Our understanding of the role of various fats in our diets is changing. Not so long ago, saturated fat was considered the American diet's greatest evil because too much of it can increase LDL ("bad") cholesterol and thereby increase the risk for heart disease.

While that remains true, recent research indicates that a type of fat called trans fat (hydrogenated or partially hydrogenated fatty acids) also raises LDL cholesterol. Dietary cholesterol is a third culprit that raises LDL cholesterol.

In January 2006, the Food and Drug Administration (FDA) began requiring food manufacturers to list the amount of trans fat a food contains on the label.

All fats are not equal

Fat is needed in the body as a source of energy, essential fatty acids, and to help absorb vitamins A, D, E and K, the FDA says. Fat is important for proper growth and development, as well as to maintain good health. Fat makes food taste good, gives it consistency and makes you feel full. All this is true when fat is eaten in moderation.

The kind of fat you eat is important. Fat can come from plant or animal sources. Unsaturated fats -- monounsaturated and polyunsaturated -- come from plant sources and are beneficial when eaten in moderation. Saturated fat and trans fat are not beneficial and should be limited in the diet. You should also limit the amount of dietary cholesterol that you eat.

Trans fat is found in red meat, but most trans fat comes from processed food products.   Trans fats are created when vegetable oil such as soybean or cottonseed, has hydrogen atoms added to transform the oil from a liquid into a solid. This process, called hydrogenation, is used most commonly in the manufacture of margarine or shortening. Trans fats provide no known health benefit. Their main function is to give food products a creamy consistency or crispy texture and to increase a product's shelf life.

The biggest problem with trans fats is that they're a double whammy when it comes to increasing the risk for heart disease. They boost levels of LDL cholesterol while lowering HDL ("good") cholesterol. Overall, a report by the National Academy of Sciences concluded that there is no safe level of trans fatty acids or of saturated fat, and people should limit their intake of them while consuming a nutritionally adequate diet.

Taking out trans

The U.S. Department of Agriculture's Dietary Guidelines for Americans 2005 and American Heart Association’s 2006 dietary guidelines recommend that less than 1 percent of your total daily caloric intake come from trans fats. In essence, that means to avoid trans fats, if possible. You should also continue to limit saturated fat and dietary cholesterol.

Read the labels

Look for shortening or partially hydrogenated vegetable oil on the ingredient list. Either of these ingredients is a signal that trans fats are present. The closer to the top these ingredients appear, and the more total fat listed, the more trans fat the product contains.

Be aware that products can still make claims such as "low in saturated fat" and "extra lean" and still contain trans fat. The words "trans fat free" (listed under “saturated fat” on the Nutrition Facts label means the product contains less than 0.5 gram   of trans fat per serving.

Products in which you're apt to spot partially hydrogenated oil on the Nutrition Facts label and ingredients panel include frozen French fries, ready-made cookies, crackers, doughnuts, frostings, muffins, pastries and cakes, as well as all deep-fried foods.

But they also can be found in foods where you might not expect them, such as waffles and energy and nutrition bars.

Be aware of serving sizes

Many canned and packaged products appear to be one serving but actually contain two or more servings, according to the nutrition information on the label.

Make it homemade

Bake your own cookies, cakes and breads instead of buying them. Prepare them with olive or canola oil or butter instead of margarine, which contains trans fat.

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Kids who grow quickly as toddlers or teens tend to have lower cholesterol levels as adults, new research says. A 2007 study in the Journal of Epidemiology and Community Health also found that people who become overweight after age 15 are more likely to have higher cholesterol levels.