Appetite Hormone Could Cut the Fat

British, US and Australian scientists have tested a natural hormone that makes people eat less.

Healthy volunteers treated with the hormone - it has the unappetising name of PYY3-36 - ate a third less than normal when invited to graze from a buffet of chicken curry, fruit salad, chocolate bars and other delights.

"The discovery that PYY3-36 suppresses appetite could be of huge benefit to those struggling with weight problems," said Stephen Bloom of Imperial College, London. "With over a billion people across the world now extremely overweight, it is vital this problem is tackled."

The hormone is naturally produced in the gastrointestinal tract after every meal. One of its functions is to circulate in the bloodstream and tell the brain that the diner is no longer hungry. Researchers at Hammersmith hospital, two laboratories in Oregon and the Garvan Institute of Medical Research in Sydney report in Nature today that they fed either an infusion of the hormone or salt water into the veins of 12 volunteers. Those who got the hormone drip received only the quantity that they would have produced themselves, naturally, after eating a normal meal.

Two hours later, they let the volunteers loose on a tempting buffet devised by the hospital's dietetics department. The diners who had the extra hormone consumed on average one third fewer calories in the following 24 hours. They also reported a 40% drop in perceived levels of hunger in the 12 hours after the infusion.

"We have always known that hunger is determined by complex interactions between the brain, hormones and enzymes in the gut," said Rory Shaw, medical director at the Hammersmith hospital. "But this discovery - that administering a particular hormone can actually reduce appetite - is a major step forward on the road to the development of a new, safe and effective treatment for obesity."

In Britain, 31,000 people die prematurely each year because of obesity. One adult in five is dangerously overweight. More than half of all British children are overweight and around a million are clinically obese. Overeating, in effect, costs the NHS more than £2.5bn a year, according to a national audit office study. Even in the developing world, obesity is a problem, bringing with it risks of illnesses such as asthma, diabetes, cancer and heart disease.

In the US, nearly two-thirds of the population is overweight, and one quarter of the population is clinically obese.

Researchers in Europe and the US have begun to identify genes that could play a role in obesity. Laboratories have been experimenting with leptin, a natural protein which seems to regulate the human appetite for fat. Direct medical interference is not, however, a long-term answer. The safest solution, experts agree, is to eat less and exercise more.

The PYY3-36 hormone experiments could point the way to a compromise.

"It may be possible to identify foods which cause the release of more PYY3-36, helping to naturally limit appetite, or it may be possible to create a tablet with a similar effect, providing an excellent, natural and safe long-term treatment for obesity," Prof Bloom said.

The next step is to test ways of delivering the hormone subcutaneously in obese volunteers, to see whether that has an effect. Any so-called "appetite pill" is a long way off. The hormone probably has many other functions in the body as well. These must also be investigated.