By 2030 Europe will face an obesity crisis of "enormous proportions", according to World Health Organisation (WHO) experts.
Almost three quarters (73%) of men and 63% of women in the UK are expected to be overweight or obese that year, with a third of women categorised as obese.
But the research paints a far worse picture south of the border separating Ulster from the rest of Ireland, where being overweight is predicted to become almost universal.
In 2030, the proportion of obese and overweight men in the Irish Republic is projected to rise to 89% with a corresponding 85% of women falling into this category.
The forecast puts Irish men are at the top of an "overweight" table of 53 countries, matched only by Uzbekistan.
As far as women are concerned, Bulgaria and Belgium are predicted to have the highest proportion of overweight and obese individuals in 2030.
The so-far unpublished estimates, part of the WHO Modelling Obesity Project, were presented at the European Congress on Obesity in Prague, Czech Republic.
"Overweight" is clinically defined by a Body Mass Index (BMI) - a measure relating height and weight - of 25 to 29.9, and "obese" by a BMI of 30 and above.
For this study, the "overweight" category also included anyone who was obese.
Using these criteria, researchers looked at data from all 53 countries in the WHO European region, to compare recorded and projected figures for 2010 and 2030.
In terms of obesity alone, the estimates show a big jump for women in the Irish Republic, soaring from 23% to 57%.
The proportion of obese Irish men was expected to increase from 26% to 48% while the figure for those either overweight or obese rises from 74% to 89%.
In the UK, 36% of men and 33% of women were forecast to be obese in 2030 compared with 26% of both sexes in 2010.
For members of the population categorised as overweight or obese, levels in the UK were expected to rise from 70% to 73% for men and from 59% to 63% for women.
Other countries with projected steep rises in obesity included Greece, Spain, Sweden, Austria, and the Czech Republic.
Dr Laura Webber, from the UK Health Forum in London, who co-led the research, said: "Our study presents a worrying picture of rising obesity across Europe. Policies to reverse this trend are urgently needed. Although there is no 'silver bullet' for tackling the epidemic, governments must do more to restrict unhealthy food marketing and make healthy food more affordable.
"There are also some countries in which there were insufficient data. As these countries improve their obesity surveillance, more accurate estimates can be forecast."
Colleague Dr Joao Breda, from the WHO Regional Office for Europe in Geneva, Switzerland, said: "Although this was a forecasting exercise, and therefore data needs to be interpreted with extreme caution, it conveys two strong messages - first that the availability and quality of the data in countries needs to be improved, and second these predictions show that more needs to be done in terms of preventing and tackling overweight and obesity."
While few countries were expected to see stable or decreasing overweight and obesity rates, the Netherlands appeared to be doing better than most.
Fewer than half of Dutch men were predicted to be overweight or obese, and just 8% obese, by 2030 compared with 54% and 10% in 2010.
For Dutch women, overweight and obese rates were due to fall slightly from 44% to 43% while the level of obesity alone were expected to drop significantly from 13% to 9%.