Volunteers who were given infusions of the hormone before a meal ate about a third less food than they did without it, providing the first direct evidence that the substance may provide a potent new weapon against obesity.

"It looks promising," said Stephen Bloom, a professor of medicine at the Imperial College London who helped conduct the study, published in today's issue of The New England Journal of Medicine.

Bloom and other researchers cautioned, however, that the study was small and brief, so additional studies involving more people for longer periods must be conducted to determine whether the hormone can help people lose weight safely and keep it off.

The research is "a hopeful step in the right direction," said Dr. David Cummings, an obesity researcher at the University of Washington. "But there's a fairly large difference between reducing food intake for one meal and actual weight loss."

The hormone, called peptide YY 3-36 (or PYY for short), is produced by the digestive system as part of the body's natural appetite-control system. Bloom and his colleagues last year showed that PYY curbed the appetite of normal-weight people, and the new study was designed to see if it had the same effect on obese people.

In the study, researchers gave infusions of the hormone and then an inert saline solution to 12 obese people and 12 people of normal weight. The researchers then gave the subjects a buffet lunch and told them to eat as much as they wanted without telling them whether they had just received the hormone or the solution. The volunteers consumed about 30 percent less after the hormone, compared with when they were given the inert saline solution. The subjects also ate less over the next 24 hours, the researchers have found.

The researchers also have found that the obese people appeared to have less of the hormone in their bodies to begin with.

If future studies show promise, the substance could provide a better approach to appetite control than current diet drugs because it is a part of the body's natural hunger-regulation system.

Group again petitions FDA for removal of diet drug

WASHINGTON — A consumer advocacy group said yesterday that the diet drug Meridia has been associated with the deaths of 49 patients since it came on the market five years ago and renewed a petition to the Food and Drug Administration to ban the drug.

Public Citizen, which first petitioned the FDA on Meridia more than a year ago, supplemented its effort with new information from the FDA "adverse event" database through the end of March. In addition to the 49 deaths, Public Citizen said, 124 users have been hospitalized for serious heart and cardiovascular problems since the drug was approved.

FDA spokeswoman Laura Bradbard said no date had been set for a decision on the petition.

Meridia's manufacturer, Abbott Laboratories, said the drug is safe and has been used by more than 12 million people worldwide.