By Lea Ann Holzmeister, RD, CDE | September 21, 2007 12:00 am
Fat plays many important roles in a healthful diet. It provides energy and essential fatty acids, which are necessary for good health. It helps to maintain healthy skin and to regulate cholesterol metabolism, and it contributes to substances in the body called prostaglandins, which regulate other body processes. Dietary fat aids in the absorption of the fat-soluble vitamins A, D, E, and K, and it helps to satisfy the appetite by making you feel full after eating.
Despite all the important functions of fat, there is clear evidence that a diet that is too high in fat can contribute to many health problems, including some types of cancer, heart disease, diabetes, and obesity. High intakes of saturated fat, trans fat, and cholesterol increase the risk of unhealthy blood fat levels. In general, a healthy amount of fat in the diet ranges between 20% and 35% of total calories. Consuming more than 35% of total calories as fat can lead to a high intake of saturated fat and can also make it difficult to keep calorie intake at a desirable level.
Being selective about the types of fat you eat is important for your heart health. Saturated fat and trans fat raise low-density lipoprotein (LDL, or “bad”) cholesterol levels in the blood, which raises the risk of developing heart disease. Trans fat additionally decreases high-density lipoprotein (HDL, or “good”) cholesterol levels.
The American Diabetes Association’s (ADA) latest nutrition recommendations advise getting less than 7% of calories from saturated fat and minimizing intake of trans fat. For a person who consumes 1500 calories per day, 7% of calories from saturated fat is less than 12 grams of saturated fat per day. (When converting grams of fat into calories, remember that each gram of fat contains 9 calories. Therefore, 1500 x 7% = 105 calories. 105 ÷ 9 = 12 grams.) Cooking oils contain varying amounts of saturated fat, but because they are not hydrogenated during processing, they do not contain trans fat.
Dietary cholesterol is a fatlike substance found only in foods of animal origin. It, too, can raise LDL cholesterol levels, which is why the ADA recommends that people with diabetes limit their dietary cholesterol intake to less than 200 milligrams per day. However, all of the cooking oils reviewed in this article are vegetable oils, so they do not contain cholesterol.
The types of fat that appear to be good for heart health are monounsaturated fats, polyunsaturated fats, and a type of polyunsaturated fat called omega-3 fatty acids. Plant sources high in monounsaturated fats include most nuts and certain vegetable oils, including canola oil, olive oil, high-oleic safflower oil, and high-oleic sunflower oil. Plant sources high in polyunsaturated fats include walnuts, flaxseed, and some vegetable oils, including soybean oil, corn oil, regular safflower oil, and canola oil.
Omega-3 fatty acids are found primarily in seafood, especially higher-fat, cold-water fish such as mackerel, salmon, sardines, albacore tuna, and lake trout. However, there are some plant-based products that are high in omega-3 fatty acids, including soybean oil, canola oil, flaxseeds, and walnuts. Omega-3 fatty acids lower the risk of heart attacks by preventing blood platelets from clotting and sticking to artery walls.
Most cooking oils naturally provide 10% to 20% of the Daily Value for vitamin E. Some products, such as Hollywood Enriched Expeller Pressed Safflower Oil, contain added vitamin E and may provide up to 30% of the Daily Value. Check the Nutrition Facts panel on the label for an oil’s vitamin content.
People have been extracting vegetable oil from plant materials for thousands of years. The very earliest methods of pressing vegetable matter probably yielded at best 10% of the available oil. More modern methods involving chemical solvent extraction can extract all but 1% to 2% of the oil.
Most cooking oil contains 100% vegetable oil, with no additives or preservatives. The oil most commonly comes from the seeds of the plant (in the case of sunflower, palm kernel, grapeseed, sesame, soybean, cottonseed, and safflower oils) or the nuts (in the case of walnut, peanut, hazelnut, and almond oils). Several cooking oils are derived from the flesh of the fruit of the plant. For example, coconut oil comes from the white meat of the coconut, palm oil from the pulp of the palm fruit, and olive oil from the flesh of fresh olives.
Some cooking oils, including olive, peanut, and some coconut and sunflower oils, are expeller-pressed, meaning that the plant part from which oil is derived is crushed and pressed to produce the oil. The oil is then left crude or refined. Crude oils may have a cloudy appearance and are more flavorful, but they have a shorter shelf life than refined products. Some manufacturers label their products cold-pressed to indicate that the plant materials were not heated during oil extraction. However, this label term is largely unregulated and cannot always be relied on to mean that the oil was never exposed to high heat.
