They've shown how many years you can lop off your life by carrying around extra pounds, particularly if you're very overweight and white.
Using formulas based on a common measurement of obesity, the researchers estimate that morbidly obese young white people can reduce their life spans by eight to 13 years, depending on gender.
"It's common for people to belittle obesity as either a comic problem or a cosmetic problem. They don't see it is a real serious health problem, and this points out that it is," says study co-author David Allison, a professor of biostatistics and director of the Clinical Nutrition Research Center at the University of Alabama at Birmingham.
Allison explains he and his fellow researchers wanted to help Americans understand the risks of being significantly overweight.
"We've known with great confidence that, with all other things being equal, severe obesity results in increased mortality rate," he says. "But when I start saying things like that, it makes it sound slightly obscure. Then (researchers) use terms like 'relative risk' or 'odds ratios' and 'hazard ratios,' and I'm not sure how comprehensible they are to the public or the average physician."
Allison and his researchers examined data about American life spans that was compiled from 1971 to 1999. Then they tried to estimate how a person's body mass index affected his or her life span.
The findings appear in tomorrow's issue of the Journal of the American Medical Association.
Body mass index, or BMI, is a measure of whether a person is underweight, overweight or just right. It's calculated by dividing a person's weight in kilograms by his or her height in meters.
The researchers found that whites who lived the longest had a BMI ranging from 23 to 25; for blacks the range was 23 to 30. Being over -- or under -- those numbers could spell trouble, the researchers found.
Allison said the researchers aren't sure why blacks can be heavier than whites and not face the same risk of shorter life spans. It could have something to do with how fat is distributed in the body, he says.
That means a 5-foot-4 white person could weigh up to 145 pounds (25 BMI), while black people of the same height could go up to 174 pounds (30 BMI) without losing years off their lives, the study found.
For six-footers, whites could weigh up to 184 pounds (25 BMI) while blacks could weigh up to 221 pounds (30 BMI) and still not risk shortening their life.
Not surprisingly, morbidly obese people -- those with BMIs over 45 -- were at the highest risk of shorter life spans. White men aged 20 to 30 with a BMI over 45 lost up to 13 years of life, and white women lost as many as eight. Morbidly obese black men could shorten their life span by up to 20 years, and morbidly obese black women up to five years, according to the study.
To be morbidly obese, with a BMI of 45, a 5-foot-4 person would have to weigh 262 pounds; a six-footer would have to weigh 332 pounds.
Another study released this week also linked obesity to earlier death.
Dutch researchers examined the medical records of 3,457 people who were middle-aged in 1950 and lived in Framingham, Mass. The researchers found that non-smokers who were overweight -- with BMIs between 25 and 30 -- died three years earlier than non-smokerswho had "normal" BMIs of less than 25.
Smokers at age 40 who had BMIs above 30 -- making them obese -- lived 13 to 14 years less than their non-smoking counterparts with normal weights, according to the study. It appears in today's issue of the Annals of Internal Medicine.
The links between obesity and poor health are clear, Allison says. Being fat can boost the risk of heart disease, stroke and some kinds of cancer.
Dr. JoAnn E. Manson, a professor of epidemiology at Harvard Medical School, wrote a commentary about Allison's study. She says the findings will help doctors and politicians get a better handle on obesity's toll.
"It needs to be taken much more seriously. Obesity hasn't received the same attention that tobacco use and high cholesterol have received," she says.
Allison agrees and adds the new findings may help politicians better understand the obesity problem and perhaps devote more federal resources to fighting it.
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