TUESDAY, Jan. 1 (HealthDay News) -- A new international analysis reveals a surprising pattern: while obesity increases the risk of dying early, being slightly overweight reduces it.
These studies included almost 3 million adults from around the world, yet the results were remarkably consistent, the authors of the analysis noted.
"For people with a medical condition, survival is slightly better for people who are slightly heavier," said study author Katherine Flegal, a senior research scientist at the U.S. Centers for Disease Control and Prevention's National Center for Health Statistics.
Several factors may account for this finding, Flegal added.
"Maybe heavier people present to the doctor earlier, or get screened more often," she said. "Heavier people may be more likely to be treated according to guidelines, or fat itself may be cardioprotective, or someone who is heavier might be more resilient and better able to stand a shock to their system."
The report was published Jan. 2 in the Journal of the American Medical Association.
For the study, Flegal's team collected data on more than 2.88 million people included in 97 studies. These studies were done in the United States, Canada, Europe, Australia, China, Taiwan, Japan, Brazil, Israel, India and Mexico. The researchers looked at the participants' body mass index, or BMI, which is a measurement of body fat that takes into account a person's height and weight.
Pooling the data from all the studies, the researchers found that compared with normal weight people, overweight people had a 6 percent lower risk of death. Obese people, however, had an 18 percent higher risk of death.
For those who were the least obese, the risk of death was 5 percent lower than for normal weight people, but for those who were the most obese the risk of death was 29 percent higher, the findings revealed.
While the study found an association between weight and premature death risk, it did not prove a cause-and-effect relationship.
Indeed, one expert cautioned that body weight alone cannot predict health and the risk of death.
"There are other factors that play a role in overall health," said Dr. William Cefalu, chief and professor of the section of endocrinology, diabetes and metabolism at Louisiana State University and co-author of an accompanying journal editorial.
"Body mass index simply is a parameter; it doesn't take into consideration family history, it doesn't take into consideration smoking, fitness, cholesterol and other factors that should be considered beyond body mass index," he said.
Another expert agreed and added that the issues around body weight are more complicated than this study suggests.
"This is a large, sophisticated and statistically powerful study that shows convincingly that more severe degrees of obesity increase the risk of premature death, while being merely overweight does not," said Dr. David Katz, the director of the Yale University Medical School Prevention Research Center.
"Like the study itself, the messages here are a bit complex," Katz added.
There is a case to be made that a body mass index in what is now considered the overweight range might be redefined as normal, Katz said. "If weight is not harmful to health, there is no reason to suggest otherwise," he said.
This study, however, looks only at death, not chronic medical conditions, Katz noted.
"It may well be being overweight does increase the risk of such conditions as type 2 diabetes, or medication use for cardiac risk factors, without increasing mortality. This study would be blind to such effects," he said.
Katz also noted the trends in obesity may be tipping the scale toward increased risk of dying.