FAT AND CHOLESTEROL: Fuel, Function, Facts and Fiction
Can fatty acids vary in their length?
In our body the length of fatty acids can vary by as much as 20 or so carbons. If a fatty acid has 4 or less carbons it is referred to as a short chain fatty acid. Furthermore, if a fatty acid chain has 6-12 or greater than 12 carbons it would be referred as a medium chain fatty acid or a long chain fatty acid, respectively. Most fatty acids in nature have an even number of carbons, however, we will certainly find fatty acids with an odd-chain length.
What are saturated and unsaturated fatty acids?
If a fatty acid is linked to glycerol the second carbon closest to the link is referred to as the alpha carbon. Meanwhile, the carbon furthest from the linkage with glycerol is called the omega carbon. You see, alpha is the first letter of the Greek alphabet while omega is the last letter. No matter how many carbons there are in your fatty acid chain these carbon atoms will always be addressed in this manner. If we were looking at a fatty acid not linked to glycerol, the alpha carbon would be the first carbon adjacent to the carbon bonded to two atoms of oxygen. Fatty acids can differ in their degree of saturation. Saturation refers to whether all of the carbons between the alpha and omega carbons are bonded to two hydrogens. If this is the case, then the carbons are saturated with hydrogen and these fatty acids would be called saturated fatty acids (SFA). However, if there are one or more points whereby adjacent carbons are only bonded to one hydrogen each, it would be an unsaturated fatty acid. This is because not all of the carbons between the omega and alpha carbons are saturated with hydrogen. By nature, when two adjacent carbons in a fatty acid are only bonded to one hydrogen each, they must bond to each other twice. This is a double bond. If a fatty acid has but one point of unsaturation or double bond, it is referred to as a monounsaturated fatty acid (MUFA). If there is more than one double bond, then it is a polyunsaturated fatty acid (PUFA).
What are trans fatty acids?
Let's take a slightly closer look at the double bond itself. If the hydrogens attached to the double bonded carbons are positioned on the same side of the double bond, it is a cis arrangement, which is by far the more prevalent way for these hydrogens to be positioned. If the hydrogens bonded to the carbons are on opposite sides of the double bond, it is referred to as a trans fatty acid. Lately there has been some interest in the presence of trans fatty acids in our diets and their impact upon health. Although a cis versus trans configuration may seem like a very minor point in regard to fatty acid design, they do impart different properties to a fatty acid. Cis double bonds cause a kinking or bending of the fatty acid, meanwhile trans double bonds do not. Thus trans double bonds are more like saturated fatty acids then unsaturated fatty acids as they are not bent like at cis double bonds.
Since fatty acids can vary in both length and saturation how can we identify specific ones?
To specify a particular fatty acid, we first count the number of carbons to determine its length, and then count the number of double bonds. If a fatty acid is 18 carbons long with one double bond we simply refer to it 18:1. Likewise, if a fatty acid is 16 carbons long with no double bonds we would refer to it as 16:0. State the length first then the number of double bonds. When a fatty acid is unsaturated we must go one step further and identify the position of the double bond(s). We can do this by counting from the omega end the number of carbons to the first carbon of the first double bond. If the first double bond appears at the 3rd carbon in it is an omega-3 fatty acid. Likewise, if the first double bond appears at the sixth or the ninth carbon the fatty acid would either be an omega-6 or omega-9 unsaturated fatty acid, respectively. When dealing with polyunsaturated fatty acids you only have to indicate the position of the first double bond. Any subsequent double bonds seem to occur in series at the third carbon from the ensuing double bond. For example, an 18:3 omega-3 fatty acid will have three double bonds positioned at the third, sixth, and ninth carbon in from the omega end.
Can different kinds of fatty acids be part of the same triglyceride molecule?
There are probably no definite rules as to the selection of fatty acids that make up a triglyceride molecule. This is to say that one triglyceride molecule may be composed of one saturated, one monounsaturated, and one polyunsaturated fatty acid, all of the same or varying lengths. The types of fatty acids found within triglyceride molecules will be strongly influenced by the nature of the plant or the animal from which you obtained the triglyceride source.