The new study, published by "The Lancet" medical journal in Britain, looked at individuals in close to 200 countries, and found that over one in eight adults are now obese - more than double the ratio in 1975.
"Over the past 40 years, we have changed from a world in which underweight prevalence was more than double that of obesity, to one in which more people are obese than underweight," said Prof. Majid Ezzati.
Of the roughly 5 billion adults recorded in 2014, 641 million were obese - more than six times the recorded number in 1975.
By 2025, the report predicted, 18 percent of men and 21 per cent of women will be obese. "There will be health consequences of magnitudes that we do not know," Ezzati told AFP news agency.
The report based its findings on the body mass index (BMI), which gauges an individual's obesity level using a ratio of the person's height relative to his or her weight. A healthy BMI lies between 18.5 and 24.9. A person over 30 is considered obese, while a person over 40 is deemed severely obese.
Nearly a fifth of the world's obese people live in six high-income countries: the US, Britain, Ireland, Australia, Canada and New Zealand. On the other side of the spectrum, East Timor, Ethiopia and Eritrea had the lowest recorded BMI numbers in the world.
blc/kms (AFP, dpa)