Scientists have identified a human hormone that naturally reduces appetite and say it could become a drug to help combat the worldwide rise in obesity. British, U.S., and Canadian researchers report in the current edition of the journal "Nature" that a hormone produced in the intestine lowered appetite in people injected with it.
Study leader Stephen Bloom, a physician at Imperial College in London, says 12 normal weight volunteers ate one-third less at a free buffet than others injected with a salt solution. Furthermore, they stayed full for up to 12 hours without snacking. "We were very surprised to find that actually it was a powerful inhibitor of appetite," he says. "So it appeared to be normally controlling everybody's appetite, so we've called it the hormone of satiety."
The hormone, called PYY-336, rises in the blood after eating in proportion to the amount consumed and remains high between meals. The scientists believe it travels to the brain, where it shuts down nerves that trigger eating.
PYY-336 is one of several hormones that play different roles in appetite control. One identified last year by Dr. Bloom's laboratory, a chemical called ghrelin, is secreted before a meal to boost hunger, then goes away immediately after eating.
PYY apparently is then activated to suppress appetite until the next meal. "This appears to explain a lot of the reason why when you've eaten a meal, you no longer feel hungry. This has been a physiological puzzle for some time," says. Dr. Bloom. "It now seems it's these hormones that detect how much nutriment you have eaten and they switch off your appetite according to the size of the meal."
Dr. Bloom says it may be possible to create a drug with similar effects to help obese people control their food intake. The World Health Organization says 300 million people worldwide are obese, a 50 percent increase since 1995.
But University of Washington physician Michael Schwartz warns that drug treatments must mimic all the appetite regulation hormones because they work together in the body in a complementary way. Lowering only PYY, for example, might increase the hormone ghrelin because in mammals, ghrelin secretion goes up to boost hunger when PYY is down. Similarly, loss of body fat causes increases in another hunger promotion hormone, leptin. Dr. Scwhartz says this must be taken into account, too. "So in the end, combinations of drugs that target this regulatory system at multiple points are the ones that I think will be most effective because the idea is to get the individual to lose weight, but at the same time block the compensatory response, because it's that compensatory response that is what drives people to regain weight that they lost in the first place."
In London, Stephen Bloom says drugs based on natural hormones would be far more effective than current diet pills or surgery. "Suddenly we're out of the dark ages as far as appetite control is concerned and we have effective substances," he says. "It's only going to be a matter of time before they are tested and we can start to treat people."