Trans fat is a form of unsaturated fat that has undergone the chemical process of hydrogenation to make it more saturated. While hydrogenating unsaturated fats offers certain benefits, it also raises health risks.

During hydrogenation, hydrogen is added to vegetable oil. In most cases, hydrogenation is partial, leaving the fatty acid between 5 and 60 percent saturated. The end result is known as a trans fatty acid. Partially hydrogenated vegetable oils provide about three-fourths of the total fatty acid in the U.S. diet, according to the American Heart Association.

Hydrogenation achieves two goals. First, it takes a liquid oil and makes it more stable. The more hydrogenated an oil is, the harder it is at room temperature. For instance, olive oil (which does not contain trans fat) is liquid at room temperature, while stick margarine (which does contain trans fat) is hard at room temperature. Secondly, hydrogenation extends a product’s shelf life by making it less susceptible to spoilage. 

However, hydrogenating a fat also makes it less healthy. Consuming trans fats causes an increase in both total cholesterol levels and low-density lipoprotein (LDL) – or so-called “bad” – cholesterol. Trans fats also may cause a drop in the levels of high-density lipoprotein (HDL) – or so-called “good” – cholesterol.

Hydrogenated oil is the source of most trans fatty acids. For example, margarines are created from vegetable oil. Other foods that frequently include hydrogenated fats are commercially prepared baked goods, fast foods and vegetable shortening.

Most experts do not recommend that people try to eliminate trans fats from their diets. This would be largely impractical, as these fats are found in too many foods. However, people are urged to limit their consumption of trans fats as much as possible. This can be accomplished by reading the “Nutrition Facts” section of food labels and looking for phrases such as “hydrogenated” or “partially hydrogenated.”

As of January 2006, the U.S. Food and Drug Administration (FDA) requires manufacturers to list the trans fat content of foods on packaging labels. This information also can be found on the “Nutrition Facts” label.

Trans fat is a form of unsaturated fat that has undergone a chemical process of hydrogenation to make it more saturated. This achieves two goals – it makes the fat more solid and stable at room temperature, and decreases the fat’s susceptibility to spoilage.

Fat is a nutrient essential to keeping the body properly functioning. It provides energy for the body and is a nutrient used in the production of cell membranes and in compounds called eicosanoids. These compounds are similar to hormones and help regulate blood pressure, heart rate, blood vessel constriction, blood clotting and the nervous system.

Dietary fat also helps transport fat-soluble vitamins – vitamins A, D, E and K – from food into the body’s cells. Fat promotes healthy hair and skin, protects vital organs, and insulates the body. Consuming fat also provides people with a sense of fullness, which may keep them from overeating.

However, too much fat can be bad for a person’s health. People who consume excess fat are at risk of obesity, which can contribute to many diseases and conditions, including heart disease, diabetes, gallstones, sleep apnea, osteoarthritis and cancer. A diet high in certain types of fat can also significantly raise a person’s overall cholesterol level, as well raising the level of low-density lipoprotein (LDL) cholesterol, the so-called “bad” cholesterol.

Fats are made up of glycerol (three-carbon alcohol that forms the backbone of fatty acids) and fatty acids (molecular chains of carbon, hydrogen and oxygen). They are stored in the body as triglycerides, which also circulate in the blood. There are three major types of fat: saturated fats, unsaturated fats and trans fats.  The type of a fat is dictated by the number of hydrogen atoms attached to carbon atoms in the fatty acid molecular chain.

For example, a saturated fatty acid has the maximum possible number of hydrogen atoms attached to each carbon atom. Meanwhile, an unsaturated fat has a pair of hydrogen atoms missing in the middle of the chain of carbon, hydrogen and oxygen. This leaves two carbon atoms connected by a double bond instead of a single bond. Fatty acids that have one double bond are called monounsaturated, while those that have more than one gap missing in the chain are called polyunsaturated.

Trans fats are unsaturated fats that have been hydrogenated. During hydrogenation, hydrogen is added to monounsaturated or polyunsaturated vegetable oil. In most fats, hydrogen atoms are located at double bonds on the same side of a carbon chain (cis double bonds). However, hydrogenation reconfigures some bonds so that hydrogen atoms end up on different sides of the chain. This type of configuration is known as “trans.”

In most cases, hydrogenation is partial, leaving the fat between 5 percent and 60 percent saturated. The end result is known as a trans fatty acid. The more hydrogenated an oil is, the harder it is at room temperature.

Hydrogenation is used for several reasons. It turns liquid oils into solid foods such as margarine and shortening. It also extends the shelf-life of foods such as crackers by preventing them from developing a rancid flavor and odor. Hydrogenating the oil in peanut butter helps to give the product a creamy consistency and prevents the oil from rising to the top.

However, hydrogenating a fat also makes it less healthy. Consuming trans fats causes an increase in both total cholesterol levels and LDL – or so-called “bad” – cholesterol. Trans fats also cause a drop in the levels of high-density lipoprotein (HDL) – or so-called “good” – cholesterol. The negative health impact of trans fats appears to be similar to the health risks posed by saturated fats.

Trans fat has a negative impact on health because it raises a person’s cholesterol levels. Cholesterol is a soft, waxy, fat-like substance in the blood that is mostly created in the liver from a variety of foods, especially saturated fat.

