Hormone that signals 'full feeling' could fight the flab

A hormone that signals when the stomach is full has been found to cut the appetites of both fat and thin people by one-third in an experiment that could signal an important advance in the treatment of obesity.

Professor Stephen Bloom, of Imperial College London and Hammersmith Hospital, who headed the team that made the discovery, said it was the first time in 20 years that they had identified a compound with such potential. The finding is published in The New England Journal of Medicine.

"Breakthrough treatments for obesity have been reported twice a week for a decade," said Professor Bloom, "but you have got to distinguish the ones that are serious. We have spent a tremendous amount of time and effort on this area."

The hormone, code-named PYY3-36, is produced naturally in the gut in response to food and tells the brain when the appetite has been satisfied. The Hammersmith researchers found that levels were lower in fat people than in thin people, suggesting that one cause of obesity may be a deficiency in the satiety mechanism. They decided to test whether giving more of the hormone would suppress their appetites.

A group of 24 volunteers, half obese and half thin, were asked to go without breakfast and attend Hammersmith Hospital at 8.30am, where they were given a 90-minute infusion of the hormone or a placebo salt solution. Two hours later they were allowed to eat as much as they liked of a buffet meal.

All the volunteers ate less on the day they received the hormone infusion. They also reported feeling less hungry. The average reduction in the amount eaten was one-third.

The most significant previous "breakthrough" was the discovery of the hormone leptin in the Nineties, which signalled how much fat was stored in the body. Low levels encouraged the body to build up its fat stores, so giving more of the hormone should theoretically have helped curb obesity.

But in 1997 researchers discovered that obese people were resistant to leptin for reasons that are still not understood. The key difference with PYY3-36 is that the new study has shown it works on thin and fat people.

Rachel Batterham, the lead researcher, said: "If you gave a thin person the same meal as an obese person, the level of PYY3-36 would go up less in the obese person. That is why the obese snack a lot - they feel continuously hungry. It is very difficult to lose weight if you are obese."

The best option for developing the research would be to find a food or foods that triggered release of PYY3-36 in the gut, she said. Some evidence suggests that certain types of high-fibre foods - those with viscous fibre covering the cells, such as apples, that makes them hard to digest - could promote the release and help curb appetite.

The Hammersmith research, funded by the Wellcome Trust, could lead to the development of an effective treatment in five years, Professor Bloom said.

The advantage of PYY3-36 is that as a naturally occurring hormone it should be "completely safe and effective", he said. "You have had 40,000 infusions already - after every meal - and no side-effects. This could be a really promising treatment for millions of people in the UK."

Ian Campbell, chairman of the National Obesity Forum, said the finding raised hopes of better treatments for obesity. But he warned: "We have been here before, and nothing has yet materialised."