Fast-food gets you fat faster.(file photo)

 BEIJING, April 13 (Xinhuanet) -- Researchers reported in Thursday's New England Journal of Medicine that they have found higher doses of trans fats content in US fast-food chains' products than their counterparts in other countries.

    It was estimated a few years ago that trans fats prematurely killed 30,000 to 75,000 Americans a year, though the number may have fallen due to changes some packaged-food companies made in the use of healthier oils.

    The researchers believed the main culprit to the death toll was the type of frying oil used. This partially hydrogenated vegetable oil is high in trans fats and has been injected with hydrogen to harden it and give it a longer shelf life.

    Researchers tested products from the chains' outlets in dozens of countries in 2004 and 2005, analyzing McDonald's chicken nuggets, KFC hot wings, and the two chains' fried potatoes.

    For example, they found a large fries-and-chicken-nuggets combo at a New York City McDonald's contains 10.2 grams of the trans fat, as compared to 0.33 grams in Denmark and about 3 grams in Spain, Russia and the Czech Republic.

     "I was very surprised to see a difference in trans fatty acids in these uniform products," said one of the researchers.    

    Trans fat raises bad cholesterol and lowers good cholesterol. Eating just 5 grams of it per day increases the risk of heart disease 25 percent, research shows.

    Switching to liquid vegetable oils such as canola, corn, olive or soy eliminates the trans fat, as has been done in Denmark under a 2004 law allowing only a minuscule amount of trans fat in foods.

    Experts said many U.S. restaurants still use partially hydrogenated vegetable oil to save money because it does not spoil and can be used over and over for frying.

    Michael F. Jacobson, executive director of the Center for Science in the Public Interest, said his group has petitioned the Food and Drug Administration(FDA) to drastically limit the use of trans fats and require restaurant menus to note foods containing trans fat.