Fats are the most concentrated sources of calories, so high-fat foods are good sources of energy. You need some fat (the essential fatty acids), but for most people, it's hard not to eat too much fat. Fatty foods are everywhere, because manufacturers know that fat makes food taste good.
There are two major categories called saturated and unsaturated fats. When you take in more calories than your body needs, saturated fats raise cholesterol and increase risk for heart attacks.
Unsaturated fats are healthful as long as they are left in their natural state and not converted to partially hydrogenated fats. The "good" fats are liquid at room temperature. They are found all plants and in seafood. Unsaturated fats are further classified into omega-3, omega-6 and more, depending on their chemical structure. Omega-3 polyunsaturated fats are particularly healthful because they help to prevent clotting and swelling that increase your risk for heart attacks and cancers.
The essential fatty acids (omega-3's and omega-6's) are fats that your body cannot assemble from other fats, so you must get them in your food. Omega 6's are abundant in vegetable oils, and most people get plenty. But Omega-3's, found in seeds, whole grains and seafood, may be lacking unless you make a special effort to eat these foods. The Omega-3's are the least stable of the fats (they turn rancid quickly when exposed to air, light or heat), so they are not found in most processed foods. The healthful monounsaturated fats are found in olive oil, peanuts, canola oil and other plant sources.
Unless you burn huge amounts of calories, limit or avoid fats that are solid at room temperature – the saturated fats found in butter, meats and high-fat dairy products. We believe that everyone should try to avoid partially hydrogenated vegetable oils, found in margarine, cookies, crackers and hundreds of other processed foods (see below). Several studies link these chemically altered vegetable oils with increased rates of heart attacks and cancers.
The best fats are those you eat IN parts of plants – whole grains, beans, nuts and other seeds. When you eat corn, olives, wheat berries, soybeans, sunflower seeds or peanuts instead of their extracted oils, you get all the fiber, vitamins, minerals and phytochemicals nature packages with the fat, not just the calories.
People who need to lose weight should try to avoid all added fats (butter, margarine, oils, and processed foods made with any of these ingredients). They also need to be cautious with nuts and snack seeds, which are packed with nutrients but are so tasty that it's hard to stop with a reasonable portion size (1-2 tablespoons.)
The only way to cut back or eliminate partially hydrogenated oils (the primary source of trans fats) from your diet is to read the label of virtually every processed food you buy. Scan through the list of ingredients and if it contains the words "partially hydrogenated", put it back on the shelf.
It's much harder when you eat out, because you have no way to tell what's going on in the kitchen. Fast food restaurants and chains use a lot of pre-prepared (usuallly frozen) foods that they re-heat for you. These are often loaded with partially hydrogenated fats. You're safer at restaurants that prepare your food from scratch. Asian restaurants are good bets: they may not be low-fat, but they use liquid oils, not margarine or shortening. Most French or continental restaurants use huge amounts of butter, a concentrated source of saturated fats. This is better than trans fats, but not great if you are trying to lose weight or control cholesterol. Italian, Greek, Spanish and other Mediterranean restaurants tend to use olive oil, a more healthful choice.
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