Types of Dietary Fats and Oils
Fats and oils are the common names for triglycerides that are found in food, found circulating in our blood stream, and are stored in our body fat cells. Fats that are liquid at or below room temperature are called oils. Fats and oils are the storage form of fatty acids. This storage unit is made up of one molecule of glycerol and three attached fatty acids. Each attached fatty acid can be different. Fatty acids can differ in carbon chain length as well as degree of saturation. They can be saturated (holding all the hydrogen atoms possible) or unsaturated (missing pairs of hydrogen atoms resulting in double bonds). Saturated fatty acids contain only single bonds between carbon atoms; monounsaturated fatty acids contain one double bond, and polyunsaturated contain two or more double bonds within the carbon chain.
All fats and oils, whether they are of animal or plant origin, are some combination of saturated fatty acids, monounsaturated fatty acids, or polyunsaturated fatty acids and are classified by their predominant fatty acid category. For example, olive oil contains approximately 77 percent monounsaturated, 9 percent polyunsaturated and 9 percent saturated fatty acids, and being mostly monounsaturated, it is classified as a monounsaturated oil. Beef tallow and butter are classified as a saturated fat, being composed of triglycerides with mostly saturated fatty acids. Oils that are predominantly polyunsaturated may be further characterized as omega-6 or omega-3 oils. Peanut, safflower, sunflower seed, cottonseed and soybean oils are classified as omega-6 polyunsaturated oils. Fish oil, flaxseed oil, walnut oil and canola oil are classified as omega-3 polyunsaturated oils.
Saturated Dietary Fats and Oils
Saturated fats are triglycerides dominated by fatty acids containing all of the hydrogen atoms possible. All edible plants and animals contain varying amounts of both saturated and unsaturated fatty acids. Food sources that contain relatively high amounts of saturated fats include meats, butter, cream, cheeses and many processed foods that use these ingredients in their production. Tropical oils such as coconut and palm oils are also high in saturated fatty acids. Oils that are high in saturated fats are partially solid at room temperature.
Monounsaturated Dietary Fats and Oils
Monounsaturated oils are triglycerides dominated by fatty acids with one double bond. Palmitoleic acid and oleic acid are the most common monounsaturated fatty acids occurring in nature. Olive oil contains 71 percent oleic acid and is considered the best source of monounsaturated oils. Canola oil contains approximately 60 percent oleic acid as well as 10-15 percent alpha-linolenic acid, a polyunsaturated omega-3 fatty acid. Nuts and avocados are also high in monounsaturated fats. As the number of double bonds in a fatty acid increases, the fluidity increases. Monounsaturated oils are liquid at room temperature but may partially solidify in the refrigerator.
Polyunsaturated Dietary Oils
Polyunsaturated oils are triglycerides dominated by fatty acids with two or more double bonds. They are liquid at room temperature and are referred to as oils. There are two distinct families of polyunsaturated fatty acids, omega-3 fatty acids and omega-6 fatty acids. The basic structural difference between these two families is that the omega-3 fatty acids have their first double bond located three carbon atoms from the end of the carbon chain, whereas the omega-6 fatty acids have their first double bond six carbons from the end of the chain. However, these two families of fatty acids exert opposite functions in the body. Both are critical (essential fatty acids) for good health. Differences in these two oils are described in the Fats Handbook.
Omega-3 oils. The principal or parent fatty acid in the omega-3 family is alpha-linolenic acid which is found in plants. Oils with high contents of alpha-linolenic acid include canola oil, flaxseed oil and walnut oil. Walnuts, flaxseed and dark green, leafy vegetables such as spinach are excellent sources of alpha-linolenic acid. Marine fish oil contains the longer chain omega-3 fatty acids and is the most unsaturated of all the oils. It is dominated by eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). See Fats Handbook. Oils with these highly unsaturated fatty acids are found only in seafoods and marine algae. Results of our research show that all warmwater fish contain these long chain omega-3 fatty acids.
Omega-6 oils. Linoleic acid is the principal or parent fatty acid in the omega-6 family and is the dominant fatty acid in the vegetable oils corn, soybean, sesame, safflower, sunflower and cottonseed. It is plentiful in nature and in our diets. The composition of vegetable oils depends on what plant seeds are used. Corn oil contains 58 percent linoleic acid while some varieties of safflower oil contain up to 78 percent linoleic acid. Soybean oil contains up to 68 percent linoleic acid and cottonseed oil, 54 percent. Processed foods such as cakes, crackers, pies and all deep-fried foods contain high concentrations of omega-6 oils. The omega-6 oils give processed food the textures and tastes that Americans enjoy.
Triglycerides in vegetable oils that have been commercially hydrogenated contain trans fats. These transformed fats are unnatural forms of unsaturated fatty acids. The hydrogenation process makes the unsaturated molecules that are "kinked" due to double bonds straighter so that the molecules pack tightly together producing a hardened, higher melting fat used for margarines, shortening, and partially hydrogenated spreads. This straightened molecule is referred to as a trans fat. Food products such as baked goods, doughnuts, chips and crackers and snack items made with these hydrogenated oils, plus all foods made with shortening contain trans fats. Trans fats are also produced in vegetable oils used in for deep-fat frying and other processes that routinely heated vegetable oils to high temperatures. Trans fats pose serious health consequences.