Although much attention has been focused on the need to reduce the amount of fat in the diet, the body does need some fat. During infancy and childhood, fat is necessary for normal brain development. Throughout life, it provides energy and supports growth. Fat is, in fact, the most concentrated source of energy available to the body. However, after the age of two, the body requires only small amounts of fat—much less than what is provided by the average American diet.
Fats are composed of building blocks called fatty acids. There are three major categories of fatty acids—saturated, polyunsaturated, and monounsaturated. Saturated fatty acids are found primarily in animal products, including dairy items such as whole milk, cream, and cheese, and fatty meats such as beef, veal, lamb, pork, and ham. The fat marbling that you see in beef and pork is composed of saturated fat. Some vegetable products—including coconut oil, palm kernel, oil, and vegetable shortening—are also high in saturates. The liver uses saturated fats to manufacture cholesterol. Therefore, excessive dietary intake of saturated fats can significantly raise the blood-cholesterol level, especially the level of low-density lipoproteins (LDLs), or “bad” cholesterol.
Let's take short break here and talk about this "bad" cholesterol. We typically think that just by eating foods that have any fats in them that we'll just accumulate these bad particles of fat and they'll just start depositing in our blood vessels. What most people don't realize is that our body makes most of our cholesterol (about 75%), whereas only 25% is taken in with food. The two different types of "lipoproteins" (high and low density) have opposite purposes: the low-density bring fats to the cells from the liver, the high brings it back to the liver from the cells. Thus, we tend to think that too much LDL brings too much fat to the cells. However, in ALL of the scientific literature on the studies done on LDL, they evaluate "oxidized" LDL, which means that the LDL has been acted upon by oxygen. When this happens, the LDL develops "whiskers" or sharp edges to them. These sharpened particles are flowing around our blood stream and will create small "cuts" inside the blood vessel. The body senses this and sends the inflammatory signal to heal these small wounds. This is what starts the process of accumulation of materials inside the blood vessel, that eventually turns into plaque. If there are enough "antioxidants" in our system (to prevent the oxidation process), then the LDL will not oxidize and will complete their mission successfully.
Polyunsaturated fatty acids are found in the greatest abundance in corn, soybean, safflower, and sunflower oils. Certain fish oils are also high in the polyunsaturates. Unlike the saturated fats, the polyunsaturates may actually lower your total blood-cholesterol level. In doing so, however, they also have a tendency, when present in large amounts, to reduce your high-density lipoproteins (HDLs), or “good” cholesterol. For this reason, the guidelines state that the intake of polyunsaturated fats should not exceed 10 percent of the total caloric intake.
Monounsaturated fatty acids are found mostly in vegetable and nut oils such as olive, peanut, and canola. These fats appear to reduce the LDL blood level without affecting the HDL level in any way. However, this positive impact upon LDL cholesterol is relatively modest. The guidelines recommend that the intake of monounsaturated fats be kept between 10 and 15 percent of the total caloric intake.
Although most foods contain a combination of all three types of fatty acids, one of the types is usually predominant. Thus, a fat or oil is considered saturated or high in saturates when it is composed primarily of saturated fatty acids. Saturated fats are usually solid at room temperature. A fat or oil composed mostly of polyunsaturated fatty acids is called polyunsaturated, while a fat or oil composed mostly of monounsaturated fatty acids is called monounsaturated.
We have recently begun to increase our awareness of trans fats. Basically, trans fat is produced when manufacturers add hydrogen to vegetable oil--a process called hydrogenation. Hydrogenation increases the shelf life and flavor stability of foods containing these fats. Partial hydrogenation is a similar process where the action of hydrogenation is halted partially through the process so that all of the fat is not converted.
Trans fat can be found in vegetable shortenings, some margarines, crackers, cookies, snack foods, and other foods made with or fried in partially hydrogenated oils. Unlike other fats, the majority of trans fat is formed when food manufacturers turn liquid oils into solid fats like shortening and hard margarine. A small amount of trans fat is found naturally, primarily in dairy products, some meat, and other animal-based foods.
Trans fat, like saturated fat and dietary cholesterol, raises the LDL cholesterol that increases your risk for coronary heart disease. Americans consume on average 4 to 5 times as much saturated fat as trans fat in their diets. Although saturated fat is the main dietary culprit that raises oxidized LDL, trans fat and excessive dietary cholesterol also contribute significantly.
There has been much information in the press about the Essential Fatty Acids (EFAs). However, much of it is misguided in regard to the effects on the eyes. The most widely discussed EFAs are the Omega-3 and the Omega-6 essential fatty acids. Omega-6 fatty acids are the most plentiful in our diet. They are in most everything we eat that contains fat, including meat, most seed oil, dairy products and eggs. Omega-3 fatty acids are available in many seed oils and most all cold-water fatty fish. A proper balance of these fatty acids is essential to good health. The daily intake recommendation of the Institute of Medicine is 4:1 - four times as many Omega-6 fatty acids as Omega-3 fatty acids. However, do not mistake ALL fats for trans fats; the hydrogenation process ruins ALL fats and makes them dangerous.
Fatty acids are stored in every cell membrane of our body. They have two primary functions. Firstly, they ensure cellular fluidity, acting as sentinel gatekeepers for every cell – allowing vital nutrients to enter the cell and forcing destructive free radical debris out of the cells. Secondly, both Omega-6 and Omega-3 fatty acids can be converted into three different types of active molecules called prostaglandins (PGEs). Without going into too much detail, prostaglandins achieve three processes: reduce inflammation and inhibit blood clotting (PGE1); constrict blood vessels, increase body temperature, and encourage blood clotting (PGE2); and plays an important anti-inflammatory role (PGE3). All three of these prostaglandins are important for the body to maintain its’ health and balance.
Two nutritional fatty acids are docosahexaenoic acid (DHA) and arachidonic acid (ARA). DHA, a long-chain omega-3 fatty acid, is found in tissues throughout the body. DHA is a major structural and functional element of all membranes in the gray matter of the brain and the retina of the eye. It is also a key component of heart tissue. DHA is important for optimal brain and eye development in infants and has been shown to support brain, eye and cardiovascular health in adults. ARA, a long-chain omega-6 fatty acid, is the principal omega-6 in the brain, and it is abundant in other cells throughout the body. ARA is equally important for proper brain development in infants and is a precursor to a group of hormone-like substances called eicosanoids. Eicosanoids are important in immunity, blood clotting and other vital functions in the body. Humans obtain ARA by eating foods such as meat, eggs and milk, whereas DHA is found in a limited selection of foods such as fatty fish and organ meats. The body can also synthesize DHA from its precursor alpha-linolenic acid (ALA) but this process is inefficient. Both fatty acids occur naturally in breast milk and support the mental and visual development of infants. The health benefits of DHA extend from prenatal development through adult life.
So what is a good dietary balance of the macronutrients? Most experts agree that a good diet consists of about 2000 calories a day. A proper balance consists of about 30% (600 calories) from fat–mostly monounsaturated oils and only 7% of which should be saturated fat, 50-60% carbohydrates (1000-1200 calories)–mostly low-glycaemic index complex carbohydrates and about 10-20% (200-400 calories) from protein. These amounts could certainly vary from one individual to another but are generally considered a good starting point for a healthy diet.