With restrictive weight loss procedures, insulin resistance drops as weight loss increases, whereas with malabsorptive operations, resistance is completely reversed even before body weight normalizes, new research shows.

The findings, are based on a study of 18 nondiabetic patients with severe obesity and 20 lean controls who underwent various metabolic evaluations, including insulin sensitivity testing.

Restrictive weight loss surgery, such as gastric bypass, involves limiting the stomach size, ultimately causes the patient to eat less. In contrast, with malabsorptive operations, such as biliopancreatic diversion, the intestines are rearranged in such a way that the patient absorbs less of what is eaten.

The new findings indicate that with restrictive operations, the improvement in insulin sensitivity depends on the degree of weight loss. With malabsorptive operations, however, normal insulin sensitivity is restored more rapidly and is not dependent on the amount of weight loss.

The patients were treated with either gastric bypass, a restrictive type operation, or with biliopancreatic diversion, a malabsorptive procedure, and were reevaluated 5 to 6 months and 16 to 24 months postoperatively. The bypass operation involved vertical banded gastroplasty with standard Roux-en-Y reconstruction.

Compared controls, the obese patients were hyperinsulinemic, hypertriglyceridemic, and were profoundly insulin resistant at baseline, senior author Dr. Ele Ferrannini, from the University of Pisa in Italy, and colleagues note.

With each procedure, weight loss averaged 53 kg and occurred over roughly the same time course. However, as noted, the operations differed in their effects on insulin resistance.

During follow-up, a steady improvement in insulin sensitivity was seen in the gastric bypass group, but even at 16 months, values were still significantly low compared with those seen in controls.

In the biliopancreatic diversion group, by contrast, insulin sensitivity normalized by 6 months and actually exceeded that of controls at 24-month follow-up, even though the subjects were still obese.

While the results suggest that biliopancreatic diversion restores insulin sensitivity more rapidly than gastric bypass, the authors note that "the choice of the optimal therapeutic strategy in these patients depends on a risk/benefit algorithm to be assessed in each patient."

Source: Diabetes In Control.com: Am J Med 2005;118:51-57.