An obesity vaccine has been developed that uses the immune system to keep the body slim.
The "flab jab" has shown promising early results in mouse studies.
If the vaccine passes further safety trials, scientists believe it could provide a revolutionary new weapon against obesity.
Currently the only non-dieting options for controlling weight are surgery and strong drugs that can have serious side effects.
The vaccine works by stimulating the immune system to attack a hormone that promotes slow metabolism and weight gain.
In tests, obese mice fed a high fat diet saw a 10% drop in body weight four days after receiving the jab.
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Two slightly different versions of the vaccine were studied. Both produced a sustained 10% reduction in body weight after booster injections were administered after three weeks.
The slimming effect was not seen in a matched group of 10 untreated mice.
Lead researcher Dr Keith Haffer, from the US company Braasch Biotech in South Dakota, said: "This study demonstrates the possibility of treating obesity with vaccination.
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"Although further studies are necessary to discover the long term implications of these vaccines, treatment of human obesity with vaccination could provide physicians with a drug and surgical-free option against the weight epidemic."
Research published last year in The Lancet medical journal showed that almost half of all British men could be obese within 20 years.
The proportion of men meeting the clinical definition of obesity was predicted to rise from around 20% to between 41% and 48%.
Being obese is defined as having a Body Mass Index (BMI) - a measurement relating height and weight - of 30 or more.
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More women in the UK are also becoming obese. By 2030, four in 10 British women could be at obese weight levels, the research shows.
Up to 30,000 Britons die prematurely every year from obesity-related conditions. Obesity has been estimated to cost the NHS at least £500 million a year, and the UK economy more than £2 billion.
The new vaccine uses a modified form of somatostatin, a peptide protein molecule that functions as a hormone.
In both mice and humans somatostatin suppresses growth hormones that boost metabolism and cause weight loss.
The vaccine "flags up" somatostatin so that it is seen as a potential threat by the immune system. It causes the body to generate antibodies that neutralise the peptide.
In mice, the vaccine reduced body weight without affecting normal levels of growth hormones.
Reporting their findings in the Journal of Animal Science and Biotechnology, the scientists wrote: "The vaccination effects did not significantly reduce cumulative food consumption and was confirmed by residual anti-somatostatin antibodies in mouse plasma at the study's end."
Although the mice received large amounts of the vaccine, a recent unpublished study in pigs suggested it was effective at much lower doses.
Further research will look at the vaccine's effects in obese pigs and dogs before moving onto human trials.