A “tsunami of obesity” is unfurling across the world, resulting in a near-doubling of the numbers of dangerously overweight adults since 1980, doctors warned last Friday.

More than half a billion men and women – nearly one in nine of all adults – are clinically obese, according to research by a team from Imperial College London, Harvard and the World Health Organisation (WHO).

In 2008, the latest year for which statistics were available, nearly one woman in seven and one man in 10 were obese, it found.

Being too fat causes three million premature deaths each year from heart disease, diabetes, cancers and other disorders, according to the WHO.

The researchers described the tableau as “a population emergency.”

“(It) will cost tens of millions of preventable deaths unless rapid and widespread actions are taken by governments and health-care systems worldwide,” said the report, published by The Lancet.

The problem has been most prevalent in rich nations, rising most in the US, followed by New Zealand and Australia for women, and Britain and Australia for men.

But many developing countries, especially in the Middle East and in rapidly urbanising areas, are catching up.

Global obesity rates more than doubled for men, from 4.8 per cent of male adults in 1980 to 9.8 per cent in 2008. For women, the corresponding jump was from 7.9 to 13.8 per cent.

The standard for assessing weight is the body-mass index (BMI), in which one’s weight in kilos is divided by the square of one’s height in metres.

A BMI of 25 to 30 corresponds to being overweight, while above 30 is obese.

In Europe, women in Russia and Moldova were at the upper end of the scale with BMIs of 27.2 and 27.1, while the heftiest men on the continent resided in the Czech Republic and Ireland.