Researchers at the Scripps Research Institute in California in the U.S. have developed an anti-obesity vaccine that significantly slowed weight gain and reduced body fat in rats even when they over ate.

The team say the vaccine represents a breakthrough in the global battle against obesity but warn it is a long way from being tested on human volunteers, and it may not work in people.

Even so the study has revealed how certain aspects of hunger and weight gain work.

The vaccine targets the hormone ghrelin, a gastric endocrine hormone produced primarily in the stomach, which was discovered in 1999 and helps control appetite in animals and people.

According to Dr. Kim Janda, a professor of Chemistry at Scripps Research, and a member of the Skaggs Institute for Chemical Biology, the active vaccination against ghrelin appears to be one avenue that can slow weight gain and fat build-up in the body.

Dr. Janda says the vaccine achieved this even though the rats’ food intake was unchanged and those who were given the most effective vaccines gained the least amount of weight.

Janda says the vaccine also appears to help control whether the body stores fat or burns it off.

It seems ghrelin has to move from the bloodstream into the brain in order to have an impact on appetite and weight gain.

Janda believes the vaccine might help people avoid the weight loss and weight gain seen in “yo-yo” dieting and may provide a workable solution to the problem of obesity.

Janda says they looked at immunopharmacotherapy vaccines to treat obesity, because they engage the immune system - specifically antibodies - to bind to selected targets, directing the body’s own immune response against them, and drugs have been remarkably unsuccessful and are only effective while treatment is maintained.

Obesity remains a serious and growing problem for millions of people worldwide and is a contributing risk factor for a number of other diseases including heart disease, various cancers, type 2 diabetes, stroke, arthritis, and depression.

Recent reports from the World Health Organization estimate as many as 1 billion people worldwide are overweight or obese, most of them in the developed world.

In the United States the National Health and Nutrition Examination Survey found that, in 2003 to 2004, approximately 66 percent of all American adults 20 years of age or older were overweight or obese.

The study was supported by the National Institute of Diabetes, Digestive, and Kidney Disorders and The Skaggs Institute for Chemical Biology and is published in the Proceedings of the National Academy of Sciences.