In a newly published study, people who were underweight and those who were extremely obese died the earliest.
People who were overweight, but not obese, actually lived longer than people whose weight was considered normal, based on body mass index (BMI).
The research is not the first to suggest that those who carry a little, but not too much, extra weight tend to survive longer than people who don't.
CDC researchers found the same thing in a widely reported study published in 2005, and last month a separate group of investigators reported that overweight heart patients live longer than lean ones.
The Obesity Paradox
It is becoming known as the "obesity paradox," but this is something of a misnomer. That's because few studies have linked obesity with longer life.
Rather, the studies generally suggest that people with a BMI of 25 to 29.9 -- which is considered overweight but not obese -- have a survival advantage over people with higher or lower BMIs.
BMI, which is a measure of body fat based on a person's height and weight, is used to classify people into weight categories -- underweight, normal weight, overweight, and obese.
Based on BMI scores, a 5-foot, 5-inch adult would be considered:
- Underweight at 110 pounds or less (BMI <18.5)
- Normal weight at 111 to 149 pounds (BMI = 18.5-24.9)
- Overweight at 150 to 179 pounds (BMI = 25-29.9)
- Obese at 180 to 210 pounds (BMI = 30-34.9)
- Extremely obese at 211 pounds or more (BMI = 35 or greater)
In the newly published study, researchers used data from an ongoing Canadian national health survey to follow more than 11,000 adults from the mid-1990s to 2007.
Compared to people who fell into the normal-weight category:
- Those classified as underweight were 73% more likely to die.
- Those classified as extremely obese with BMI of 35 or greater were 36% more likely to die.
- Those classified as obese with BMI 30-34.9 had about the same risk of death.
- Those classified as overweight with BMI 25-29.9 were 17% less likely to die.
The study appears online this week in the journal Obesity.
It was conducted by researchers with Statistics Canada, McGill University, and the Kaiser Permanente Center for Health Research and funded by grants from the National Institute on Aging, the National Institute of Diabetes and Digestive and Kidney Diseases, and the Canadian Embassy.
Kaiser's David Feeny, PhD, who was a co-author of the study, tells WebMD that there are theories, but no hard evidence, to explain why carrying a few extra pounds may add a few years to your life.
Overweight People Get More Treatment
Being extremely underweight is considered a marker for poor health and frailty in older adults. Even though the researchers tried to control for this, poor health could explain why study participants who weighed the least had the biggest risk of dying.
But it is less clear why those who are overweight would have a lower risk of death than those whose weight is considered normal.
Because being overweight is a risk factor for a host of chronic diseases, including heart disease and diabetes, one theory is that their survival advantage is due to the fact that they receive more aggressive treatments to prevent these conditions.
"We tend to be quicker to prescribe statins (to lower cholesterol) and drugs to control blood pressure to patients who are overweight and we are more likely to screen them for diabetes," says weight management expert Keith Bachman, MD.
Bachman leads Kaiser's Weight Management Initiative, but he was not involved with the study.
Because the study only examined death risk, and not disease incidence or quality of life, the risk vs. benefit profile of carrying a few extra pounds is unclear, Bachman says.
"Good health is more than a BMI or a number on a scale," he says. "We know that people who choose a healthy lifestyle enjoy better health."
Feeny adds that lifestyle choices such as eating well, exercising regularly, managing stress, and treating risk factors for chronic disease may be more important for longevity than losing a few extra pounds.
"And this certainly doesn't mean that people who are normal weight should go out and binge on ice cream to gain a few pounds," he says. "The dairy industry might like that, but it would not be a good idea."