The body needs fat. It's a major energy source and also helps you absorb certain vitamins and nutrients. Only some fats are bad for you: saturated fats and trans fatty acids, or trans fats. These bad fats boost your chances of developing heart disease by increasing two of its main risk factors: LDL cholesterol and triglycerides.
But some fats are good for you, and this is the case with unsaturated fats. There are two types of unsaturated fats: polyunsaturated fats and monounsaturated fats. These good fats can help lower LDL, prevent abnormal heart rhythms, and prevent heart disease.
Saturated fats and trans fats share a physical trait: They are solid at room temperature. Think of butter, shortening, or the marbleized fat in a steak. But bad fats abound in some liquids, too, including whole milk, cream, and coconut oil. These fats drive up your total cholesterol, in particular tipping the balance toward LDL cholesterol, the destructive type that promotes the formation of blockages in the coronary arteries, the hallmark of heart disease.
Saturated fats. There are about 24 different saturated fats. Not all of them are equally bad for your health. The saturated fat found in butter, whole milk, cheese, and other dairy products increases LDL levels the most, followed by the saturated fat in beef. Curiously, the saturated fat called stearic acid, found in pure chocolate, is more like unsaturated fat in that it lowers LDL levels. Even some vegetable oils, such as palm oil and coconut oil, contain saturated fat.
Trans fats (partially hydrogenated oils). These fats occur naturally in meat, but their main dietary source is packaged baked products such as cookies, cakes, breads, and crackers, as well as fast foods and some dairy products. Trans fats were artificially created in the laboratory to provide cheap alternatives to butter. Food chemists found that they could solidify vegetable oil by heating it in the presence of hydrogen. As a result, the structure of polyunsaturated fat (a good fat) becomes more like saturated fat. Thus, solid vegetable fats such as shortening and margarine came into being. Today, trans fats are found not only in solid foods such as these, but also in foods that contain "partially hydrogenated oil."
Trans fats are even worse for you than saturated fats. Not only do they increase your LDL cholesterol, but they also reduce your beneficial HDL cholesterol. There is no safe level of trans fats.
Good fats come mainly from vegetable and fish products. They are liquid, not solid. There are two broad categories of beneficial fats: polyunsaturated and monounsaturated.
Polyunsaturated fats. When you pour liquid cooking oil in a pan, there's a good chance you're using polyunsaturated fat. Corn oil is a common example. Polyunsaturated fats are required for normal body functions, but your body can't manufacture them and so must get them from food. Polyunsaturated fats help build cell membranes, the exterior casing of each cell, and the sheaths surrounding nerves. They're vital to blood clotting, muscle contraction and relaxation, and inflammation. They reduce LDL more than they lower HDL, improving your cholesterol profile. Even better, they also lower triglycerides. There are two types of polyunsaturated fats: omega-3 (n-3) fatty acids and omega-6 (n-6) fatty acids.
Research has shown that omega-3s help prevent and even treat heart disease and stroke. Evidence also suggests they have similar benefits against autoimmune diseases such as lupus, eczema, and rheumatoid arthritis. Omega-3s come mainly from fish, but also from flaxseeds, walnuts, canola oil, and unhydrogenated soybean oil. Fatty fish such as salmon, mackerel, and sardines are especially good sources of omega-3s.
Omega-6 fatty acids also lower the risk for heart disease. High levels of linoleic acid, an omega-6, are in such vegetable oils as safflower, soybean, sunflower, walnut, and corn oils.
Monounsaturated fats. These fats should be used as much as possible along with polyunsaturated fats to replace the bad saturated fats and trans fats. Good sources of monounsaturated fats are olive oil, peanut oil, canola oil, avocados, and most nuts.
The bottom line is that "good fats" are an integral part of heart-healthy diets, especially when they replace saturated and trans fats in our diets. These healthy fats are also a good swap for some of the carbohydrates we eat.
November 2007 update