What are trans fats?
Trans fats are unsaturated fatty acids formed when vegetable oils are processed and made more solid or into a more stable liquid. This processing is called hydrogenation. Trans fats also occur naturally in low amounts in some foods.
Trans fats from all sources provide two to four percent of total calories compared with 12 percent from saturated fat and 34 percent from total fat in the American diet. The majority of trans fats come from processed foods. About one-fifth of trans fats in the diet come from animal sources such as meats and dairy products.
What foods contain trans fats?
Trans fats are present in variable amounts in a wide range of foods, including most foods made with partially hydrogenated oils, such as baked goods and fried foods, and some margarine products. Trans fats also occur naturally in low amounts in meats and dairy products.
Why are trans fats in foods?
Trans fats form when an oil is partially hydrogenated. The process converts oils into a more stable liquid or semi-solid form. Partially hydrogenated oils are used in processed foods because they help produce high quality food products that stay fresh longer and have a more desirable texture. It is not always possible to substitute unhydrogenated oils because of differences in the way the oils work to produce acceptable food products. For example, by partially hydrogenating vegetable oils to make some margarine products, manufacturers can produce a spreadable topping that is lower in saturated fat than butter and can be used immediately upon removal from the refrigerator. Likewise, manufacturers can produce shortenings to make French fries, flaky piecrusts and crispy crackers. Partially hydrogenated oils also resist rancidity (when fats develop an off-flavor) longer than unhydrogenated oils. Foods that contain these oils must list "partially hydrogenated vegetable oil" in the ingredient statement of the food label.
Are partially hydrogenated oils used for any other reasons?
Fats and oils containing trans fats are used in place of baking and frying fats that have higher levels of saturated fats. Examples of fats with higher levels of saturated fats include lard, butter and highly saturated vegetable oils like palm, palm kernel and coconut oils. In the mid-1980s, the food industry responded to recommendations from health authorities and interest from consumers to reduce the amount of highly saturated vegetable oils along with animal fats in the food supply. The best, and in many cases the only, available alternative was to reformulate products by substituting partially hydrogenated vegetable oils for the highly saturated fats.
What is the difference between saturated fats and trans fats?
Although trans fats are unsaturated, they appear similar to saturated fats in terms of their effect on blood cholesterol levels. Some studies suggest that trans fats may raise LDL- and total blood cholesterol levels much like saturated fats do. Other studies have indicated trans fats have lesser effects on blood cholesterol levels than do saturated fats.
Will eating a diet high in trans fats increase the risk of heart disease?
The knowledge that diets high in saturated fats raise LDL-cholesterol and promote atherosclerosis has evolved through a tremendous amount of research. Additional scientific information about trans fats is needed to determine their overall role in cardiovascular disease.
Research animals fed diets high in trans fats develop almost no atherosclerosis compared to animals fed diets high in saturated fats. Human epidemiological studies have suggested a possible link between cardiovascular disease risk and high intakes of trans fats. Epidemiological studies do not prove a cause-and-effect relationship. Still, these findings generate important hypotheses that require future study.
Source: International Food Information Council, Washington, D.C.