Trans fat is considered the worst type of fat to eat. Unlike other dietary fats, trans fats — also called trans-fatty acids — raise "bad" cholesterol and also lowers "good" cholesterol.

A diet laden with trans fats increases the risk of heart disease, the leading killer of adults. The more trans fats eaten, the greater the risk of heart and blood vessel disease.

Trans fats are so unhealthy that the U.S. Food and Drug Administration (FDA) has prohibited food manufacturers from adding the major source of artificial trans fats to foods and beverages. Several countries and several cities in the United States have limited or banned the use of trans fats.

The FDA expects that this move will prevent thousands of heart attacks and deaths every year. But, as the regulation takes effect, some products with added trans fats might still be available.

Here's some information about trans fats and how to avoid it.

Most trans fats are formed through an industrial process that adds hydrogen to vegetable oil, which causes the oil to become solid at room temperature.

This partially hydrogenated oil is inexpensive and less likely to spoil, so foods made with it have a longer shelf life. Some restaurants use partially hydrogenated vegetable oil in their deep fryers, because it doesn't have to be changed as often as do other oils.

Some meat and dairy products have a small amount of naturally occurring trans fats. However, it's not clear how these trans fats affect health.

The manufactured form of trans fat, known as partially hydrogenated oil, can be found in a variety of food products, including:

• Commercial baked goods, such as cakes, cookies and pies
• Shortening
• Microwave popcorn
• Frozen pizza
• Refrigerated dough, such as biscuits and rolls
• Fried foods, including french fries, doughnuts and fried chicken
• Nondairy coffee creamer
• Stick margarine

Doctors worry about added trans fats because they increase the risk of heart attacks, stroke and type 2 diabetes. Trans fats also have an unhealthy effect on cholesterol levels.

There are two main types of cholesterol:

• Low-density lipoprotein (LDL) cholesterol. LDL, or "bad," cholesterol can build up in the walls of arteries, making them hard and narrow.
• High-density lipoprotein (HDL) cholesterol. HDL, or "good," cholesterol picks up excess cholesterol and takes it back to the liver.

Trans fats increase LDL cholesterol and decrease HDL cholesterol, which can increase the risk of heart attack or stroke.

In the United States if a food has less than 0.5 grams of trans fats in a serving, the food label can read 0 grams trans fats.

Products made before the FDA ban of artificial trans fats might still be for sale, so check to see if a food's ingredient list says partially hydrogenated vegetable oil. If it does, that means the food contains some trans fats, even if the amount is below 0.5 grams.

These hidden trans fats can add up quickly, especially by eating several servings of different foods containing less than 0.5 grams a serving.

Experts recommend keeping the intake of trans fats, particularly the manufactured variety found in partially hydrogenated vegetable oil, as low as possible.

Foods free of trans fats aren't automatically healthy. Food makers might substitute other unhealthy ingredients for trans fats. Some of these ingredients, such as tropical oils — coconut, palm kernel and palm oils — contain a lot of saturated fat.

Saturated fat raises your total cholesterol. In a healthy diet, about 20% to 35% of total daily calories can come from fat. Try to keep saturated fat at less than 10% of total daily calories.

Monounsaturated fat — found in olive, peanut and canola oils — is a healthier option than is saturated fat. Nuts, fish and other foods containing unsaturated omega-3 fatty acids are other good choices of foods with healthy fats.