Finally, for severely obese people with type 2 diabetes who have been unable to lose weight using traditional means, gastric-bypass or reduction surgery, also called bariatric surgery, may be an option. Only patients with a BMI greater or equal to 35 are typically considered for bariatric surgery.

There are a number of different types of bariatric surgery, including adjustable gastric banding, vertical-banded gastroplasty, Roux-en-Y gastric bypass, and biliopancreatic diversion (with or without a duodenal switch). The first two of these are restrictive surgeries, and work by closing off the majority of the stomach to the digestive process, leaving only a small section to digest food. The latter two are bypass (or malabsorptive) operations, which reroute the digestive flow past part or all of the small intestine to minimize the amount of calories absorbed.

Laparoscopic adjustable banding (also called lap banding) is a relatively new surgical procedure that is growing in popularity. As in traditional adjustable gastric banding, a portion of the stomach is banded off with a device that can be inflated or deflated to change the size of the stomach pouch as required. However, lap banding uses a minimally invasive laparoscopic procedure involving small incisions and the use of surgical cameras to position the band. This technique minimizes both recovery time and the risk of complications (as compared to traditional bariatric surgery).

Bariatric surgery carries the same risks of infection and hemorrhage as any major surgery, plus a high rate of related complications; up to 20 percent of people who have bariatric surgery have to undergo a follow-up operation to fix abdominal hernia or other problems. Gallstones are also a risk because of the rapid weight loss that occurs following the operation.

And because some types of surgery bypass the small intestine, where a great deal of nutrient absorption takes place, approximately 30 percent of patients end up with deficiencies of certain vitamins and minerals (a condition that can usually be corrected with supplementation).