All foods contain a mixture of the three different types of fats: saturated, polyunsaturated and monounsaturated. There are no foods that contain only one type. They contain the three types of fat in varying proportions, and the type that occurs in the largest percentage is used to name that fat. For example, olive oil is called a monounsaturated fat because it contains more monounsaturated fat than polyunsaturated or saturated, but it has some of all three types.SATURATED FATS: These fats are solid at room temperature. When you take in more calories than your body needs, saturated fats raise cholesterol and increase risk for heart attacks. Large amounts of saturated fats are found in butter, meats and high-fat dairy products.
MONOUNSATURATED FATS are liquid at room temperature. They are found in all food sources of fats, but particularly rich sources include olives, almonds and other seeds. Before the bad LDL cholesterol can form plaques in arteries, it must first be converted to oxidized LDL. Monounsaturated fats are thought to stabilize the bad LDL cholesterol and make it less likely to form plaques in arteries. Recent studies suggest that their heart-health benefits may come from antioxidants and other phytochemicals found in the seeds as well.
POLYUNSATURATED FATS are healthful as long as they are left in their natural state, which is liquid at room temperature, and not converted to the more solid partially hydrogenated oils (see below). Polyunsaturated fats include the essential fatty acids (omega-3’s and omega-6’s) , which your body cannot assemble from other fats, so you must get them in your food. Omega 6’s are abundant in vegetable oils and processed foods, and most people get plenty. Omega-3’s are found only in whole grains, beans, nuts and other seeds, and in seafood; you may not get enough unless you make a special effort to eat these foods. 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. Omega-3's help to prevent clotting and inflammation, so they decrease your risk for heart attacks and strokes.
PARTIALLY HYDROGENATED OILS contain trans fats. Polyunsaturated fats in vegetable oils are healthful if they are left in the vegetables. Removing fats from vegetables shortens their shelf life. To keep them from turning rancid, they are either processed with heat, which destroys the very unstable essential omega-3 fatty acids; or, even worse, they are converted into harmful partially hydrogenated oils. Hydrogen atoms are added to replace the unsaturated double bonds between carbons, to create a very stable, more solid fat that is similar to saturated fat but has a different chemical structure.
The trans fats in partially hydrogenated oils increase risk for heart attacks by lowering blood levels of the good HDL cholesterol, raising levels of the bad LDL cholesterol and Lp(a), and blocking arachidonic acid to cause clotting. Partially hydrogenated fats also lower blood levels of the inflammation-reducing omega-3 fatty acids.
Partially hydrogenated fats are the principal fat in many prepared foods, such a french fries, doughnuts, frozen meals, cookies and crackers. Some major food producers are responding to public pressure to get trans fats out of our food supply, but they are still widely used. I believe that everyone should keep intake of partially hydrogenated fats (trans fats)in your daily diet as close to zero as possible.
Read more about the good fats and bad fats in The Good Food Book; it's free -- see the link below.
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Dr. Gabe Mirkin has been a radio talk show host for 25 years and practicing physician for more than 40 years; he is board certified in four specialties, including sports medicine. Read or listen to hundreds of his fitness and health reports at http://www.DrMirkin.com
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