Nutritionists must love chemistry because they keep using it to create health concerns.
Fatty acids are classified as saturated - if their structural backbone of carbons has only carbon-carbon single bonds;
- they are classified as monounsaturated if they have one carbon-carbon double bond and single bonds holding the other carbons together;
- and polyunsaturated - if they have two or more carbon-carbon double bonds (again the other carbons are bonded to each other with single bonds).
Carbon has 4 electrons in its outermost shell. It typically bonds to other atoms with electrons that it can share.
Typically, these bonds are C-H; C-C; etc.
Carbon is most stable in a bonded relationship when it has 8 electrons (4 it provides and 4 from other sources). A bond involving carbon with some other atom represents a sharing of two electrons.
In the world of polyunsaturated fatty acids (oils with two or more carbon-carbon double bonds), there is a process called HYDROGENATION that can be used to add hydrogens across the carbon-carbon double bonds to create carbon-carbon single bonds.
Hydrogenation makes the oils more saturated and hence more solid. Another point of information is that polyunsaturated fatty acids, since they have a number of double bonds, tend to be more easily broken apart into carbon fragments when they are used in frying.
Another very important point is that all fatty acids in our bodies are synthesized from two carbon fragment molecules called acetyl coenzyme A (acetyl CoA).
Our cells can combine two of these units to create a 4 carbon unit; then add another acetyl CoA to create a 6 carbon unit; and so on until an 18 to 24 carbon unit (a fatty acid) is created.
Likewise, when we break down a 24 carbon unit fatty acid - we take away a two carbon fragment followed by another and another, etc.
Hence a 24 carbon fatty acid can be broken down into 12 acetyl CoA's (each with 2 carbons). The importance of this is that if we consume an 8 carbon polyunsaturated fatty acid with a configuration of double bonds between carbons 2-3; 4-5; and 6-7. This consumed polyunsaturated fatty acid would be a form that typically is present when a cell is directed to break it down. Since this is not the direction - the cell typically uses hydrogenation to add hydrogens across these double bonds and essentially creates a saturated fatty acid.
If you have followed along to this point let me illustrate the fatty acid in question.
The consumed fatty acid looks like this: C-C=C-C=C-C=C-C. The cell would add hydrogens across these double bonds and create the following structure: C-C-C-C-C-C-C-C.
The reader must note I have not included the hydrogens also attached to the carbons for simplicity. The point being that if we consume polyunsaturated fatty acids in a form that signal "a breakdown form in the cell", the cell will hydrogenate it.
Now, not all polyunsaturated fatty acids are of this structural backbone. Say we consume one with a structure of: C-C-C=C-C-C=C-C-C.
None of the double bonds if broken in the cell will create a two carbon fragment. Hence, the cell will not add hydrogens across the double bonds, and will simply store it within triglycerides.
Back to trans fatty acids.
Fatty acids with at least one double bond can form two stereoisomers referred to as cis and trans forms.
Double Bond in Cis form Double Bond in Trans form
R R R H
C = C C = C
H H H R
R = some group of any carbon length
H = hydrogen
Note in Cis form the two R's are on same side of double bond as are the H's ( cis = same)
Note in Trans form the R's are across from each other as are the H's (Trans = across).
Thus a double bond in a fatty acid can exist in both cis and trans forms. Typically the cis form has a "u" or bend shape while the trans form is typically linear.
Each food has concentrations of both cis and trans forms - naturally occurring.
percentage trans fatty acids
Milk and cheese 18.8
Butter 5.9
Eggs 0.9
Meat and Meat products 10.3
Trans fatty acids are polyunsaturated fatty acids with unusual shapes due to hydrogenation. The addition of these trans fatty acids to food products has caused concern among some nutritionists. Many researchers estimate that trans fatty acids carry a risk to health of the heart and arteries between that of saturated and unsaturated fatty acids.
Common food sources of trans fatty acids include: most margarines, shortenings, and peanut butters; fast foods, salad dressings and mayonnaise; biscuits, rolls, cakes, crackers; corn snacks and chips; cookies, doughnuts, french fries and fried chicken.
Percentage of trans fatty acids resulting from hydrogenation.
Oils and fat 35.5
Biscuits and cakes 16.5
More data on percent of trans fatty acids can be found at link below.
