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Obesity Surgery: Hunger Hormone Impact

Findings Could Lead to Better Weight Loss Drugs
By
WebMD Health News
Reviewed by Louise Chang, MD

May 12, 2006 -- New research offers more evidence that weight loss surgery has a dramatic impact on the hormones that drive hunger, and the findings could help advance the search for better drugs to treat obesity.

The study involved nine morbidly obese patients who had gastric bypass surgery.

Just six weeks after surgery, secretions of the hunger-reducing hormones peptide YY (PYY) and glucagons-like peptide 1 (GLP-1) were significantly altered in the patients. Although patients had lost weight, they "were still markedly obese," write the researchers.

Surgery and Satiety

PYY and GLP-1 have been shown to play a role in appetite control by signaling the body that it is no longer hungry after meals.

Blood tests were done to check the levels of PYY and GLP-1 after fasting and also after drinking a liquid test meal. Prior to surgery, the researchers found that secretions of the two hormones were not increased in response to the liquid test meal as would be expected.

Six weeks after surgery, the hormones were significantly elevated in the nine patients after they consumed the same test meal. PYY and GLP-1 hormonal responses after meals were twice as great in the surgically treated patients as in obese patients who did not have the surgery, even though the subjects in both groups had similar BMIs.

The fasting levels of PYY and GLP-1 six weeks after surgery were not significantly increased from the levels before surgery.

Participants' hunger ratings were lower after surgery compared with before surgery. The ratings were especially lower after consuming the test meal.

The findings, reported in the May issue of The Journal of Clinical Endocrinology and Metabolism, suggest that it is the surgery itself that drives the hormonal changes and not the weight loss that results from it.

"We know that something is going on with hunger following weight loss surgery, and we believe that it is related to hormones," researcher Josep Vidal, MD, PhD, tells WebMD. "But we probably don't have the whole picture yet."

Investigating Hunger Hormones

Just a few years ago, most research was focused on the appetite-stimulating hormone ghrelin. Studies showed dramatic differences in ghrelin secretions among obese patients who had undergone gastric bypass operations and those who had other types of surgery or no surgery at all.

But it quickly became clear that ghrelin did not tell the whole story, and research efforts have broadened to include other appetite-regulating hormones like PYY and GLP-1.

At least one GLP-1-like substance is under investigation as an appetite suppressant.

Vital and colleagues say their findings, if confirmed, could lead to the development of new weight loss drugs that mimic the hormonal changes seen with surgery.

Obesity researcher Nana Gletsu, PhD, of Atlanta's Emory University School of Medicine, tells WebMD that future weight loss drugs will probably target hormones in the brain and the hunger hormones found in the gut.

But she adds that there is more to hunger than hormones.

"Hunger and satiety are very complex," she says, "Hormones certainly influence hunger, but so do mental and environmental factors, such as time of day and stress levels. You may have hormones from your stomach telling you that you are hungry or full, but they are not the only signals you are receiving."

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