Trans fat is double trouble for your heart health

Trans fat raises your "bad" (LDL) cholesterol and lowers your "good" (HDL) cholesterol. Find out more about trans fat and how to avoid it. By Mayo Clinic Staff

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.

May. 06, 2011 See more In-depth