Governments around the world should introduce new taxes on unhealthy food, and limit food and beverage advertising to children, in order to slow and eventually reverse the obesity epidemic, according to a series of papers published by the British medical journal The Lancet.

The four studies -- an exhaustive effort by an international team of researchers revealed Thursday in London -- look at obesity trends around the world, their underlying causes and misconceptions, and make recommendations about how countries like the U.S. and U.K. might slim down.

Better government policies are at the top of the list.

"Action by governments and other relevant institutions is needed to halt the obesity epidemic," the authors write, noting that taxes and limitations on advertising were previously effective in curbing tobacco use.

The researchers also say international agencies, self-regulation by the private sector, health professionals and the public at large must also contribute.

The studies found that obesity -- defined as a body-mass index greater than 30kg/m2 -- is increasing worldwide, though the stats vary greatly from country to country. Only one in 10 adult women in the Netherlands is obese, compared to one in three in the U.S. and seven out of 10 in Tonga.

Worldwide, around 2 billion adults are overweight or obese, as are 170 million children.

Obesity takes up between two per cent and six per cent of health-care costs in many countries, and in some regions including the U.S. has overtaken tobacco as the largest preventable cause of disease.

The U.S. and the U.K. have the highest obesity rates among the 34 mostly western, developed member states of the Organization for Co-operation and Development. Researchers predict that those countries will be home to 65 million and 11 million more obese adults, respectively, by 2030 if rates remain unchanged.

The studies blame the epidemic, which got going in the 1970s and 80s, on factors including sedentary lifestyles and greater consumption of cheap, high-energy food.

The researchers say rising global obesity rates pose "the toughest challenge" faced by the UN member states that are due to meet for their first high-level meeting on non-communicable diseases in September.

"The UN meeting provides a key opportunity to... seriously address the continuing global epidemic of obesity. Beyond that meeting, the test will be how well member states match their declarations with supportive funding and policies to support global actions," they wrote.