Trans fat
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A trans fatty acid (commonly shortened to trans fat) is an unsaturated fatty acid whose molecules contain trans double bonds between carbon atoms, which makes the molecules less kinked compared to those of 'cis fat'. Research suggests a correlation between diets high in trans fats and diseases like atherosclerosis and coronary heart disease. The National Academy of Sciences recommended in 2002 that dietary intake of trans fatty acids be minimized.
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Trans fats in food
Though some trans fats are found naturally (in the milk and body fat of ruminants such as cows and sheep), the majority are formed during the manufacture of processed foods (see below for details). In unprocessed foods, most unsaturated bonds in fatty acids are in the cis configuration.
Trans fat from partially hydrogenated vegetable oils has displaced natural solid fats and liquid oils in many areas.
Partial hydrogenation increases the shelf life and flavor stability of foods containing these fats. Partial hydrogenation also raises the melting point, producing a semi-solid material, which is much more desirable for use in baking than liquid oils. Partially hydrogenated vegetable oils are much less expensive than the fats originally favored by bakers, such as butter or lard. Because they are not derived from animals, there are fewer objections to their use.
In the US, snack foods, fried foods, baked goods, salad dressings, and other processed foods are likely to contain trans fats, as are vegetable shortenings and margarines. Laboratory analysis alone can determine the amount. Outside the US, trans fats have been largely phased out of retail margarines and shortenings. US food manufacturers are now also phasing out trans fats, but at present, most US margarines still have more trans fat than butter. In the 1950s advocates said that the trans fats of margarine were healthier than the saturated fats of butter, but this has been questioned. See the saturated fats page for details.
Chemistry of trans fats
Trans fatty acids are made when manufacturers add hydrogen to vegetable oil, in the presence of small amounts of catalyst metals such as nickel, palladium, platinum or cobalt -- in a process described as partial hydrogenation. If the hydrogenation process were allowed to go to completion, there would be no trans fatty acids left, but the resulting material would be too solid for practical use. A claimed exception to this is Kraft Food's new trans fat free Crisco which contains the wax-like fully hydrogenated cottonseed oil blended with liquid vegetable oils to yield a shortening much like the previous Crisco which was made from partially hydrogenated vegetable oil. However any hydrogenated or partially hydrogenated oil will contain trace amounts of the metals used in the process of hydrogenation. In a natural fatty acid, the hydrogen atoms usually form a double bond on the same side of the carbon chain. However, partial hydrogenation reconfigures most of the double bonds that do not become chemically saturated, so that the hydrogen atoms end up on different sides of the chain. This type of configuration is called trans (which means "across" in Latin). The structure of a trans unsaturated chemical bond is shown in the diagram.
Biochemistry of trans fats
Although synthetically created trans fatty acids have been a significant part of the human diet for just over 100 years, the biochemistry of trans fatty acids is poorly understood. Little is known about how trans fatty acids are incorporated into the developing fetal brain tissue, cell membranes, and arterial plaque. Some clinical studies suggest a possible association of trans fatty acids with obesity, metabolic syndrome and diabetes. It is unclear whether the naturally present trans fatty acids in beef, mutton and dairy products (created through fermentation processes in the stomach of ruminant animals) pose the same risks.
Human metabolism requires some essential fatty acids which are destroyed by the hydrogenation process. This may be a particular concern with omega-3 fatty acids, which are thought to be in short supply in the typical Western diet.
It should be noted that the destruction of some of the essential fatty acids is one of the intended goals of hydrogenation, since reducing the proportion of unsaturated fatty acids which are at risk of oxidation creates shortening that is less likely to turn rancid. For example, a typical candy bar might have a shelf life of 30 days without use of hydrogenated oils, while the same product with hydrogenated oils can last up to 18 months.
Trans fat behaves like saturated fat by raising the level of low-density lipoprotein in the blood (LDL or "bad cholesterol") which increases the risk of coronary heart disease (CHD). It has the additional effect of decreasing levels of HDL, the "good" lipoprotein which helps remove cholesterol from arteries.
The majority of clinical research reports have suggested that trans fats may be worse for the body than saturated fats; in fact, the 2002 summary statement by the Institute of Medicine on trans fatty acids concluded that there was no safe level of trans fatty acids in the human diet.
