We tend to think of foods as being composed entirely of the fatty acids in their prominent groups and forms: Saturated, MUFA and PUFA. Some are aware of the different fatty acids within these groups, and most of us have learned something about the trans fat issue. Labels and articles do not include any information about the obscure fatty acids containing carbon rings and chains known as cyclic fatty acids. Some are naturally occurring, others result from refining and cooking processes. It should be briefly noted that although these complex fatty acids are normally only present in tiny amounts, the beneficial and adverse effects on our lives and health can be huge.
At any carbon bond in a fatty acid chain, the molecule kinks at a 109.5 degree angle. This happens because the pair of hydrogen atoms attached to a single bonded carbon, or the single hydrogen atom attached to a double bonded carbon, lean out away from the adjacent carbon atom bonds, pushed away by the like negative charge of the next pair or single hydrogen atom. In a saturated fatty acid, where each carbon atom is bonded to two hydrogen atoms, the adjacent kinks oppose each other, yielding a molecule that is essentially straight.
With a carbon double bond in a MUFA or PUFA, both carbons are bonded to a single hydrogen atom, and those hydrogen atoms are on the same side of the carbon chain. Hence the term “cis” from Latin which means “on the same side”. The molecule kinks twice in the same direction, yielding a molecule with two kinks at each position with a carbon double bond. The pairs of hydrogen atoms of each carbon bond rotate in relation to the single hydrogen attached to the carbon atom at each double bond, as the H2 pairs try to stay far away from that single hydrogen atom. In a three dimensional view, it looks like the molecule is describing a somewhat U-shaped spiral.
As to trans fats, literally they are transformed fats. The term “trans” is Latin for “across”. A trans fatty acid will have the individual hydrogen atoms for each linked double bonded carbon atom on opposite sides of the carbon chain. In nature, this is mostly caused by the action of bacteria in the guts of ruminant animals such as cows. Artificial means such as hydrogenation yield molecules that are now known to be absolutely deleterious to health. Simplistic diagrams meant to indicate hydrogen positions may lead one to consider that these molecules are straight, somewhat like saturated fatty acids. In an actual three dimensional view, it looks like the molecule is describing a similar somewhat U-shaped spiral as a cis molecule, but the kinks at the trans double bonds change the shape. The best generalization is that the trans molecules are not as compact as the cis version of the same molecule.
Conjugated Fatty Acids are a different critter entirely. In a regular polyunsaturated fatty acid, the location of carbon double bonds is separated by two carbon single bonds with a carbon atom between them. When conjugated, these bonds are moved closer to only have one single bond and no carbon atom between the two adjacent double bonds. Most of the buzz is about CLA’s, or Conjugated Linoleic Acid. CLA’s are based on Linoleic Acid, which has 2 carbon double bonds. Research on CLA’s is recent and still considered incomplete as to humans, yet it seems likely that some of these CLA’s have strong beneficial effects.
There are also conjugated forms of Linolenic Acid, which has three carbon double bonds. The acronym for Conjugated Linolenic Acid is CLnA. Shown below is Rumelenic Acid (RLnA) which has 3 double bonds, one of which is a trans bond. Research is really just getting started.
Another alternative to obtain low trans isomer levels in edible oils is interesterification. In this process, the fatty acid chains of two different oils are redistributed, starting a fully hydrogenated fat and a normal vegetable oil. As a result of lobbying and political wisdom, these interesterified fatty acids do not have to be reported on food labels as trans fats. The possible health issues from consuming these fats is still unclear.
One should consider that in the wide world of fats, many trans fats are among the most medicinal molecules on the planet. Many of the ingredients in age old medicines and cures are complicated cyclic trans fats. Cyclic fatty acids are the fatty acids we normally consider with varying molecular rings and/or chains attached to them.
In the body, many trans fats are just a stepping stone to other normal functional and necessary molecules. It has long been known about bacteria converting fats to trans fats in ruminant animals, such as cows. Once considered a problem, information is now pointing to some of these bacterial conversions as being ultimately beneficial. For example, some of the Conjugated Linoleic Acids (CLA’s) have been revealed to be effective in controlling many diseases and cancers. Other CLA’s are definitely bad news. The same is proving to be true about CLnA’s, or Conjugated Linolenic Acid.
It would seem a rather broad but accurate statement that basically trans fats in and of themselves do not represent a threat. Naturally produced trans fats are mostly beneficial. In general, it is the trans fats that are created by industry and those created through high temperature cooking that clearly are hazardous to your health.
Be aware that trans fats sneak into a diet. If a food contains less than .5 grams trans fat per serving, current label regulations dictate that trans fats need not be reported. Of course, the tactic is to reduce the serving size until the trans fats disappear, off the label at least. If the list of ingredients includes “shortening”, that is also code for trans fat.
The trans fatty acids listed are just a fraction of the actual isomers. There are 20 different isomers of C18:1, 8 of which are trans fats. There are 19 different isomers of C18:2, 11 of which are trans fats. There are 19 different isomers of C18:3, 13 of which are trans fats. Many are rare, some are synthetic. About half are actually found in any food. Listed here are the trans fatty acids most commonly found in food, both of natural and industrial origins. Any and all branched chain fatty acids and cyclic fatty acids present in foods from natural, industrial or cooking processes are not included in this discussion.
Just a note about molecular diagrams. Shown is an simplistic, two dimensional version that is just meant to demonstrate bond locations. Four sorts of three dimensional diagrams are used: Ball and Stick, Stick, van der Waals and Wireframe. Each is used to demonstrate different aspects of functionality of a molecule. Ball and Stick diagrams come in two flavors. The first simpler version shows bond location and the kinks from cis bonds versus trans bonds. It is useful and easy to view, but does not demonstrate an actual depiction of a molecule. The second Ball and Stick shows the actual molecular shape in 3D, which is very informative, but hard to view, especially with a complicated molecule such as a triglyceride or a cyclic fatty acid.