There are all kinds of FAT: hydrogenated fats, polyunsaturated and monounsaturated fatty acids, and fats that lower cholesterol.
What are hydrogenated fats?
During food processing, fats may undergo a chemical process called hydrogenation. "Hydrogenate" means to add hydrogen, or in the case of fatty acids, to saturate. The process changes a liquid oil, naturally high in unsaturated fatty acids, to a more solid and more saturated form. The greater the degree of hydrogenation, the more saturated the fat becomes. Many commercial products contain hydrogenated or partially hydrogenated vegetable oils.
Recent studies suggest that these fats may raise blood cholesterol. Hydrogenated fats in margarine and other fats are acceptable if the product contains liquid vegetable oil as the first ingredient and no more than 2 grams of saturated fat per tablespoon. The fatty acid content of most margarines and spreads is printed on the package or label. Liquid and soft tub margarines contain little saturated fat or trans-fat.
What are polyunsaturated and monounsaturated fatty acids?
Polyunsaturated and monounsaturated fatty acids are two types of unsaturated fatty acids. Unsaturated fats have at least one unsaturated bond -- that is, at least one place that hydrogen can be added to the molecule. They're often found in liquid oils of vegetable origin.
*Polyunsaturated oils are liquid at room temperature and in the refrigerator. They easily combine with oxygen in the air to become rancid. Common sources of polyunsaturated fats are listed in the table below.
*Monounsaturated oils are liquid at room temperature but start to solidify at refrigerator temperatures. See below for sources.
Polyunsaturated fats tend to help your body get rid of newly formed cholesterol. Thus, they keep the blood cholesterol level down and reduce cholesterol deposits in artery walls. Recent research has shown that monounsaturated fats may also help reduce blood cholesterol as long as the diet is very low in saturated fat.
Both types of unsaturated fats may help lower your blood cholesterol level when used in place of saturated fats in your diet. But you should be moderate in eating all types of fat, because fats contain more than twice the calories of either protein or carbohydrate.
Examples of Polyunsaturated fats are: sesame, soy, corn and sunflower-seed oils, nuts and seeds.
Examples of Monounsaturated fats are: olive, canola and peanut oils, and avocados.
Polyunsaturated or monounsaturated oils -- and margarines and spreads made from them -- should be used in limited amounts in place of fats with a high saturated fat content, such as butter, lard or hydrogenated shortenings. Remember to choose fats and oils that contain less than 2 grams of saturated fat per tablespoon.