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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.
For the first time since the enactment of the National Labeling and Education Act of 1990, the nutrient list on food labels may be expanded to include trans-fatty acids. As the Food and Drug Administration (FDA) continues to consider amending the required nutrients to include trans-fatty acid levels, the Institute of Medicine (IOM) recently released a report that reviews the content and effects of trans-fatty acids (1). The proposed amendment and IOM report raises a concern for me as a nutrition professional and scientist: if we oversimplify the facts about trans-fatty acids,. we are misrepresenting the major foundations of our discipline of dietetics, namely, biochemistry and nutritional and food sciences.
In terms of both structure and function, all trans-fatty acids are not alike . If trans-fatty acids are grouped together as one structural entity, as is proposed for labeling by the FDA panel, there exists the possibility for mass confusion and misinformation, especially as we continue to unravel the links of each isomeric structure to physiological effects. With subtle differences in structures, 5ans-fatty acids are likely to have profoundly different physiological functions. For example, structural differences within the class known as conjugated dienoic trans-fatty acids (eg conjugated linoleic acid, CLA) may have profoundly different effects on genomic regulation, metabolic function and physiological outcomes(2). This and other findings regarding the divergent activity of various isomers of conjugated dienoic trans-fatty acids, illustrate the complexity and potential confusion of oversimplifying the nutritional messages concerning trans-fatty acids. While it is proposed that this group of trans-fatty acids not be included in the trans-fatty acids required for labeling, this decision is pending.
In terms of CLA, this group of fatty acids is a naturally occurring trans-fat found in foods from ruminant animal sources and a derivative of the fatty acid linoleic acid. The potential benefits and biological activities of this unique group of fatty acids are still being identified. Research concerning the anticarcinogenic effects of CLA has recently been extended to antiatherogenic properties, anti-diabetic properties, enhanced immune response and positive effects on energy partitioning and growth. We expect further research to find even more significant health benefits being derived from GLA. And, in fact, the American Dietetic Association identified CLA as a component contributing to the functional food properties of beef, lamb and dairy products (3). CLA cannot and should not be categorized in the same way as the man-made trans-fats found in baked goods or snack foods
Without more answers about the role of various types of trans-fatty acid isomers in health and disease, are we ready to add further confusion to the public's perception about the potentialiy large and complex role this heterogeneous group of fatty acids may play in our health? If trans-fatty acids are lumped together on a food label, or worse yet, combined with saturated fats, there are many risks to our professional identity, including our integrity as practitioners and scientists. But greater than this, we risk misinforming the public who each of us serves as practitioners, teachers, researchers, mentors and messengers. It is important that consumers make knowledgeable decisions to choose foods based on sound, peer-reviewed, replicable and definitive information. In terms of transfatty acids, it is imperative that the content of trans-fatty acids that are associated with increasing risks for cardiovascular diseases (eg elaidic and translinolelaidic acids) be distinguished from those that do not induce ather osclerotic lesions (eg CLA). Furthermore, the designation of trans-fatty acids as separate entities from saturated fatty acids is crucial for pariaying accurate and correct information to consumers. Is this too complex for the public whom we serve? In light of the alternatives, I think not.
References:
(1.) Institute of Medicine: Food and Nutrition Board. Letter report on dietary reference intakes for trans fatty acids. In: Dietary Reference Intakes for Energy, Carbohydrate, Fiber Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academy of Sciences, 2002.
(2.) Belury MA. Dietary conjugated linoleic acid in health: Physiological effects and mechanisms of action. Annu Rev Nutr. 2002;22:505-531.
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