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Obesity Surgery: Hunger Hormone Impact

Findings Could Lead to Better Weight Loss Drugs
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.

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