|MadSci Network: Biochemistry|
Aloha, Sonia, Your question is unusually 'on target.' I just finished this lecture a week ago in the introductory nutrition classes that I teach here at the University of Hawai`i at Manoa. I am a Ph.D.-level nutritionist, but really enjoy teaching the non-majors course for college undergraduates. So, let me start an answer to your question by saying that you really can't 'extract trans fats' from foods. The way to avoid 'trans fats' is to avoid the foods that contain them. Now, to a more complete story. The correct term (which usually is NOT used, anyway) is 'trans fatty acids.' Fat-like compounds both in food and in your body are mainly in the form of what are called triglycerides. Simply put, these are three long-chain carbon compounds (the fatty acids) attached to a three-carbon compound called glycerol (hence the name 'triglyceride'). The fatty acids, as they come from nature in our food (both plant and animal) have the carbon chain in a kinked and zig-zag conformation (called 'cis')...and this makes the fat in the body tissues where they eventually end up less rigid, because the molecules that contain the cis-form of the fatty acids can't pack too closely together. In addition, some of the chemical bonds between the individual carbon atoms in each chain are called 'saturated' (with hydrogen atoms); some are called 'unsaturated' (could have more hydrogen atoms). You may have also heard the terms 'saturated fat,' 'monounsaturated fat,' and 'polyunsaturated fat.' The 'saturated fats' (saturated fatty acids) have all the hydrogen atoms possible around all the carbon atoms; the 'monounsaturated fats' are really fatty acids with one place in the carbon chain where more hydrogen atoms could be added; and the 'polyunsaturated fats' are really fatty acids where there are two/more places in the chain where more hydrogen atoms could be added. Where does the 'trans' come in? First off, I need to explain what hydrogenation of fats means and does. Food technologists long ago discovered that if they could chemically force hydrogen atoms into the places in the fatty acid carbon chains (in triglycerides) where there was not enough hydrogem atoms, the fat (containing the triglycerides) that resulted would be more solid at room temperature, more shelf-stable, and less susceptible to becoming rancid (from reaction with the oxygen in the air)...thus, perhaps a more acceptable form of fat (such as margarines made from vegetable oils, vegetable shortening made from vegetable oils, etc.). However, during hydrogenation, some of the by-products are more mono- and poly-unsaturated fatty acids (due to the reactions not being totally one-way...some molecular backsliding, as it were). Some of these newly created fatty acids have a slightly different structure (still zig- zag chains of carbon atoms, BUT, without the kink). This particular structure is called 'trans'...hence 'trans fats.' The downside of this process is that 'trans fats' act more like 'saturated fats' because of the straighter structure of the carbon chain...and in the body, they can create fat in tissues that is physiologically different from that created by the naturally-occuring 'cis' forms of the carbon chain. It seems to be less fluid and more rigid...not necessarily a good thing. Some scientists feel that these 'trans fats' may be related to an increased risk for some chronic diseases, such as heart disease, stroke, and maybe even cancer. Thus, now there is a federal law that will require all foods to be labeled with the 'trans fat' content...by 1 January 2006. Some food labels (potato chips, for example, that one of my nutrition students brought into class) have already begun providing this information. Foods that are sources of 'trans fats' deep-fat fried foods (such as french fries, fried fish, tempura, etc.), some breakfast cereals, cookies, crackers, coffee whiteners, and potato chips. Look on the ingredient label for the terms 'hydrogenated' or 'partially hydrogenated vegetable oils' until the Nutrition Facts labels catch up with the requirement. So, you see, you really can't remove the 'trans fats' from food...but, you can limit the use of the foods that contain them, if they are a concern to you. As a nutritionist, I would recommend that we limit the amounts of most of these foods, anyway, since they can be a source of a lot of unnecessary kilocalories and may not have a lot of other nutrients to make them worthwhile...However, I do eat potato chips, french fries, cookies, etc...I just don't eat them everyday, nor do I eat a lot of them at any one time. I hope this helps clear up the confusion. Thank you for asking such an interesting and timely question.
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