Trans fats are a type of unsaturated fat which is uncommon in nature but can be created artificially.
Hydrocarbons are carbon atoms with hydrogen atoms attached to them. Fats (fatty acids) contain long hydrocarbon chains. The carbon atoms in the chain can be connected by single bonds or double bonds. A double carbon–carbon bond can be either across (trans) or bent (cis). In the vegetable and animal kingdoms, fatty acids generally have cis (as opposed to trans) unsaturations. In food production, liquid cis-unsaturated fats such as vegetable oils are catalytically hydrogenated to produce partially or completely saturated fats that melt at a desirable temperature (30–40 °C). Trans fats are an artificial contaminant introduced by an isomerization side reaction on the catalyst in partial hydrogenation.
Unsaturated fat is a fat molecule containing double bonds between the carbon atoms. Since the carbons are double-bonded to each other, there are fewer bonds connected to hydrogen, so there are fewer hydrogen atoms, hence 'unsaturated'. Cis and trans are terms that refer to the arrangement of the two substituent groups across the double bond. In the cis arrangement, the groups are on the same side of the double bond. In the trans arrangement, the groups are on opposite sides of the double bond. A double bond is not rotatable in ordinary conditions, but a catalyst (such as a nickel surface) can break the double bond and allow the remaining single bond to rotate.
Although trans fats are edible, consumption of trans fats increases the risk of coronary heart disease by raising levels of the lipoprotein LDL (so-called "bad cholesterol") and lowering levels of the lipoprotein HDL ("good cholesterol"). Trans fats also occur naturally in a limited number of cases: vaccenyl and conjugated linoleyl (CLA) containing trans fats occur naturally in trace amounts in meat and dairy products from ruminants. Natural and artificial trans fats are chemically different, but there is no scientific consensus about differences in their health effects.
Two Canadian studies have shown that the natural trans fat vaccenic acid, found in beef and dairy products, could actually be beneficial compared to hydrogenated vegetable shortening, or a mixture of pork lard and soy fat, by lowering total and LDL and triglyceride levels. In contrast, a study by the US Department of Agriculture showed that vaccenic acid has the same detrimental effects on LDL and HDL as industrial trans fats. In lack of recognized evidence and scientific agreement, nutritional authorities consider all trans fats as equally harmful for health and recommend that consumption of trans fats be reduced to trace amounts.
The United States FDA has issued a preliminary determination that partially hydrogenated oils (which contain trans fats) are not "generally recognized as safe", which is expected to lead to a ban on industrially produced trans fats from the American diet. In other countries, there are legal limits to trans fat content. Trans fats levels can be reduced or eliminated: alternatives are using saturated fats such as lard, palm oil or completely hydrogenated fats, interesterified fat, and alternative formulations that allow unsaturated fats to be used to replace saturated or partially hydrogenated fats. Hydrogenated oil is not a synonym for trans fat: complete hydrogenation removes all unsaturated, both cis and trans, fats.Trans fatty acids are found naturally in small quantities in some foods including beef, pork, lamb, butter, and milk, but most trans fatty acids in the diet come from hydrogenated foods. So there is good news: When the new nutrition labels go into effect Jan. 1, 2006, it will be easier to screen these fats out of your diet. Until then, look at the package's list of ingredients. Products that contain partially hydrogenated oils or vegetable shortening may contain trans fats.
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