Are trans fats hiding in your favorite foods? You may have no idea.

Think trans fats are a problem you no longer need to worry about? Think again, says the nonprofit Center for Science in the Public Interest (CSPI). Despite all the bad press these artificial, man-made fats have gotten over the years (and an increasingly large body of science linking them to health issues from heart disease to ovarian cancer), trans fats are still hiding in processed foods and offerings on restaurant menus, the group found.

CSPI just released a new report listing 140 foods that still contain the artery-clogging fats, some at levels as high as 9 grams per serving; groups like the American Heart Association recommend avoiding trans fats altogether, but suggest that, if you can't do that, eat no more than 2 grams max each day.

Some regional pastries sold at White Castle contained as much as 9 grams of trans fats per serving, while an order of Breaded Clam Strips at Long John Silver's had 7 grams. Celeste brand frozen pizzas were repeat mentions on the list, with pizzas containing anywhere from 3 to 5 grams per serving, and Marie Callendar's pies were right behind them at 4.5 to 5 grams of trans fats each.

Microwave and prepackaged popcorn was the worst snack food on the list. Pop Secret, Jolly Time, and Utz all contain between 3 and 5 grams of trans fats per serving. And the list revealed that people should avoid any kind of convenience breads, whether it's a Jimmy Dean Croissant Sandwich (3 grams per serving) or a Pillsbury Crescent Roll (2.5 grams per serving). In fact, nearly all of Pillsbury's prepackaged breads, cookie dough varieties, and piecrusts contain trans fats. (Click here to see the full list.)

CSPI even found that one regional brand, Mrs. Budd's Original Recipe Chicken Pot Pie, contained more partially hydrogenated oil than it did carrots or peas, but said that consumers would have no way of knowing how many of its 17 grams of fat per serving are from trans fat: The U.S. Department of Agriculture, which regulates food with meat or poultry, hasn't adopted the Food and Drug Administration's (FDA's) trans fat labeling rule requiring that trans fats be fully disclosed on labels.

But even with the FDA's labeling rule, the only way people can truly banish trans fats from their diets is by careful label reading. The agency allows amounts less than 1 gram to be labeled "0 grams per serving," so technically, companies can hide 0.5 grams of trans fats per serving—a quarter of a person's recommended daily amount—in ingredients lists alongside labels declaring the product as containing 0 grams on the trans fat line. Look for "partially hydrogenated oils" in ingredients lists to understand the type of fat in the food. And avoid them completely; they are the only sources of trans fats in the food supply.