The findings, presented here at the annual meeting of the American Heart Association (AHA), support recommendations to avoid trans fat as much as possible, says researcher Qi Sun, MD, of the Harvard School of Public Health.
AHA President Ray Gibbons, MD, went further. The professor of medicine at the Mayo Clinic in Rochester, Minn., says he supports a ban.
"There was no threshold below which they were safe," Sun says.
But "We saw a linear relationship: The more trans fats you consume, the worse it is for your heart," he tells WebMD.
Trans Fats in Processed Foods
The report will no doubt please New York City Mayor Michael Bloomberg, who has called for a ban on the fats in that city.
Once praised for making crunchy foods crunchier and creamy foods creamier, trans fats are in fact one of the most dangerous forms of fat.
Engineered from liquid oils through a process known as hydrogenation, they lurk in most processed foods -- including cookies, baked goods, popcorn, margarines, shortenings, crackers, doughnuts, chips, frozen waffles, and french fries. You can't get away from them.
Doctors have known for years that these fats can be damaging to the heart, but the new study is one of the first to quantify just how harmful they are, Sun says.
Also, the study was unique in that the researchers used trans fatty acid levels in red blood cells as a marker of participants' trans fat intake. Past studies used food questionnaires or food diaries, which depend upon people's often poor recall, he says.
Just 1.3 Grams Harmful
The Nurses Health Study is one of the longest-running major women's health investigations ever undertaken.
The women were divided into four groups depending on their trans fat consumption.
Those in the highest quartile -- who consumed an average of 2.0 grams of trans fats per 1,000 calories a day -- were at highest risk for heart disease.
But even those eating just 1.3 grams per 1,000 calories per day were at increased risk.
That's not much, when you consider that a typical serving of french fries has about 5 grams of trans fats, a Danish has more than 3 grams, and even microwave popcorn has 1.1 grams, Sun points out.
Eliminating such fats from your diet is a bit easier than in the past as the FDA now requires all manufacturers to list the amount of artery-clogging trans fats present in packaged foods.
But knowing how many were in that burrito you had for lunch is another story.
"We still don't know that any level of trans fats is OK," Gibbons tells WebMD. "This study buttresses arguments to get rid of them."
Gibbons notes that in 2004, Denmark enacted legislation to eliminate industrially produced trans fats from the food supply.
"While it took a lot of effort in the first few months, everyone seems happy with their food now. And they're a whole lot healthier," Gibbons says.