The next time you’re tempted to go get McDonald’s, think about this: just one fast food meal could raise your BMI by 0.03.

A new study from U.S. and Irish researchers has put a number on the amount of damage fast food can do to the average waistline. Researchers looked at fast food consumption and BMI in 25 high-income countries. Even after accounting for variations in activity levels, age, fruit and vegetable consumption, percent of the population living in urban areas and economic conditions in each country, the study concluded that one fast food meal was associated on average with a 0.033 increase in BMI.

BMI is a measure that combines weight and height to assess weight status and is widely used to determine whether an individual is overweight or obese. A BMI between 25 and 30 is considered overweight, while any BMI 30 or above is considered obese. Today, over two thirds of Americans have a BMI over 25.

The researchers also concluded that the average number of yearly fast food meals eaten per person increased from 26.6 in 1999 to 32.7 in 2008. The increase in fast food consumption was particularly high in Canada, Australia, Ireland and New Zealand. During the same period, average BMI increased from 25.8 to 26.4, and the researchers found a strong link between fast food consumption and BMI.

Because the study found that countries with fewer market regulations had more fast food consumption, the researchers suggested that more government regulation of the fast food industry and associated agricultural practices might help control the spread of obesity within a country.