RESEARCH RAISES DOUBTS ON OBESITY'S EFFECT ON MORTALITY.

Byline: Gina Kolata The New York Times

The largest study ever conducted of the health risks of obesity has found that it increases the likelihood of premature death but not as much as many medical experts had suspected.

The research, being published today in The New England Journal of Medicine, analyzed the fates of 324,135 white adults who were followed for 12 years. The study found that the excess risk of dying associated with being fat was relatively modest and declined as people grew older. By age 65, the increased risk was slight, and by age 74 it had disappeared.

People who were moderately overweight but not obese had no increased risk of premature death, the study found.

Medical experts who discussed the results disagreed about how to advise Americans. Some, including the lead author of the study, said any increased risk of premature death was reason enough to view obesity as a serious public health hazard.

Others said the dangers of obesity had been exaggerated, and that Americans' faith in the redemptive powers of weight loss might be misplaced.

The two top editors of the journal wrote in an editorial that losing weight was ``an ill-fated New Year's resolution.''

``The cure for obesity may be worse than the condition,'' the editors, Dr. Marcia Angell and Dr. Jerome P. Kassirir, wrote, explaining that the cures tend to be dire and ultimately ineffective.

Although there is a widespread belief that obesity places people at high risk of premature death and that when obese people lose weight they reduce their risk of dying young, previous studies were ``limited, fragmentary and often ambiguous,'' the two doctors wrote. And, they added, even though it is often said that obesity causes 300,000 deaths a year in the United States, ``that figure is by no means well-established.''

It was not clear why obesity should have smaller and smaller effects on death rates as people age. One hypothesis is that fat people who are susceptible to the calamitous consequences of excess weight die early, so those who remain are comparatively resistant to the effects of being fat, said Dr. Charles Hennekens, the chief of preventive medicine at Brigham and Women's Hospital in Boston.

The study did not look at the incidence of diseases associated with obesity, like diabetes, high blood pressure and high levels of blood cholesterol. About 6 percent to 8 percent of obese people develop diabetes, said Dr. Jules Hirsch, an obesity researcher at Rockefeller University, adding that ``diabetes heads the list'' of diseases associated with being fat.

The new study avoided many of the problems of earlier ones simply because it was huge, as large as all previous such studies combined, Hennekens said.