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Poor eating habits and a lack of exercise are two of the reasons people gain weight.

Here in the United States, the rate of obesity doubled over a span of 16 years. But the increase in obesity has had a disproportionate impact on Americans' health and longevity.

The effect of a disease — or a condition like obesity — can be tallied by a measure called quality-adjusted life years lost. It's a way of showing in one number that, for example, a diabetic or an obese person died sooner but also had years of poor health.

City College of New York professor Erica Lubetkin is one of the authors of a new study that looked at the loss of quality life years due to obesity and how that changed between 1993 and 2008.

"The rate of obesity significantly increased, in fact it was almost double, it was about 89 percent," she explained. "And with regard to the burden of disease it more than doubled, it increased over that 16 year period of time about 127 percent."

Lubetkin and her co-author based their findings on a massive collection of data, covering 3.5 million people. That large data set allowed them to analyze information for the 50 US states separately, and also to identify trends by race and gender.

For example, one question they wanted to answer was whether the loss of quality life years was due to people dying sooner — mortality — or living in poor health — morbidity.

"And for women, we found that morbidity played a greater role, but for men, mortality played a greater role," added Lubetkin.

Black women, in particular, had higher rates of obesity throughout the 16 years studied, and they paid the biggest price in terms of quality-adjusted years of life lost.

"In terms of the burden of disease, it increased for everyone, but in particular it was black women who had 31 percent more in 2008 quality-adjusted life years lost compared to black men. And compared to white women and white men, it was 50 percent higher."

Speaking via Skype, Lubetkin pointed to a clear link between the lack of exercise and the bad health consequences of obesity. US states where more people said they got no physical exercise outside work lost more quality adjusted life years.

"We can say that 50 percent of the burden of obesity can be contributed by having no leisure time physical activity," she said.

Lubetkin's paper is published in the "American Journal of Preventive Medicine."

（来源：VOA 编辑：蔡姗姗）