The Irish are now the second fattest people in Europe after the UK, according to a study by Organisation for Economic Co-operation and Development (OECD).
It found that one in four adults in Ireland are obese, with obesity defined as being nearly 30lbs above a normal, healthy weight.
The economic cost of excess weight is a concern for many governments.
With 30 percent of men and women clinically obese, U.S. is the fattest country in the world, followed by Mexico, Chile, New Zealand and then Britain. The slimmest country was Japan.
Franco Sassi, the OECD senior health economist who wrote the report, told the Irish Independent that lifestyles were mostly to blame.
"Food is much cheaper than in the past, in particular food that is not particularly healthy; and people are changing their lifestyles," he said.
"They have less time to prepare meals and are eating out more in restaurants."
Sassi added that the future held little hope for Ireland, adding that, "Although the data are not fully comparable, there are indications that obesity rates have increased by 40pc in Ireland in the last 10 years and there is no reason to think that growth will slow down in the near future."