If there’s anything we’ve learned conclusively about human health in the last few decades, it’s that smoking is lethal and obesity increases the risk of dying early. But to the surprise of many (and the skepticism of others), an international analysis shows that being slightly overweight may lead to a longer life.

The new report analyzed 97 international studies and revealed notably consistent results, say the authors of the findings that were published in the most recent Journal of the American Medical Association.

"For people with a medical condition, survival is slightly better for people who are slightly heavier," noted the study leader, Katherine Flegal, a senior research scientist at the Centers for Disease Control and Prevention's National Center for Health Statistics.

The collection of studies included data on more than 2.88 million people in countries as diverse as the United States, Canada, Europe, Australia, China, Taiwan, Japan, Brazil, Israel, India and Mexico.

Using Body Mass Index (BMI) figures, the data from all the studies were combined. The team found that compared with normal weight people, overweight people had a 6 percent lower risk of death. However, obese people were found to have an 18 percent higher risk of death.

For 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.

Although the study revealed the numbers and an association between weight and early death risk, it did not prove why.

"Maybe heavier people present to the doctor earlier, or get screened more often," Flegal 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."

Other experts note that body weight alone cannot predict health and the risk of death.

"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, director of the Yale University Medical School Prevention Research Center.

However, Katz added, "Like the study itself, the messages here are a bit complex. Moving from overweight to obese, and from obese to more obese, is a serious peril and many in the population are doing exactly that.”

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A little extra fat may actually prolong life
A new study finds a link between being slightly overweight and living longer.