Piling on the pounds is not only bad for health it can have a negative impact on earning power.

Just a 10 percent increase in body mass index, a measure of weight relative to height, can cut a man's real earnings by 3.3 percent and a woman's by 1.8 percent, according to economists.

Research from nine European countries shows the negative impact of weight on wages is stronger in the "oil belt" nations which include Spain, Greece, Italy and Portugal.

But in the so-called "beer belt" countries of Austria, Ireland, Denmark, Belgium and Finland gaining weight does not have a significant effect on salary.

"We find that BMI affects wages negatively in Europe, and that the size of this effect is larger for males than for females," said Giorgio Brunello, an economist at the University of Padova in Italy.

But he does not know whether it is due to discrimination against the overweight and obese or to health problems or depression that may limit their productivity.

BMI is calculated by dividing weight in kilograms by height in meters squared. A BMI between 20-25 in normal, 25-30 is pre-obese and more than 30 is obese.

Public health experts have warned that Europe is facing an obesity epidemic that will increase health costs and hamper economic development.

Up to 23 percent of men and as many as 36 percent of women in Europe are obese. It is also a growing problem in children.

Heavier European workers experience a wage penalty in the labor market, according to researchers .

The researchers said their findings are in line with the results of a recent survey of Europeans that shows Southern Europeans place a higher concern on gaining weight.