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updated 6/10/2011 12:47:10 PM ET 2011-06-10T16:47:10

Obese people may one day be able to get a vaccine to help them lose weight, a new study in mice suggests.

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The vaccine is designed to block the appetite-stimulating hormone ghrelin. Mice injected with the vaccine ate less and burned more calories than mice not given the vaccine.

If such a vaccine were developed for human use, it would have advantages over current weight-loss drugs, which have side effects and cannot be used over the long term, said study researcher Dr. Mariana Monteiro, an associate professor at the University of Porto in Portugal. For example, the drug Merida was withdrawn from the market last year because of concerns it could increase heart attack and stroke risks.

In contrast, the vaccine, appears to be safe so far, and its effects on the mice may last for years, the researchers said.

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However, other experts argue that while an obesity vaccine sounds appealing, in reality, the body's way of regulating appetite and weight gain is too complex for a vaccine to solve.

"I think that an obesity vaccine is pretty far-fetched," said Dr. Pieter Cohen, an assistant professor of medicine at Harvard Medical School and a general internist at Cambridge Health Alliance. "It's extremely unlikely we'll be able to develop a vaccine that will prevent weight gain," Cohen said.

Obesity vaccine
To develop the vaccine, Monteiro and her colleagues attached ghrelin to harmless, viruslike particles. The idea is that once injected, the body's immune system will develop antibodies against ghrelin, suppressing the hunger-causing hormone.

Obese mice ate 50 percent less food after receiving the vaccine (three shots in total) than mice who did not receive the vaccine. The vaccinated mice also expended more energy.

The vaccine's appetite-suppressing effects lasted for 18 months in the mice, which is the equivalent of four years in people, Monteiro told MyHealthNewsDaily.

More work is needed to find whether suppressing ghrelin affects other body processes over the long term, Monteiro said. Ghrelin is involved in other functions, including bone turnover, she said.

A 2006 study also showed it was possible to block ghrelin in animals using a vaccine. But Monteiro's study used a different approach for generating the immune response, which she says is safer

A complex problem
Many signals in the body regulate appetite and energy expenditure, and it's unrealistic to think a vaccine targeting one hormone could do the trick in terms of weight loss, Cohen said.

Other experts agree. "Most of us are skeptical that 'turning off the ghrelin switch' is the universal answer to all obesity," said Dr. Sunil Bhoyrul, a bariatric surgeon at Scripps Memorial Hospital in La Jolla, Calif.

While the study is "good science," it's just "the first step in a medical approach to a complex problem," Bhoyrul said. Researchers need to study patients' DNA to have a better understanding of why certain individuals become obese, and how to treat their obesity, he said.

The new study was presented June 5 at the annual meeting of Endocrine Society in Boston.

Pass it on: An "obesity vaccine" is a good idea, but isn't yet ready for human use. 

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Follow MyHealthNewsDaily staff writer Rachael Rettner on Twitter @RachaelRettner.

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