Hormone may hold key to treating obesity

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, from Imperial College, London and the 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. But you have got to distinguish the ones that are serious. We have spent a tremendous amount of time and effort on this area. We have got a team of 40 working on it. It's the Americans who suffer from obesity but we think we have found a way forward."

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 lean 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 were given a 90 minute infusion of the hormone , or of a placebo salt solution. Two hours later they were allowed to eat as much as they liked.

All 24 volunteers ate less on the day they received the hormone infusion than when they received the placebo. They also reported feeling less hungry. The average reduction in the amount eaten was one third.

There have been other "breakthroughs" before - and none has delivered on their early promise. The most significant was the discovery of the hormone leptin in the 1990s, 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 PYY is that the new study has shown that it works on both 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."

Dr Batterham said she had measured her own PPY level and found it was high. "That is because I am fairly thin. I am lucky - I don't put weight on."

The best option for developing the research would be to find a food or foods that triggered release of PYY 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 of PYY and help curb appetite.

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

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."

The researchers have still to show that the loss of appetite seen over 24 hours leads to significant weight loss when the treatment is given over months.

Professor Bloom said: "That is important. But my suspicion is that it will have a long term effect. There is no escape from it in nature."

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

- INDEPENDENT