Wed Feb 2, 4:58 PM ET

Health - Reuters

LONDON (Reuters) - Life expectancy in the United States is set to drop within the next 50 years due to obesity, one of the world's top experts on the subject said on Wednesday.

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"My colleagues and I believe that within the next 50 years, life expectancy at birth will decline, and it will decline as a result of the obesity epidemic that will creep through all ages like a human tsunami," Professor Jay Olshansky of the University of Illinois said in London.

However, Olshansky declined to say by how it would drop. It is currently 80 years for females and 74.5 for males. He said his full research would be published within 6 weeks.

"There has been a dramatic increase in obesity among the younger generation and it is a storm that is approaching," he told an audience at the CASS Business School.

More than 30 percent of Americans are classified as obese, translating to around 59 million people. Being obese triples the risk of heart disease and produces a tenfold increase in the likelihood of developing diabetes.

U.S. life expectancy has increased dramatically since 1900, when the average age of death for men and women combined was 47 and most projections see life expectancy continuing to rise.

But Olshansky said the negative impact on life expectancy would likely hit when obese Americans reached middle age, which could further burden the country's state benefit system by reducing the number of people who are able to work.

Over time, however, it could reduce the pension burden if people died before reaching retirement.

According to a recent study by the Rand Corporation, if Americans continued to get fatter at current rates, by 2020 about 1 in 5 health-care dollars spent on people aged 50 to 69 could be due to obesity, 50 percent more than now.