The study, published by The Lancet medical journal in Britain Thursday, covers individuals from nearly 200 countries and reveals an increase in the number of obese people from 105 million in 1975 to 641 million in 2014.
"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 senior author Professor Majid Ezzati from the School of Public Health at Imperial College London.
By 2025, 18 per cent of men and 21 per cent of women worldwide will be obese, the report predicted.
If current trends continue, the world would not meet the target of stabilising obesity rates in the next decade, Ezzati said.
The study was based on body mass index (BMI), a ratio of a person's height relative to his or her weight. A person over 30 on this scale is considered to be obese, and over 40 is considered to be severely obese.
Being obese can increase a person's risk of health conditions including diabetes, heart disease and high blood pressure.
Almost a fifth of the world's obese adults live in six high-income countries, the report said: Australia, Canada, Ireland, New Zealand, Britain, and the United States.
Island nations in Polynesia and Micronesia have the highest average BMI in the world, while East Timor, Ethiopia, and Eritrea have the lowest average BMI.
In India and Bangladesh, more than a fifth of men and a quarter of women are underweight, the researchers found.
Commenting on the findings, Professor George Davey Smith at the School of Social and Community Medicine in Bristol described the situation as "a fatter, healthier but more unequal world."
The research used data collected in over 1,600 studies, covering 19.2 million men and women aged 18 years or older, from 186 countries.
- DPA