Weight-loss surgery works not just by restricting the amount of food absorbed by the body, it seems. In part, at least, it leads to weight loss by causing hormone changes that reduce appetite and improve sugar metabolism, new research suggests.

If these changes can be mimicked with drugs, it could lead to new treatments for severe obesity, the researchers note.

As reported in the Annals of Surgery, Dr. Stephen R. Bloom, from Imperial College London, and colleagues assessed how stomach or intestinal bypass operations affected hormones secreted by the gut in humans and in rodents.

Patients who underwent stomach bypass had increased levels of two hormones, PYY and GLP-1, which would be expected to produce sensations of fullness after eating, the report indicates. In addition, these patients had changes in their insulin response that would lead to improved blood sugar levels.

By contrast, patients who lost a comparable amount of weight through gastric banding, a procedure in which the size of the stomach is restricted but it’s not actually bypassed, did not show these hormonal changes, the authors point out.

In rats, intestinal bypass seemed to cause similar changes in PYY and GLP-1 as did stomach bypass did in humans, the report indicates.

“Following bypass surgery, it is likely that multiple mechanisms act in concert to achieve sustainable weight loss,” the investigators note. “Replicating the hormonal milieu that arises as a consequence of (stomach) bypass surgery” with medications holds promise as a treatment for obesity in the future.

SOURCE: Annals of Surgery, January 2006.