Obesity Surgery: Hunger Hormone Impact
Findings Could Lead to Better Weight Loss Drugs
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
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
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
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
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."