Researchers at Imperial College London believe the treatment, an injection of a natural digestive hormone called oxyntomodulin that is released in the small intestine, could help to stem the world's growing obesity epidemic.

"The discovery that oxyntomodulin can be effective in reducing weight could be an important step in tackling the rising levels of obesity in society," said Professor Steve Bloom, who headed the research team.

The injection switches off the appetite so people eat less.

In a four-week trial of 26 people, volunteers who were given three injections of the treatment each day 30 minutes before meals lost an average of 2.3 kilos (5 lb). A control group that had saline injections lost about half a kilo (1 lb) (p = .01016).

Oxyntomodulin injections were associated with "transient mild nausea" in 3% of occasions, compared to 0.2% of saline injections (p = .0389).

Bloom and his colleagues, who reported their findings in the journal Diabetes, said it was still early days and more research needed to be done. But they have already set up a company called Thiakis to develop the treatment, which they hope will be available by prescription in about five years.

They initially envision it as a treatment for people who are overweight or obese and have a medical problem. But once it is established it could be rolled out more widely.

Bloom and his colleagues have developed a once-a-day injection and are looking into delivering the treatment through a nasal spray.

"When it comes to taking a pill with water or taking a disposable syringe with a super-fine needle and pressing the plunger, it really isn't very difficult," Bloom said.