Some Extra Heft May Be Helpful, New Study Says

By GINA KOLATA
New York Times

People who are overweight but not obese have a lower risk of death than those of normal weight, federal researchers are reporting today.

The researchers – statisticians and epidemiologists from the National Cancer Institute and the Centers for Disease Control and Prevention – also found that increased risk of death from obesity was seen for the most part in the extremely obese, a group constituting only 8 percent of Americans.

And being very thin, even though the thinness was longstanding and unlikely to stem from disease, caused a slight increase in the risk of death, the researchers said.

The new study, considered by many independent scientists to be the most rigorous yet on the effects of weight, controlled for factors like smoking, age, race and alcohol consumption in a sophisticated analysis derived from a well-known method that has been used to predict cancer risk.

It also used the federal government’s own weight categories, which define fatness and thinness according to a "body mass index" correlating weight to height, regardless of sex. For example, 5-foot-8 people weighing less than 122 pounds are underweight. If they weighed 122 to 164 pounds, their weight would be normal. They would be overweight at 165 to 196, obese at 197 to 229, and extremely obese at 230 or over.

Researchers had a full gamut of responses to the unexpected findings, being reported today in The Journal of the American Medical Association.

Some saw the report as a long-needed reality check on what they consider the nation’s near-hysteria over fat.

"I love it," said Dr. Steven Blair, president and chief executive of the Cooper Institute, a research and educational organization in Dallas that focuses on preventive medicine.

"There are people who have made up their minds that obesity and overweight are the biggest public health problem that we have to face," Dr. Blair said. "These numbers show that maybe it’s not that big."

Others simply did not believe the findings.

Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women’s Hospital in Boston, which is affiliated with Harvard, pointed to the university’s own study of nurses that found mortality risks in being overweight and even greater risks in being obese. (That study involved mostly white women and used statistical methods different from those in the newly reported research.)

"We can’t afford to be complacent about the epidemic of obesity," Dr. Manson said.

In fact, the new study addressed the risk only of death and not of disability or disease. There has long been conclusive evidence that as people move from overweight to obese to extremely obese, they are more and more likely to have diabetes, high blood pressure and high cholesterol levels.

But the investigators said it was possible that being fat was less of a health risk than it used to be. They mentioned a paper, also being published today in the journal, in which researchers including Dr. Edward W. Gregg and Dr. David F. Williamson, both of the C.D.C., report that high blood pressure and high cholesterol levels are less prevalent now than they were 30 or 40 years ago, largely because of breakthroughs in medication.

As for whether there is truly a mortality risk in being underweight, Dr. Mark Mattson, a rail-thin researcher at the National Institute on Aging who is an expert on caloric restriction as a means of prolonging life, said it was not clear that eating fewer calories meant weighing so little, since some people eat very little and never get so thin. In any event, while caloric restriction may extend life, Dr. Mattson said, "there’s certainly a point where you can overdo it with caloric restriction, and we don’t know what that point is."

Some statisticians and epidemiologists said that the study’s methods and data were exemplary and that the authors – Dr. Williamson and Dr. Katherine M. Flegal of the disease control centers, and Dr. Barry I. Graubard and Dr. Mitchell H. Gail of the cancer institute – were experienced and highly regarded scientists.

"This is a well-known group, and I thought their analysis and their statistical approaches were very good," said Dr. Barbara Hulka, an emerita professor of epidemiology at the University of North Carolina.

The study did not explain why overweight appeared best as far as mortality was concerned. But Dr. Williamson said the reason might be that most people die when they are over 70. Having a bit of extra fat in old age appears to be protective, he said, giving rise to more muscle and more bone.

"It’s called the obesity paradox," Dr. Williamson said. But, he said, while the paradox is real, the reasons are speculative. "It’s raw conjecture," he said.

The new study comes just 13 months after different researchers from the disease control centers published a paper warning that obesity and overweight were causing an extra 400,000 deaths a year and were poised to overtake smoking as the nation’s leading preventable cause of premature death.

That conclusion caused an uproar, and scientists, particularly those who examine the consequences of smoking, questioned the study’s methods. In January, the agency’s researchers corrected calculation errors and published a revised estimate of 365,000 deaths.

Now the new study says that obesity and extreme obesity are causing about 112,000 extra deaths but that overweight is preventing about 86,000, leaving a net toll of some 26,000 deaths in all three categories combined, compared with the 34.000 extra deaths found in those who are underweight.

Dr. Donna Stroup, director of the Coordinating Center for Health Promotion at the C.D.C., noted that the previous study had used different data and different methods of analysis.

"Counting deaths is not an exact science," Dr. Stroup said.

For now, said Dr. Dixie Snider, the disease control centers’ chief science officer, the agency will not take a position on what is the true number of deaths from obesity and overweight. "We’re too early in the science," Dr. Snider said.

Dr. Stroup said of the new findings, "From a scientific point of view, they are a step forward." But she added that the agency considered illness that is linked to obesity to be just as important as the number of deaths.

"Mortality really only represents the tip of the iceberg of the magnitude of the problem," she said.

Estimating deaths due to overweight or obesity is a statistical challenge, the study’s investigators said. The idea is to determine, for each person in the population, what would be the risk of dying if that person’s weight were normal.

For people whose weight is already in that range, there would be no change in the risk, of course. But what happens to the risk for people whose weight is above or below the normal range? The idea is to control for factors like age, smoking and gender, and ask what would happen if only the weight were changed.

Now that the researchers have done their analysis, Dr. Williamson said, the message, as he sees it, is that perhaps people should take other factors into consideration when deciding whether to worry about the health risks of their weight.

Dr. Williamson, who is overweight, said that "if I had a family history – a father who had a heart attack at 52 or a brother who developed diabetes – I would actively lose weight."

But "if my father died at 94 and my mother at 97 and I had no family history of chronic disease," he said, "maybe I wouldn’t be as concerned."

Dr. Barry Glassner, a sociology professor at the University of Southern California, had another perspective.

"The take-home message from this study, it seems to me, is unambiguous," Dr. Glassner said. "What is officially deemed overweight these days is actually the optimal weight."