Trans fat raises the body’s levels of so-called “bad” cholesterol (low-density lipoprotein – LDL) and lowers the body’s levels of so-called “good” cholesterol (high-density lipoprotein – HDL). This can result in higher levels of cholesterol deposits on blood vessel walls, which can lead to atherosclerosis.

High levels of cholesterol are a major contributing factor to coronary artery disease. More than 12.5 million Americans have this condition and about 500,000 die of it each year, according to the National Institutes of Health (NIH).

A recent study by the Harvard School of Public Health found a strong link between consuming high levels of trans fat and increased risk of heart disease. Researchers tested the levels of trans fat in the blood of female study participants. Women with the highest levels of trans fat in their blood had three times the risk of heart disease when compared to women with the lowest levels of trans fat in their blood.

Hydrogenated oil is the source of most trans fatty acids. For example, margarines are created from vegetable oil. To create stick margarines, fatty acids are hydrogenated until the margarine has firmness greater than tub margarine or squeeze margarine (which contains more water and, sometimes, air). Other foods that frequently include hydrogenated fats are:

• Baked goods (e.g., doughnuts)
• Cakes
• Cookies
• Crackers
• Fast-food products (e.g., french fries)
• Peanut butter
• Snack foods (e.g., deep-fried chips)
• Stick margarine
• Vegetable shortening

Beef, pork, lamb, butter, milk and cheese also naturally contain small amounts of trans fatty acids. Trans fats from animal products are formed through the bacterial transformation of monounsaturated and polyunsaturated fat based from plant products in the animal’s digestive tract. Because these animal foods contain many necessary nutrients it is the trans fatty acids from processed foods and partially or completely hydrogenated oils that can be most easily eliminated from the diet.

Most experts do not recommend that people try to completely eliminate trans fats from their diets. This would be largely impractical, because these fats are found in too many foods that are important to overall nutrition (e.g., small amounts in dairy, beef and pork products). Eliminating trans fat entirely can cause inadequate intake of some nutrients and cause health risks. However, they recommend consuming as little trans fat as possible.

As of January 2006, the U.S. Food and Drug Administration (FDA) now requires manufacturers to list the trans fat content of foods on packaging labels. This information can be found on the “Nutrition Facts” label. Trans fat content does not have to be listed if the total fat in a food is less than 0.5 grams per serving and if the product makes no special claims about fat, fatty acid or cholesterol content.

The FDA estimates that by January 2009, the new labeling requirements will be responsible for preventing 600 to 1,200 heart attacks annually, including saving 250 and 500 lives.

People are urged to eat limited amounts of trans fats. This can be accomplished by reading the “Nutrition Facts” section of food labels and looking for phrases such as “hydrogenated” or “partially hydrogenated” and avoiding these foods. In addition, people should look for products that use the phrase “no trans fatty acids” or other indicators that the product does not contain trans fat.

For example, trans-free spreads are margarine-type products that have few or no trans fatty acids. Some contain fat substitutes.

In general, people should try to replace trans fats and saturated fats with unsaturated fats. These can be found in olive, canola, soybean, corn and sunflower oils. Vegetable oils (except coconut and palm kernel oils) and soft margarines are also lower in trans fat.

Other tips for reducing a person’s intake of trans fats include:

• Limit consumption of stick margarine. Instead use olive oil, canola oil, or liquid margarine. Even tub margarine – lower in trans fat – is a better choice than regular stick margarine.
  
  
• Reduce intake of fast foods, commercially prepared baked goods, snack foods and other processed foods.
  
  
• If hydrogenated foods are the only option, try to choose foods that list hydrogenated oils near the bottom of the list. The lower down the list these oils are listed, the less of the oil is contained in the product.
  
  
• Ask servers, chefs or managers at restaurants if they will prepare meals with trans-free oils.

Recently, cities such as New York have placed bans on using trans fat in restaurants. Other cities are considering such prohibitions. However, one new study has found that the type of fat frequently used to replace trans fat – a substance known as interesterified fat – may pose other health risks, such as raising blood glucose levels and depressing insulin. This can lead to diabetes. Furthermore, these new interesterified fats may depress HDL levels (the good cholesterol). However, more study is needed before any conclusions can be drawn about the potential health impact of these substitute fats.

Preparing questions in advance can help people to have more meaningful discussions with health care professionals. Patients may wish to ask their doctor or registered dietitian the following questions related to trans fat:

1. How will I know if I am eating too much trans fat?
   
   
2. What are the long-term health threats I face from trans fat?
   
   
3. What are the benefits of a diet low in trans fat?
   
   
4. Should I have my blood cholesterol levels tested?
   
   
5. Where can I find help planning a diet that is low in trans fat?
   
   
6. What are some cooking tips for reducing levels of trans fat in meals?
   
   
7. How much trans fat can I safely eat?
   
   
8. How can I ensure that my child eats a diet that has enough fat for growth while not being too high in trans fat?
   
   
9. How can I make sure my child’s school lunches are low in trans fat?
   
   
10. Can you recommend good products that use healthy ingredients as substitutes for trans fat?
    
    
11. Can you explain to me how using the new “trans fat” information on food labels can help me plan a healthier diet?
    
    
12. What products contain trans fat?