the stomach to form two stomach pouches. The tightness can be adjusted. Tighter bands make the patient feel full, eating less. This type of surgery is reversible and does not need to be permanent.
Weight loss helps type 2 diabetes patients however it is achieved. It seems, however, that gastric bypass helps type 2 diabetes even before weight loss occurs. Scientists are not sure yet how that happens.
The American Diabetes Association recommends that only those people with type 2 diabetes and a body mass index of 35 or greater consider gastric bypass surgery. The type of long-term studies which might show other benefits or dangers from the surgery are not yet available. There is always a risk when surgery is involved. However, others feel that the opportunity to not need medications to manage their blood glucose is worth the risk.
More information is available from WebMD at http://www.webmd.com/diet/weight-loss-surgery/weight-loss-what-happens-during-bariatric-surgery. To calculate your own body mass index, visit the National Institutes of Health webpage at http://www.nhlbisupport.com/bmi/.