MadSci Network: Biochemistry

Re: How do you extract trans fats from foods?

Date: Fri Oct 24 20:10:07 2003
Posted By: Dian Dooley, , Associate Professor, Food Science and Human Nutrition, University of Hawaii at Manoa
Area of science: Biochemistry
ID: 1066179171.Bc

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 
    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' 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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