The number of obese and overweight people in the developing world nearly quadrupled to almost a billion between 1980 and 2008, a think-tank report says.
There are now far more obese or overweight adults in the developing world than in richer countries, the Overseas Development Institute (ODI) said.
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The London-based institute said more than a third of all adults around the world - 1.46 billion people - were obese or overweight.
Between 1980 and 2008, the numbers of people affected in the developing world rose from 250 million to 904 million.
In the developed world, the figure rose from 321 million to 557 million.
"The growing rates of overweight and obesity in developing countries are alarming," ODI research fellow Steve Wiggins said.
"On current trends, globally, we will see a huge increase in the number of people suffering certain types of cancer, diabetes, strokes and heart attacks, putting an enormous burden on public healthcare systems."
The report said overweight and obesity rates have almost doubled in China and Mexico since 1980, and risen by a third in South Africa.
The study said the rise in obesity was down to diets changing in developing countries where incomes were rising, with people shifting away from cereals and tubers to eating more meat, fats and sugar.
The over-consumption of food, coupled with increasingly sedentary lives, was also to blame.
The report said there seemed to be little will among the public and leaders to take action on influencing diet in the future.
"Governments have focused on public awareness campaigns, but evidence shows this is not enough," said Wiggins.
"The lack of action stands in stark contrast to the concerted public actions taken to limit smoking in developed countries.
"Politicians need to be less shy about trying to influence what food ends up on our plates."