This is my field of study!
A trans-fat can be either
naturally produced or
synthetically produced in a laboratory.
The
natural trans-fat is produced mainly in bovine species, such as cows. Bacteria found in their 4-chambered stomachs biochemically convert unsaturated fat into fat molecules that have a trans-chemical formation (see attached photo).
Trans formation is far more stable than fat molecules with the cis formation (ordinary unsaturated fat). This is partly due to their shape; the straighter shape of the trans isomer leads to hydrogen intermolecular forces that make the molecule more stable. A fat molecule that is more stable will not readily become digested in the body. In fact, lipases, the enzymes that digest fats (lipids) is specific to the
cis configuration, rendering the human body unable to metabolize or remove trans fat! The human lipase enzyme is ineffective with the trans configuration, so trans fat remains in the blood stream for a much longer period of time and is more prone to arterial deposition and subsequent plaque formation. The longer a fat remains in the blood, the more likely it will become oxidized (activated) by free radicals.
The synthetically produced trans-fat, called hydrogenated fat, is far more dangerous. The process called
hydrogenation of an unsaturated fatty acid refers to the addition of hydrogen atoms to fat molecule, causing double bonds to become single ones, as carbon atoms acquire new hydrogen partners (See attached illustration). Full hydrogenation results in a molecule containing the maximum amount of hydrogen (in other words, the conversion of an unsaturated fatty acid into a saturated one).
Partial hydrogenation results in the addition of hydrogen atoms at some of the empty positions, with a corresponding reduction in the number of double bonds. Eating too much hydrogenated fat leads to high blood cholesterol -> higher chances of a heart attack.
Some foods such as beef and cheese contain small amounts of trans-fat. This does not mean it has been artificially produced, since some foods naturally contain small amounts. However, unlike hydrogenated trans-fat, natural trans-fat is metabolized similarly to saturated fats. Therefore,
although the consumption of trans-fat should be avoided entirely, it is generally safer to eat the natural form, as opposed to the hydrogenated form.
Next time you go out to purchase a jug of vegetable cooking oil, make sure it contains absolutely no trans-fat. If it does, you know that it has been hydrogenated (artificially produced) because no vegetable on earth has the capability of producing trans-fat. The same rule applies to pastries and snacks, such as chips, chocolate, or anything prepared in oil or contains oil but does not contain meat or dairy products.