By Mayo Clinic News Network

When it comes to fat, trans fat is considered by some doctors to be the worst type of fat. Unlike other fats, trans fat — also called trans-fatty acids — both raises your "bad" (LDL) cholesterol and lowers your "good" (HDL) cholesterol.

A high LDL cholesterol level in combination with a low HDL cholesterol level increases your risk of heart disease, the leading killer of men and women. Here's some information about trans fat and how to avoid it.

What is trans fat?

Trans fat is made by adding hydrogen to vegetable oil through a process called hydrogenation, which makes the oil less likely to spoil. Using trans fats in the manufacturing of foods helps foods stay fresh longer, have a longer shelf life and have a less greasy feel.

Scientists aren't sure exactly why, but the addition of hydrogen to oil increases your cholesterol more than do other types of fats. It's thought that adding hydrogen to oil makes the oil more difficult to digest, and your body recognizes trans fats as saturated fats.

Trans fat in your food

Commercial baked goods — such as crackers, cookies and cakes — and many fried foods, such as doughnuts and french fries — may contain trans fats. Shortenings and some margarines can be high in trans fat.

Trans fat used to be more common, but in recent years food manufacturers have used it less because of concerns over the health effects of trans fat. Food manufacturers in the United States and many other countries list the trans fat content on nutrition labels.

However, you should be aware of what nutritional labels really mean when it comes to trans fat. For example, in the United States if a food has less than 0.5 grams of trans fat per serving, the food label can read 0 grams trans fat. Though that's a small amount of trans fat, if you eat multiple servings of foods with less than 0.5 grams of trans fat, you could exceed recommended limits.

Reading food labels

How do you know whether food contains trans fat? Look for the words "partially hydrogenated" vegetable oil. That's another term for trans fat.

It sounds counterintuitive, but "fully" or "completely" hydrogenated oil doesn't contain trans fat. Unlike partially hydrogenated oil, the process used to make fully or completely hydrogenated oil doesn't result in trans-fatty acids. However, if the label says just "hydrogenated" vegetable oil, it could mean the oil contains some trans fat.

Although small amounts of trans fat occur naturally in some meat and dairy products, it's the trans fats in processed foods that seem to be more harmful.

Trans fat and cholesterol

Doctors worry about trans fat because of its unhealthy effect on your cholesterol levels — increasing your LDL and decreasing your HDL cholesterol. There are two main types of cholesterol:

  • Low-density lipoprotein (LDL). LDL, or "bad," cholesterol transports cholesterol throughout your body. LDL cholesterol, when elevated, builds up in the walls of your arteries, making them hard and narrow.
  • High-density lipoprotein (HDL). HDL, or "good," cholesterol picks up excess cholesterol and takes it back to your liver.

A high LDL cholesterol level is a major risk factor for heart disease. If your LDL is too high, over time, it can cause atherosclerosis, a dangerous accumulation of fatty deposits on the walls of your arteries. These deposits — called plaques — can reduce blood flow through your arteries. If the arteries that supply your heart with blood (coronary arteries) are affected, you may have chest pain and other symptoms of coronary artery disease.

If plaques tear or rupture, a blood clot may form — blocking the flow of blood or breaking free and plugging an artery downstream. If blood flow to part of your heart stops, you'll have a heart attack. If blood flow to part of your brain stops, a stroke occurs.

Other effects of trans fat

Doctors are most concerned about the effect of trans fat on cholesterol. However, trans fat has also been shown to have some other harmful effects:

  • Increases triglycerides. Triglycerides are a type of fat found in your blood. A high triglyceride level may contribute to hardening of the arteries (atherosclerosis) or thickening of the artery walls — which increases the risk of stroke, diabetes, heart attack and heart disease.
  • Increases Lp(a) lipoprotein. Lp(a) is a type of LDL cholesterol found in varying levels in your blood, depending on your genetic makeup. Trans fats make Lp(a) into smaller and denser lipid particles, which promotes a buildup of plaques in your arteries.
  • Causes more inflammation. Trans fat may increase inflammation, which is a process by which your body responds to injury. It's thought that inflammation plays a key role in the formation of fatty blockages in heart blood vessels. Trans fat appears to damage the cells lining blood vessels, leading to inflammation.

Avoiding trans fat

The good news is trans fat is showing up less in food, especially food on grocery store shelves. If you eat out a lot, however, be aware that some restaurants continue to use trans fat. Trans fat is sometimes a part of the oil restaurants use to fry food. A large serving of french fries at some restaurants can contain 5 grams or more of trans fat.

How much trans fat you can safely consume is debatable. However, there's no question you should limit trans fat, according to the Food and Drug Administration and the American Heart Association (AHA).


What should you eat?