Labelling of trans fats
Consumers in the United States can find out if a food contains trans fat by looking at the ingredient list on the food label. If the ingredient list includes the words "shortening," "partially hydrogenated vegetable oil," or "hydrogenated vegetable oil," the food contains trans fat. Because ingredients are listed in descending order of predominance, smaller amounts are present when the ingredient is close to the end of the list.
Because of public awareness of the health risks of saturated fat, food companies marketed trans fat as a healthy monounsaturated fat. Whereas actual monounsaturated oils are now thought to be healthier, trans fats (which take on many of the properties of saturated fats) are much worse.
On July 9, 2003, the United States Food and Drug Administration issued a regulation requiring manufacturers to list trans fatty acids, or trans fat, on the Nutrition Facts panel of foods and some dietary supplements. This will appear below the listing of saturated fat content, which is already required to be listed.
Food manufacturers have until Jan. 1, 2006, to list trans fat on the nutrition label of items sold in the United States. The FDA estimates that by three years after that date, trans fat labeling will have prevented from 600 to 1,200 cases of coronary heart disease and 250 to 500 deaths each year. This benefit is expected to result from consumers choosing alternative foods lower in trans fatty acids as well as manufacturers reducing the amount of trans fatty acids in their products.
Canada's food regulator, Health Canada, started mandatory Nutrition Facts labels in 2003 (for gradual introduction over several years); from the beginning, they have required the listing of the amount of trans fats in the food described.
Trans fats in the news
In May 2003, a U.S. non-profit corporation filed a lawsuit against the food manufacturer Kraft Foods in an attempt to get Kraft to remove the trans fats from the Oreo cookie. The lawsuit was withdrawn when Kraft agreed to work on ways to find a substitute for the trans fat in the Oreo.
This suit was very effective at bringing the trans fat controversy to public attention.
Trans fats in history
Hydrogenation of edible oils was invented by the German chemist Wilhelm Normann, who patented the process in 1902. In 1909 Procter & Gamble in Cincinnati acquired the US rights to the Normann patent and in 1911 they began marketing Crisco, the first hydrogenated shortening, which contained a large amount of partially hydrogenated cottonseed oil. Further success came from the marketing technique of giving away free cookbooks with every recipe calling for Crisco. Hydrogenation strongly stimulated whaling, as it made it possible to stabilize whale oil for human consumption.
Ironically, public campaigns against saturated fat have caused increased consumption of trans fat. The Center for Science in the Public Interest (CSPI) campaigned against fast foods using saturated fats starting in 1984. When fast food companies replaced the saturated fat with trans fat, CSPI's campaign against them ended. CSPI defended trans fats in their 1987 Nutrition Action newsletter. By 1992 CSPI began to speak against trans fats and are currently strongly against their use.[1] (http://www.westonaprice.org/know_your_fats/cspi.html)
Legislation
Denmark became the first country to introduce laws strictly regulating the sale of many foods containing trans fats in March 2003, a move which effectively bans partially hydrogenated oils.
In November 2004, an opposition day motion seeking a similar ban was introduced by Pat Martin of the New Democratic Party of Canada, and passed through the Canadian House of Commons by an overwhelming 193-73 vote.
Naturally present trace amounts of trans fatty acids in dairy and meat products are unaffected by these bills.
External references
- Dietary fat and cholesterol: lessons from the past decade. (http://www.nin.ca/public_html/Publications/ninreview/rev302000.pdf) NIN Review. 2000 (30):1-6.
- Enig MG, Atal S, Keeney M, Sampugna J. Isomeric trans fatty acids in the U.S. diet. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2258534&dopt=Abstract). J Am Coll Nutr. 1990 Oct;9(5):471-86.
- FDA information on trans fats (http://www.fda.gov/oc/initiatives/transfat/)
- FDA HHS press release (http://www.hhs.gov/news/press/2003pres/20030709.html)
- Chemical Structure of Fats and Fatty Acids (http://www.scientificpsychic.com/fitness/fattyacids.html)
- http://www.thesoydailyclub.com/SFC/MSPproducts501.asp
- http://www.bantransfat.com/
- http://www.westonaprice.org/knowyourfats/
- http://www.cnn.com/2003/LAW/05/14/oreo.suit/
- Tips on following a low trans fat diet (http://www.mediterrasian.com)
- http://www.newscientist.com/article.ns?id=mg18424721.900de:Transfettsäuren