A trans fatty acid (commonly shortened to trans fat) is an unsaturated fatty acid molecule that contains a trans double bond between carbon atoms, which makes the molecule less kinked compared to '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.

Trans fats in food

Though a negligible amount of trans fats are found naturally (in mostly animal foods and early clinical research shows an important role of these naturally occurring trans fatty acids in the immune system), the vast 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.

Snack foods, fried foods, baked goods, salad dressings, and other processed foods are therefore likely to contain trans fats, as are vegetable shortenings and margarines. Laboratory analysis alone can determine the amount.

Though some newer variants differ, most margarines have much more trans fat than butter. In the 1950s advocates said that the trans fats of margarine were healthier than the saturated fats of butter. Some say the theory that saturated fats are unhealthy is wrong anyway. See the saturated fats page for details.

A trans configuration of hydrogen atoms

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. Usually the hydrogen atoms at a double bond in a natural fatty acid are positioned 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 artificially 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 trace amounts of naturally present trans fatty acids in some meats and dairy products (created especially through fermentation processes in the gut 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

William Procter and James Gamble started the company Procter & Gamble and hired chemist E.C. Kayser and developed the process to hydrogenate cottonseed oil. The initial purpose was to make a cheaper substance to make candles than the expensive animal fats in use at the time. Electricity began to diminish the candle market, and since the product looked like lard, they began selling it as a food. This product became known as Crisco. Further success came from the marketing technique of giving away free cookbooks with every recipe calling for Crisco.

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]

While saturated fats have been consumed in significant quantities by many healthy and long-lived societies without any heart problems for centuries, trans fat products are less than a century old.

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.

An opposition day motion introduced by Pat Martin of the New Democratic Party of Canada in November 2004 seeking a similar ban passed through the Canadian House of Commons, by an overwhelming 193-73, a rare event given the state of the minority parliament.

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. NIN Review. 2000 (30):1-6.
• Enig MG, Atal S, Keeney M, Sampugna J. Isomeric trans fatty acids in the U.S. diet.. J Am Coll Nutr. 1990 Oct;9(5):471-86.
• FDA information on trans fats
• FDA HHS press release
• Chemical Structure of Fats and Fatty Acids
• 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.newscientist.com/article.ns?id=mg18424721.900