BOSTON -- Starting Jan. 1, manufacturers will be required to list trans fat on food labels. But some companies have yet to comply with the new regulations.

Trans fat is fat -- and not the good kind, reported WCVB-TV in Boston.

"It increases your risk for coronary heart disease. It raises your risk for LDH cholesterol, which is the bad cholesterol," said Elisa Margolius, a registered dietitian at Newton-Wellesley Hospital in Newton, Mass.

But unlike saturated fat, trans fat has not been a Food and Drug Administration requirement for nutrition labels. That is about to change.

"As of Jan. 1, any packaged food that does not have trans fatty acid labeling should not be sold," said Alice Lichtenstein, a scientist at Tufts University.

Trans fats are created when manufacturers add hydrogen to vegetable oils to increase a food's shelf life and stabilize flavor. They are usually listed in the ingredients as partially hydrogenated oils and are most often found in packaged cookies, some margarine and anything fried.

"The products you really do want to stay away from are the commercial products -- such as the crackers, the vegetable shortening and the cookies, which do have a lot of trans fats in them," Margolius said.

Trans fats also occur naturally in meat and dairy products. Most research encourages avoiding trans fats as much as possible. But even with the new labeling, that can be tricky. Some products that claim to have zero trans fats still list partially hydrogenated oil in the ingredients.

"What that means is either there's no trans fat or there's up to .49 grams, or a little under half a gram, of trans fat per serving in that product," Lichtenstein said.

Less than half a gram of trans fat is not considered a major problem. The FDA estimates that Americans take in almost 6 grams of trans fats per day.

But dietitians agreed that less is better, especially when you sit down with a box of crackers or cookies and eat more than one serving.

"The leading research is indicating to decrease your amount as much as possible and just stay away from it," Margolius said.

Because of the new requirement, some products have changed the way they're made to cut down on trans fat levels.

For now, check the nutrition label and the ingredients for trans fats or the words "hydrogenated oil." Experts said that if you should check dietary supplements, too, to see if they have trans fat.