There are myriad culinary uses for fats and oils including cooking, tenderizing baked goods and adding richness, texture and flavor to foods. Fat is one of the body's basic nutrients, providing energy by furnishing calories. All forms of fat are made up of a combination of fatty acids, which are the building blocks of fats much as amino acids are the building blocks of proteins. Fats and oils are either saturated or unsaturated, the latter classification being broken down into monounsaturated and polyunsaturated fats. To illustrate the difference between the terms saturated, monounsaturated and polyunsaturated, picture a fat molecule as a train of passenger cars (carbon atoms). If every seat on the train is filled by a "passenger" (hydrogen atom), then this is a saturated fat molecule. If there's one seat open in each car where a hydrogen-atom "passenger" can sit, the molecule is monounsaturated; if there are several seats available, it's polyunsaturated. In general, saturated fats come from animal sources and are solid enough to hold their shape at room temperature (about 70°F). Exceptions to this rule are tropical oils such as coconut oil and palm oil, which, though of plant origin, are semisolid at room temperature and highly saturated. Saturated fats are the nutritional "bad guys" because they're known to be associated with some forms of cancer and to increase cholesterol levels, which can be a contributing factor to heart disease. In addition to the two aforementioned tropical oils, the most commonly commercially used saturated fats are butter, lard, suet and hydrogenated vegetable oils such as margarine and vegetable shortening. Hydrogenated (or partially hydrogenated) oils have been chemically transformed from their normal liquid state (at room temperature) into solids. During the hydrogenation procedure extra hydrogen atoms are pumped into unsaturated fat. This process creates trans fatty acids, converting the mixture into a saturated fat and obliterating any benefits it had as a polyunsaturate. Some researchers believe that hydrogenated oils may actually be more damaging than regular saturated fats for those limiting cholesterol in their diets. Unsaturated fats are derived primarily from plants and are liquid (in the form of an oil) at room temperature. Generally speaking, oils are composed (in varying percentages) of both monounsaturated and polyunsaturated fats. Monounsaturated fats are known to help reduce the levels of ldl (the bad) cholesterol. The three most widely used oils that are high in monounsaturates are olive oil, canola oil and peanut oil. Polyunsaturated fats are also considered relatively healthy and include the following, ranked in order, most to least, of polyunsaturates: safflower oil, soybean oil, corn oil and sesame oil. Omega-3 oils are a particular classification of fatty acids found in some plants (such as flax seed) and in the tissues of all sea creatures. These special polyunsaturated oils have been found to be particularly beneficial to coronary health (purportedly lowering the bad ldl cholesterol and elevating the good hdl) as well as to brain growth and development. Among the popular fish that are particularly good sources of Omega-3 oil (in order of importance) are sardines, herring, mackerel, bluefish, tuna, salmon, pilchard, butterfish and pompano. High cooking temperatures can destroy almost half the Omega-3 in fish, whereas microwave cooking doesn't appear to have an adverse effect on it. Canned tuna packed in water is a quick and easy way for many people to get their Omega-3 oil, but it's worth noting that combining it with the fat in mayonnaise offsets any positive effects. Canned salmon and sardines are also excellent Omega-3 sources. Storing fats and oils. Saturated fats such as butter, margarine and lard should be tightly wrapped and refrigerated. They can usually be stored this way for up to 2 weeks. Hydrogenated vegetable shortening can be stored, tightly covered, at room temperature for up to 3 months. Refined oils, sealed airtight, can be stored on the kitchen shelf up to 2 months. Oils with a high proportion of monounsatu-rates — such as olive oil and peanut oil — are more perishable and should be refrigerated if kept longer than a month. See also almond oil; animal fat; chili oil; cocoa butter; cottonseed oil; fat substitutes; grapeseed oil; grease; hazelnut oil; milk fat; oils; pumpkin seed oil; sunflower seed oil; trans fatty acids; walnut oil.