En español | When it comes to your heart, olive oil puts the "med" in Mediterranean. Not only can it lower cholesterol levels, blood pressure, and your risk of death from heart disease, but in a new French study of people 65 and over, olive oil users slashed their risk of stroke by 41 percent.

See also: 7 foods to keep you young.

If only the facts about other fats were so clear! Remember when margarine was supposed to be better for you than butter? Then research showed it was far worse. Ditto vegetable shortening. "No wonder consumers are confused," says Dawn Jackson Blatner, R.D., a spokesperson for the American Dietetic Association.

For the record, fat is an essential part of the diet; among its other functions, it helps the body absorb nutrients from foods. But not all fats are created equal. Unsaturated fats promote health, primarily by cutting cholesterol and thus lowering heart attack risk. The two main types of these "good" fats are mono-unsaturated fats, including canola and olive oils, and polyunsaturated fats, like corn and sunflower oils. "Any oil that is liquid at room temperature is heart-smart," says Blatner.

Saturated fats such as butter and lard have the opposite effect, raising blood cholesterol, particularly " bad" LDL cholesterol, and clogging arteries.

But of all the fats, the worst for your heart are trans fats, found in vegetable shortening and stick margarine. Trans fats result when liquid oils are pumped with hydrogen to make them solid. This trick of science gives processed foods a longer shelf life — but may shorten your own. The words partially hydrogenated oil on food labels signal the presence of trans fats.

Keep in mind that even good fats are loaded with calories, so they should not exceed 25 to 35 percent of daily calories.

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