It seems we hear horrifying news about the dangers of trans fats every day, but just what are they, and why are they so bad?
All food oils are a combination of saturated and unsaturated fatty acids; “saturated” because double bonds are not present, “unsaturated” because they are. A saturated fatty acid has straight and rigid carbon chains that tightly fit together on top of each other to make a solid. But unsaturated fatty acids have double bonds, which are always in the cis configuration; that is, the straight, saturated portions of the chain approach and leave the double bond on the same “side,” top or bottom, so that instead of the overall chain being straight, it bends at that double bond.
Carbon chains with one double bond are slightly bent, but with two or three double bonds, the chain becomes progressively more U-shaped, flexible, losing their ability to fit well together. This lack of fit keeps them liquid; however, with liquidity comes flavor loss, decreased shelf life, and greater tendency to rancidity after being heated. To eliminate these undesirable cooking properties, the double bonds are saturated by hydrogenation so that the unsaturated fats become more like saturated fats.
The result is good for food processors but bad for consumers. Because hydrogenation is only partial, it leaves carbon chain mixtures that are both cis (bent and flexible) and trans (straight and rigid), with trans – and its solid, rigid properties – predominating. Upon absorption, these trans fats lead to the deposition of arterial plaque associated with cardiovascular disease and stoke.
Help for the consumer is on the horizon. Starting in 2006, new regulations will require food labels to provide the trans fat content if it is above 0.5%. Many food labels already have this information.