Obesity kills far more Americans than we think it does, according to a controversial new study that suggests obesity accounts of about 18 percent of all deaths in the United States - three times previous estimates.

The research, published in the American Journal of Public Health, suggests the latest government estimates soft-pedal the dangers of obesity. And the controversy over the findings show how difficult it is to calculate the costs of being overweight.

With a third of Americans overweight and another 35 percent obese, it’s not a trivial question.

The federal government has been in hot water over the issue before. In 2004 the Centers for Disease Control and Prevention slashed its estimates of obesity-related deaths from 365,000 a year to 112,000 a year, amid a battle over how it made its calculations. And a few recent studies have shown that for people over 65, having a little extra pudge may be protective.

But Ryan Masters, who did the latest study while at the Robert Wood Johnson Foundation and Columbia University, says he’s found obesity is the cause of 20 percent of deaths among women and 15 percent of men.

“We found that obesity indeed has a quite significant effect on mortality levels in the United States and estimates are actually significantly larger than prevailing wisdom has suggested,” Masters told NBC News.

“Existing literature largely indicates roughly about 5 percent of all adult deaths in the United States could be associated with overweight or obesity,” Masters says. “What we find is that between the ages of 40 and 85 … about 18 percent of all deaths that took place between 1986 and 2006 could be said to be associated with high body mass.”

Masters thinks this may get worse. There's now a whole generation of Americans who have been obese from childhood and will be obese their whole lives. The effects on them may be much worse, he predicts.

Other experts immediately questioned the way Masters made his calculations. He used data from several national health surveys that ask people, among other things, how much they weigh and how tall they are – which in turn are used to calculate body mass index (BMI) and show whether someone is overweight or obese. The data covers 20 years, from 1986 to 2006.

Then he looked at death records for the same people. “Previous research has likely underestimated obesity’s impact on US mortality,” Masters and colleagues wrote.

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“Importantly, counter to most extant research, obesity’s effect on mortality risk grows stronger with increasing age.” In 2005 and again in January, Dr. Katherine Flegal and colleagues at the National Center for Health Statistics have found that being overweight may lower your risk of death if you’re 65 or older.

“When you look at the association between weight and mortality, the association is weak,” Flegal told NBC News – although she says younger people who are obese do have a clearly higher risk of dying early.

Masters says these numbers leave out people in hospitals and nursing homes, for one thing. "From our findings, obesity actually has a very strong and substantial effect on old age mortality risk,” he says.

Why is this so hard to figure out? In part, it’s because obesity isn’t a direct cause of death.

The CDC doesn’t list obesity as a cause of death. Instead, it lists heart disease as the No. 1 cause, killing nearly 598,000 people a year, while cancer kills 575,000. Overall, nearly 2.5 million Americans died in 2010.

People who are overweight or obese are far more likely than thinner people to have heart disease, cancer, diabetes and to have strokes or heart attacks. Usually, but not always, fatter people are less fit than thinner people, and exercise can clearly protect you from death and disease.

“They didn’t account for smoking other risk factors like alcohol consumption,” says Kenneth Thorpe, a former Health and Human Services department official who is now an expert on health policy at Emory University in Atlanta. “The study doesn’t account for health insurance status, and we know that contributes to mortality rates.”

People who are obese are more likely to smoke than people who are not, Thorpe says, and they eat more unhealthful foods.

Other studies have found that the more educated people are, the less likely they are to be obese and the more they earn the thinner they are. A third of American adults who earn less than $15,000 per year are obese, compared with about a quarter of those who earn at least $50,000 per year, the non-profit Trust for America’s Health found in its “F as in Fat” report last year.

The group’s Jeff Levi says it’s important to distinguish between whether being fat causes death, or whether it’s just correlated with death. Either way, it’s bad. “Whatever the disagreements among researchers, we know that obesity is not good for your health,” Levi says.



This year's report finds Louisiana has passed Mississippi for the dubious distinction of being the state with the most obese people. It finds rates of adult Americans with a BMI of 40 or higher have grown in the past 30 years from 1.4 percent to 6.3 percent—a 350 percent increase.

“Even if the nation holds steady at the current rates, Baby Boomers—who are aging into obesity-related illnesses—and the rapidly rising numbers of extremely obese Americans are already translating into a cost crisis for the healthcare system and Medicare," Levi says.



Former Health and Human Services secretary and Wisconsin governor Tommy Thompson says this finding demonstrates why Medicare should pay for obesity treatments and why obesity should be classified as a separate disease. He applauds the American Medical Association’s decision to classify obesity as a disease.

“If we are going to get a handle on healthcare costs, obesity is front and center,” he said in a telephone interview.

“We simply must stop waiting for people to get sick and then spend infinitely more trying to make them well again," he added. "Covering obesity is a no-brainer, and we must begin behaving rationally if we are going to come to grips with rising health costs and a population that’s getting sicker.”

Jane Derenowski and Stacey Naggiar contributed to this report

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