Unsaturated fats can be either cis fats or trans fats. While cis fats are beneficial and can promote good cholesterol, trans fats are considered harmful to cardiovascular health, especially those trans fats which come from unnatural sources (e.g., hydrogenated oils in processed foods). In November 2013, the U.S. Food and Drug Administration (FDA) said it is requiring the food industry to completely phase out artificial trans fats.
Note: Though this comparison refers to cis and trans "fats," it is more technically correct to call these "fatty acids."
|Cis Fat||Trans Fat|
|Health Effect||Generally good for health unless consumed in unreasonably high quantities.||Detrimental — lowers good cholesterol and increases the level of bad cholesterol in the body. Harmful to heart health could cause cardiac death.|
|Occurs naturally||Yes||While some natural trans fats occur in meat and dairy products, the majority of trans fats come from processed foods (i.e., hydrogenated oils).|
|Arrangement of atoms||The chains of carbon atoms are on the same side of the double bond, resulting in a kink.||Hydrogen atoms are on the opposite side of the double bonds of the carbon chain, making the fat molecule straight.|
|Melting Point||Usually low. Some cis fats are liquid at room temperature.||Usually high. Trans fats, like saturated fats, are solid at room temperature.|
While consuming cis fats in unnaturally large quantities poses a health risk, unsaturated cis fats — monounsaturated and polyunsaturated fats — generally increase the levels of good cholesterol (HDL) in the body while also decreasing bad cholesterol.
In 2002, the National Academy of Sciences concluded that trans fatty acids, whether of plant or animal origin, are nonessential and provide no benefit to human health. What's more, trans fats increase the levels of LDL (bad cholesterol) in the body, thereby increasing the risk of clogged arteries and coronary heart disease.
At least one study found that for every 2% of energy derived from trans fats, there was an associated 23% increase for cardiovascular risk. A similar study found that for every 2% of trans fat-based energy, there was a 73% greater risk of infertility in women. Numerous other studies have found links between unsaturated trans fat and obesity, as well as colon cancer. So the consumption of trans fat should be as low as possible.
One area scientists remain uncertain about is the effects of consuming naturally-occurring trans fats, which are rare but found in small quantities in meat and dairy products. The general consensus is that this type of trans fat should be avoided as much as possible, too; however, some research has suggested that natural trans fats are quite different from commercially-created trans fats and may even protect the heart. Research is ongoing.
In unsaturated fatty acids, the carbon atoms that are missing a hydrogen atom are joined by double bonds, rather than single bonds, so that each carbon atom participates in four bonds. If the hydrogen atoms are on the same side of the double bonds of the carbon chain then it is said to be in "cis" configuration. If the hydrogen atoms are on the opposite side of the double bonds of the carbon chain, then it is said to be in "trans" configuration.
The video below provides a visual explanation for cis and trans chemical structures.
A fat's chemical and physical properties change depending on the arrangement of molecules. For example, the trans fatty acid elaidic acid and naturally occurring oleic acid have the same chemical formula (C9H17C9H17O2), but they have different chemical and physical properties:
- Oleic acid has a lower melting point of 13.4 °C.
- Oleic acid is liquid at room temperature because cis molecules are loosely packed.
- Elaidic acid has a much higher melting point of 45 °C.
- Elaidic acid is solid at room temperature because trans molecules are tightly packed.
This also explains why trans fats grew in the processed food industry: they make the food last longer and decrease refrigeration requirements.
Regulation of Trans Fats
Since the mid-1950s, research has suggested there is a link between trans fats and coronary heart disease. It was not until the 1990s, however, that this link began to receive widespread notice.
In 2003 the Food and Drug Administration (FDA) issued a regulation on trans fats, allowing manufacturers to place no more than 0.5 grams of trans fats, per serving, in any given food. (This has been controversial, as many doctors and scientists agree that 0.5 grams per serving is much too lenient.) Beginning in 2006, the FDA further required manufacturers to list trans fats on nutritional labels; previously, consumers had to carefully read ingredients to know if trans fats were in food.
Since their inclusion on nutrition labels, further steps have been taken to reduce — or even ban — trans fats from foods. In November 2013, the FDA declared trans fats unsafe and took steps toward pushing manufacturers to completely remove them from processed foods. Other countries, such as Denmark, have proven it is completely possible to eliminate industrially-produced trans fats, but eliminating natural trans fats is improbable, if not impossible. Palm oil, which is heavy in saturated fat, is often used and recommended as a replacement for trans fats.
Some states, counties, and cities in the U.S. have taken additional measures to eradicate trans fats. To date, only the state of California has completely banned trans fats from restaurants.