By the time scientists understood the risks, trans fats were ubiquitous in food.
A 2003 government report estimated that 95% of manufactured cookies contained them, and pretty much all crackers. But they've been used in many other foods besides: breads, peanut butter, frozen entrees, ice cream, creamers, puddings -- and, of course, margarine.
Here are some of the fats that are now inching out the trans in those foods.
* Liquid oils from familiar sources such as corn, canola, olive and safflower. These oils are rich in unsaturated fats that do not carry the heart risks of trans or saturateds. Corn oil and cottonseed oil have been used to replace trans fats in the frying of Frito-Lay brand chips (Doritos, Tostitos, Cheetos), for example.
* Liquid oils bred or engineered for new qualities. Regular liquid vegetable oils -- though rich in heart-healthy polyunsaturated and monounsaturated fatty acids -- are also less stable to heat and air exposure. Oils from specially bred plants have a higher content of oleic acid (a more stable monounsaturated oil) and a lower content of alpha-linolenic acid (an unstable polyunsaturated oil). These newer oils have a longer shelf life and higher durability in frying. A high-oleic oil from sunflowers (called NuSun) was used to rework Goldfish crackers, Frito-Lay SunChips and trans-free Crisco, for example.
Scientists are also developing plants with greater saturated fat content -- such as soybeans with elevated levels of stearic acid, a saturated fat that does not appear as heart-unhealthy as certain other saturateds.
* Tropical oils such as palm oil (rich in a saturated fat called palmitic acid) and coconut oil (rich in another saturated fat, lauric acid) are being used in various baked goods. Palm oil was used in the reformulation of Orville Redenbacher popcorn and Oreos, for example. Often these fats are blended with liquid oils to get the right consistency.
* Blends of new and familiar liquid oils and hard, saturated fats. Some hard fats come from natural sources; others are created by the full hydrogenation of soybean, cottonseed or other oils (full hydrogenation does not produce trans fats). When the hard fats are blended with liquid oils, the result is oils with intermediate softness. Some Country Crock margarines that used to contain significant levels of trans were reformulated this way.