A new study found that some American fast food contains much higher
levels of unhealthy trans fats than the same food sold in other countries.

For decades, processed food manufacturers and restaurants have used hydrogenated oil containing trans fats. This hydrogenated oil has an extended shelf life and can be reused longer for frying. But researchers determined that oil high in trans fat contributes to heart disease, and efforts are underway to eliminate these fats as much as possible.

Now a report just published in the New England Journal of Medicine tested McDonald's chicken nuggets and french fry combo meals purchased in 20 different countries. In New York City, the meal contained 10 grams of trans fat, versus 3 grams in Spain and less than 1 gram in Denmark.

The cooking oil used for the McDonald's french fries in the U.S. contained 23 percent trans fatty acids, mainly from partially hydrogenated vegetable oil. The low levels in Denmark are the result of legislation restricting the use of industrially produced trans fatty acids in food to a maximum of 2 percent.

For every 2-percent increase in the amount of calories from trans fat, the risk of heart disease increases by 36 percent, according to Walter C. Willett, chair of the Department of Nutrition at Harvard University. By replacing that same 2 percent of calories from trans fat with unsaturated fats, you can reduce the risk of heart disease by as much as 53 percent.

McDonald's claims that its cooking oils come from local suppliers and the choice is based on consumer preference. But Dr. Steen Stender, a cardiologist at Gentofte University Hospital in Denmark who worked on the study, says partially hydrogenated vegetable oils are mainly used to save money because they don't spoil and can be reused.