Global obesity rates have doubled in the last three decades and is most widespread in Britain and the United States among the world's leading economies. If present trends continue, about half of both men and women in the United States will be obese by 2030, health experts warned.
Around 50-51 percent of American men and 45-52 percent of American women will by 2030 have a body mass index (BMI) of 30 or more, adding as many as 65 million to the country's population of obese adults, says one of the papers.
Twenty-four million of these 65 million will be older than 60.
The calculation extrapolates national estimates for 2007-08, the latest years for which data were available, when about 32 percent of American adults were obese.
Britain, too, will see a surge in obesity prevalence, from 26 percent to 41-48 percent in men, and in women from 26 percent to 35-43 percent.
By 2030, as many as 11 million more British adults will be obese, 3.3 million of them aged more than 60.
The study, led by Claire Wang of Columbia University in New York and Klim McPherson of Oxford University, says that medical costs will surge, given obesity's links with diabetes, cancer, heart disease and stroke.
"The combined medical costs associated with treatment of these preventable diseases are estimated to increase by $48-66 billion (33-46 billion euros) per year in the USA and by 1.9-2 billion pounds ($3-3.3 billion, 2.2-2.3 billion euros) per year in the UK by 2030," it says.
"Effective policies to promote healthier weight also have economic benefits."
Today, around 1.5 billion adults are overweight and a further 0.5 billion obese, with 170 million children classified as overweight or obese.
Tackling obesity accounts for between two and six percent of health-care costs in many countries and for some regions has even eclipsed tobacco as the biggest preventable cause of disease, according to the studies published in The Lancet.
They trace the pandemic to the 1970s and 80s, when a rise in food consumption per capita became coupled to a more sedentary lifestyle.