Those with a body mass index, or BMI, above 40 are robbed of at least 6 1/2 years, on average, of expected life span, a study has found. And the toll in years lost rises with the degree of obesity, reaching nearly 14 years for the most obese -- those with a BMI above 55, researchers said.

The study found that the reduction in life expectancy associated with being extremely obese was similar to that seen in adults who smoke. And as a person’s obesity rises to higher levels, his or her expected life span falls below that of smokers.

The findings come from a project that aggregated the results of about 20 long-term studies on obesity conducted in the United States, Australia and Sweden. They were published Tuesday in the journal PLoS Medicine, in what is believed to be the largest study to date of the health consequences of severe obesity.

Compared with their normal-weight peers, the extremely obese are more likely to succumb early to heart disease, cancer and diabetes. For men with “class III obesity,” the rate of death attributable to heart disease and diabetes is especially elevated compared with normal-weight males. For women in the same obesity category, cancer deaths dramatically outstripped those among normal-weight women.


But premature deaths attributable to all causes, from injury to chronic lower respiratory infections, were consistently higher in those with severe obesity, the study found.

The extremely obese -- those who generally would need to lose 100 lbs. or more to attain a “normal healthy weight” -- are a fast-growing segment of the U.S. population, now representing about 6% of American adults.

The ranks of those with a BMI over 40 (for example, a 5-foot-6 person weighing 250 pounds or more) have grown fourfold since the 1980s. The population with a BMI over 50 (say, a 5-foot-10 person weighing more than 350 pounds) has grown by 10% in the same period.

Look up your BMI, a rough indicator of a body’s degree of fatness, here.


The medical costs for such patients are outsized as well, accounting for 1 in 5 healthcare dollars spent per capita in the year 2000.

The latest findings suggest that extreme obesity may be even more dangerous for men than it is for women and for younger adults compared with older ones. They come as evidence mounts that weight-loss medications, as well as diet and lifestyle counseling, work only modestly in helping the obese lose weight and keep it off.

Increasing research has shown bariatric surgery to be highly effective not only at inducing weight loss but at forestalling and reversing the health consequences of obesity. But the substantial costs of such surgery are expected to limit its widespread use.

A 2010 Kaiser Permanente study conducted in California found obesity more prevalent among African African and Latino children, even as rates of such obesity have begun to level off and even drop among non-Latino white children across the country.


Among Latino teenage boys, the rate of extreme obesity was 11.2%, and among African American teenage boys, 12% fell in the extremely obese category. A study published this year in JAMA found that 16.5% of adult African American women and 7.4% of adult Latinas had BMIs above 40.

As the extremely obese age and their ranks continue to grow, the authors of the current study said, their medical problems may reverse progress made in driving down cardiovascular disease through smoking-cessation programs and more widespread treatment of risk factors, and in driving down cancer deaths with better prevention and treatment. Cancers more prevalent among the obese are those of the breast, colon, pancreas, ovaries, kidney, esophagus, thyroid and gall bladder.

“If current global trends in obesity continue, we must expect to see substantially increased rates of mortality due to these major causes of death, as well as increasing healthcare costs,” the authors concluded.

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