Ireland is set to become the most obese country in Europe within a decade.
Irish men already have the highest body mass index, while Irish women rank third.
Research published in the Lancet suggests that within nine years (by 2025), one in five adults worldwide will be obese. More people on the planet are now obese than underweight.
Irish men, and men in Cyprus and Malta, had the highest average male BMI in Europe at 27.8 kg/m2, the research shows.
However, report author Professor Majid Ezzati does not believe telling people they're overweight will help.
"We are much more interested in things that governments can go, and information is part of that," he said.
"However, it's really around accessibility and affordability of healthier foods, rather than just information and encouragement."
He added: "To avoid an epidemic of severe obesity, new policies that can slow down and stop the worldwide increase in body weight must be implemented quickly and rigorously evaluated, including smart food policies and improved health-care training."
Over a period of 40 years from 1975 to 2014 the number of men and women in the world classified as obese soared from 105 million to 641 million, research shows.
With each passing decade, the average person had become 1.5kg heavier.
If this trend continues, 18% of men and 21% of women worldwide will be obese by the year 2025, scientists predict. More than 6% of men and 9% of women will be severely obese and putting their health at risk.
The clinical definition of obese is a Body Mass Index (BMI), a measurement that relates weight and height, of 30 kilograms per metre squared (kg/m2).
The new analysis of BMI trends, published in The Lancet medical journal, shows that since the 1970s average BMI around the world increased from 21.7 to 24.2.
The higher figure is just below the BMI threshold of 25 where a person is considered to be "overweight".
The pooled data comes from almost 1,700 population studies and 186 countries.
In 2014 China had the largest number of obese people in the world - 43.2 million men and 46.4 million women. Chinese men accounted for 16.3% of global obesity and women 12.4%.
Next in the obesity league table was the US, with 41.7 million men and 46.1 million women. They accounted for 15.7% and 12.3% of the world's obese individuals respectively.
Despite the trend towards obesity, excessively low body weight remained a serious public health issue in the world's poorest regions, the study authors pointed out.
In southern Asia, almost a quarter of the population were still underweight, and in central and east Africa more than 15% of men and 12% of women weighed too little.
Writing in the journal, Professor George Davey Smith from the School of Social and Community Medicine at the University of Bristol in England, stressed the importance of not letting obesity divert attention away from poor nutrition.
"A focus on obesity at the expense of recognition of the substantial remaining burden of under-nutrition threatens to divert resources away from disorders that affect the poor to those that are more likely to affect the wealthier in low income countries," he warned.