Fat. The word has come to have a ring that is less than music to our ears but, in reality is a normal, and essential component in human nutrition. Technically, fat falls within a larger, more comprehensive group of compounds known as lipids, a class that also includes cholesterol, and a number of less familiar hormones and other substances.
      Fat is an important source of energy for the body, as are carbohydrates, but chemically is structured differently and is burned by the body at a much higher rate. Put another way, we need considerably less fat to burn a given number of calories than we do for carbohydrates, or protein for that matter. This also accounts for the reason idle individuals who consume a lot of fat that is not routinely burned off as energy generally have weight management problems.

      The fat molecule has a fundamental chemical structure known as glycerol, attached to which are individual component parts referred to as fatty acids. A combination of three fatty acids bound to glycerol defines the more complex compound we know as triglyceride.
      There are several important forms of fatty acids, each of which is also defined by its chemical structure. Simply put, fatty acids are primarily a combination of carbon and hydrogen atoms, with the number of hydrogens bound to the carbons in any particular molecule determining its structure, as well as how it is metabolized in the body.
      Saturated fatty acid. A molecule that contains the maximum number of hydrogen atoms bound to all of the carbon atoms, in other words, completely “saturated” with hydrogen.
      Monounsaturated fatty acid. Similar to the saturated form, with the exception that a single pair of hydrogen atoms are missing; or, put another way, “unsaturated” at a single location.
      Polyunsaturated fatty acid. A molecule that is missing two or more pairs of hydrogen atoms; or, unsaturated in many locations. This group is made up primarily of omega-3 and omega-6 fatty acids.
      Trans fatty acid. A polyunsaturated fatty acid in which some of the missing hydrogen atoms have been replaced by a manufacturing process known as hydrogenation (or partial hydrogenation). This results in a molecular structure in which the fatty acid solidifies at a higher temperature, allowing certain food products, such as vegetable shortenings and margarines to remain solid at room temperatures where before they would have liquefied.
      These names will probably be somewhat familiar sounding, primarily because of the amount of media attention given to fat and its relation to health, but that does not mean they are all bad. Like all other nutritional components, there are some forms of fat that are required by the body for normal function.

      No discussion about fat would be complete without cholesterol, though the latter is not fat, per se, but a close relative also in the lipid family of compounds. Please see our section on cholesterol for more information.

      Just about all food sources of fat contain the three natural forms of fatty acids, though some have much higher concentrations of one over the other. In the developed world, the primary source of fat in the average diet is animal fat, which is made up primarily of saturated fatty acids (or, more commonly referred to simply as saturated fat). Dairy products and certain plant oils, such as coconut and palm oil are also high in saturated fat. Monounsaturated fat is found most commonly in avocados, olive oil and peanut oil. Other vegetable oils, including safflower and sunflower oil, as well as fish oils, contain mostly polyunsaturated fat.

      Fat commonly gets a bad rap from the media and, perhaps more subtly, from food labeling itself. With “less fat” and “no fat” glaring at us from one ad to another, and from one product to another, you would think that we would all be better off avoiding it completely. This, of course, is not true.
      The human body can manufacture all of the saturated fat it requires on its own. This is not true, however, for certain polyunsaturated fats. There are a number of so-called, essential fatty acids, that can be derived from diet alone. The three most important, from a nutritional standpoint, are linoleic acid, arachidonic acid, and linolenic acid. Since the latter two can be synthesized from the former, linoleic acid becomes the key for essential dietary fat. The highest concentrations of this fatty acid are found in corn oil, safflower oil and soybean oil.

      The percent Daily Value (% DV) used on food labels in the U.S. is calculated using a Daily Reference Value (DRV) for adults of “less than 65 grams of fat” for a 2000 calorie diet, of which there should be “less than 20 grams of saturated fat.” Dietitians generally agree that no more than 30 percent of daily calories should be derived from fat, and no more than 10 percent of daily calories from saturated fat.
      Your specific requirement can be determined from the fat calculator below. This is an approximation, based upon 30 percent of total caloric intake per day as fat, and 10 percent of total caloric intake as saturated fat.

Enter total daily calories in the first box, and click "calculate."

calories      g of total fat/day    g saturated fat/day

      The essential fatty acids required by the body are involved in such functions as cell wall integrity, normal cholesterol metabolism, and the synthesis of essential, fat-related hormone-like compounds such as prostaglandins that operate as metabolic regulators.
      Most other consumed fat is burned off as energy or, if in excess stored by the body. When fat stores accumulate in excess, weight management becomes a problem, which of course leads to obesity. There is increasing evidence that links excess fat and obesity to a number of critical, health related issues. It is believed that the incidence of some forms of cancer are much higher in individuals with high fat diets, and of course heart disease has long been associated with obesity and high dietary fat intake. Some forms of high blood cholesterol are also related to high fat diets, and contribute to cardiovascular disease as well.
      Although the details may vary, the big picture is very clear: low fat diets are a major contributor to preventive health.