Most cooking oils are extracted from ground plant material with a chemical solvent. After extraction, the oil is cleaned, refined, and filtered and/or distilled. This process produces a bland, clear oil.
All fats, including cooking oils, are a mixture of saturated, monounsaturated, and polyunsaturated fatty acids in varying proportions. There is no such thing as a saturated-fat-free oil or one that contains only polyunsaturated or monounsaturated fat.
Fatty acids, the units that make up fats, differ primarily in the amount of hydrogen they contain. Saturated fatty acids contain the most hydrogen, while monounsaturated and polyunsaturated fatty acids contain less hydrogen. A fat’s consistency at room temperature is a clue to its fatty acid makeup: Vegetable oils that are liquid at room temperature contain high amounts of unsaturated fats and little saturated fat. Coconut, palm, and palm kernel oil, which have more saturated fat, are solid at room temperature. Stick margarine that is made with hydrogenated fats and butter, which is high in saturated fat, are solid at room temperature.
All cooking oils will oxidize and therefore hydrogenate to a small degree if repeatedly heated to a very high temperature, as is done in commercial frying. This means the fats become more saturated and start to contain some trans fat over time. However, it is almost impossible to oxidize fat to this degree in home cooking.
Cooking oils differ in their “smoke point,” or the temperature to which they can be heated before they smoke, discolor, and break down. At the smoke point, the oil not only smokes and begins to emit unpleasant odors, but it also imparts unsavory flavors onto the food. Reaching the smoke point means you are approaching the “flash point,” which is when the oil can erupt into flames.
Factors that will lower the smoke point of an oil include the number of times an oil has been used, the length of time it has been heated, any exposure to light, oxygen, and high temperatures during storage, and the presence of substances such as salt or food particles in the oil. Cooking oils with a high smoke point can be heated to high temperatures before burning. Knowing a cooking oil’s smoke point gives you some indication of whether it is good for cooking and frying. In general, the best oils for high-temperature cooking methods such as deep-fat frying are safflower, sunflower, peanut, soy, and canola oils.
While all cooking oils are a mixture of types of fatty acids, most can be categorized as being high in one of the three types of fatty acids: monounsaturated fat, polyunsaturated fat, or saturated fat. The following oils are high in monounsaturated fat.
Almond oil. This nut oil is best used in cold dishes to avoid destroying its delicate flavor.
Avocado oil. This is a light, nutty oil that is best used in salad dressings.
Canola oil. This oil is extracted from rapeseeds (a plant in the mustard family). It is versatile, neutral tasting, high in omega-3 fatty acids, and very low in saturated fat. It can be used in salad dressings or in cooking.
Hazelnut oil. This fragrant, nutty oil is often pressed from roasted hazelnuts and is best used in cold dishes such as salad dressings and sauces to avoid destroying its delicate flavor.
Olive oil. The oils extracted from olives range from light amber to green in color and from bland to very strong and even spicy in flavor. Olive oil can be graded or classified as virgin, refined, or pure. Virgin or extra-virgin means the oil has been produced by the use of physical means (expeller-pressed) and there has been no chemical treatment during processing, resulting in a full-flavored oil. Extra-virgin oil is the highest grade and comes from the first pressing of the olives. Refined means the oil has been chemically treated to neutralize strong tastes and acids. Pure olive oil and products simply labeled “olive oil” may be a combination of virgin and refined oil. Unfiltered means the oil contains small particles of olive flesh. Light refers to flavorless or refined olive oil; it is not lower in calories. Olive oil blends are mixtures of olive oil and other, often less expensive, oils.
Peanut oil. This bland oil is made from pressed, steam-cooked peanuts. It has a fairly high smoke point and is good for cooking methods that involve high heat, such as frying, because it does not absorb or transfer flavors.
Pumpkin seed oil. This oil is made by pressing roasted, skinless pumpkin seeds and has an intense, nutty taste.
Rice bran oil. This mild oil is extracted from the germ and inner husk of rice. Rice bran oil is popular in Asian cuisine because of its high smoke point and suitability for high-temperature cooking methods such as deep-frying and stir-frying.
