But not all bariatric procedures have the same effect on weight and diabetes: certain procedures have a greater effect.
The two major types are classified as gastric restrictive procedures and intestinal bypass procedures. The classification was initially based on the presumed mechanism of weight loss.
Gastric restrictive procedures (laparoscopic adjustable gastric banding, sleeve gastrectomy, vertical gastroplasty) limit gastric volume and, hence, restrict the intake of calories by inducing satiety. Afterward, patients lose approximately 10% to 20% of their total body weight.
Furthermore, multiple studies, including a randomized controlled trial 14 (more about this below), have shown remission of type 2 diabetes with laparoscopic adjustable gastric banding but not with conventional medical therapy. The effect is primarily mediated by weight loss and improved insulin sensitivity, both of which occur several months following surgery. Of note, however: in this trial, 14 all the patients had diabetes of short duration, less than 2 years.
Intestinal bypass procedures (Roux-en-Y gastric bypass, biliopancreatic diversion) also restrict caloric intake, the way gastric banding and vertical gastroplasty do. But because the small intestine is shortened, they have an added component of malabsorption of fat and nutrients. Afterward, more patients experience remission of type 2 diabetes (82%–99%) than after gastric restrictive operations, even patients with longer duration of disease, including those treated with insulin ( Table 1 ).12,13
Hence, different procedures have different effects on diabetes. 12 The speed at which type 2 diabetes goes into remission differs with restrictive vs malabsorptive procedures. After Roux-en-Y gastric bypass and biliopancreatic diversion, diabetes remits within days, even before the patient has lost much weight. 15 This does not happen after gastric restrictive procedures. 12,16
Observational studies of the effect of Roux-en-Y surgery on diabetes
Several observational studies have evaluated the benefit of Roux-en-Y surgery for patients with type 2 diabetes mellitus.
Pories et al 15 followed 608 severely obese patients, of whom 165 (27%) had type 2 diabetes or impaired glucose tolerance.
At a mean follow-up of 7.6 years after surgery, 83% of the diabetic patients were off their antidiabetic drugs, and 99% of those with impaired glucose tolerance were normoglycemic, with normal fasting glucose and hemoglobin A 1c levels. Marked improvements in hyperlipidemia, hypertension, fertility, osteoarthritis, and obstructive sleep apnea were also noted.
Schauer et al 17 observed similar results in 1,160 morbidly obese patients, of whom 240 (21%) had type 2 diabetes or impaired fasting glucose.
After laparoscopic Roux-en-Y gastric bypass surgery, fasting glucose and hemoglobin A 1c levels returned to normal levels in 83% of cases and were markedly improved in the remaining 17%. Significantly (80%) fewer patients needed oral antidiabetic agents or insulin (79% fewer). Patients most likely to achieve complete remission of diabetes were those with the shortest duration of diabetes (< 5 years), the mildest severity of diabetes (diet-controlled), and the greatest weight loss after surgery. The rate of diabetes remission in patients who had been diabetic for 5 years or less was 95%, compared with 75% in those who had been diabetic for 6 to 10 years and 54% in those who had been diabetic for more than 10 years ( P < .001).