Sesame oil. This pressed oil is made from either untoasted sesame seeds, resulting in a light-colored oil, or toasted sesame seeds, for a dark-colored oil. Light sesame oil has a nutty flavor and is good for frying, while dark sesame oil has a strong flavor and is generally added to dishes in small quantities for flavor just before serving. Sesame oil has a high smoke point and is the least prone among oils to turn rancid. It is a good source of both monounsaturated fat and polyunsaturated fat.
These oils are high in polyunsaturated fat, which is also considered a heart-healthy fat.
Corn oil. This tasteless oil is made from the germ of the corn kernel and is widely used in cooking because it is inexpensive and has a high smoke point. Corn oil is a common ingredient in margarine.
Cottonseed oil. This oil is extracted from the seeds of the cotton plant after the cotton lint has been removed. It is commonly used to make snack foods such as potato chips.
Flaxseed oil. This oil is made from the seeds of the flax plant and is often used as a dietary supplement rather than a cooking oil. It is high in omega-3 fatty acids and contains a group of chemicals called lignans that may play a role in cancer prevention.
Grapeseed oil. This light-tasting, medium-yellow oil is pressed from seeds of various varieties of grapes and is a by-product of wine making. It has a high smoke point and is typically used in salad dressings and marinades and for stir-frying.
Safflower oil. This oil made from the seeds of the safflower plant is almost flavorless and colorless. It is a favorite for salad dressing, because it does not solidify when chilled, and is also used in cooking. Safflower oil that is labeled “high-oleic” has a higher monounsaturated fat content than safflower oil that is not so labeled.
Soybean oil. This refined, mild oil is produced by cracking soybeans and chemically extracting the oil. Soybean oil is high in omega-3 fatty acids and is used extensively in commercially prepared foods but less often as a home cooking oil.
Sunflower oil. This light, odorless oil is pressed from sunflower seeds and is a good all-purpose oil. Like safflower oil, sunflower oil labeled “high-oleic” is higher in monounsaturated fat than sunflower oil not labeled with that term.
Walnut oil. This oil is extracted from walnuts and has a delicate, nutty flavor. It is high in omega-3 fatty acids but is not used for high-temperature cooking because heating it can diminish the flavor and produce a slight bitterness.
A high intake of oils high in saturated fat can lead to a high LDL cholesterol level.
Coconut oil. This oil, also known as coconut butter, is extracted from the inner flesh of coconuts. It has a longer shelf life than other vegetable oils and is highest in saturated fat of all cooking oils. Unrefined, or virgin, coconut oil is derived from fresh coconut. Refined coconut oil is derived from copra, the dried coconut meat.
Palm oil. Palm oil is obtained from the fruit of the palm tree. It is reddish in color because it contains high amounts of beta-carotene. It is also high in saturated fat and semisolid at room temperature. Palm oil is the most widely produced vegetable oil in the world and is used primarily in processed foods.
Palm kernel oil. Palm kernel oil is extracted from the seeds, or kernels, of the palm fruit. It is also high in saturated fat and is most widely used in processed foods.
All cooking oils, whether refined or unrefined, are sensitive to light, heat, and exposure to oxygen (air). Cooking oil that is spoiled (rancid) will have an unpleasant smell and taste. To prevent spoilage, store oils in the refrigerator or in a cool, dark place. Oils may thicken in the refrigerator, but they will return to liquid if left standing at room temperature. Refined oils that are high in monounsaturated fats will keep for up to a year. Cooking oils high in polyunsaturated fats such as soybean, corn, safflower, and canola spoil more quickly: If stored properly, these oils will keep for up to six months. Some manufacturers put “use by” dates on product labels.
Remember that all cooking oils contain the same number of calories — about 120 calories per tablespoon — and contain no trans fat or cholesterol. Because cooking oils are 100% fat and are high in calories, use as little as possible. To minimize the amount of oil you use when cooking on the stovetop, try using nonstick pans and an oil mister to spray a thin coating of oil onto the pan. When you need more than a thin coating of oil, use measuring spoons or cups to carefully measure out the desired amount.
For heart health, select cooking oils with the lowest levels of saturated fat and the highest levels of monounsaturated and omega-3 fatty acids. Examples of heart-healthier oils include canola oil, olive oil, flaxseed oil, and walnut oil. If you are looking for an oil to add flavor to your cooked dishes or salad dressing, choose a nut oil, toasted sesame oil, or an unrefined olive oil. And for more information on various cooking oils, see “Check Your Oil.”
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