Health Effects of Dietary Fatty Acids
Contrary to common belief, consumption of fat is not unhealthy. Fat is not the main villain in the American diet. The villain is the types of fats in our diets. The snacks, fried foods and processed foods, all high in omega-6 oils and trans fats, have become dominant in American diets. Large amounts of these fats can alter the body’s metabolism. It becomes easier for cells to store rather than burn. The result is weight gain. Large amounts of these fats can also accelerate aging and increase risk for heart diseases and inflammatory diseases.
But in truth, human beings must have a moderate amount of the right fats in the diet for proper growth and optimal health. Dietary fat is needed to carry fat-soluble vitamins A, D, E and K from our food into the body. Blood serum circulates fat as triglycerides in the bloodstream throughout the body. The fat serves as fuel for energy and is a major constituent in all cell membranes. The individual fatty acids which make up the fats carry out the different functions in the body. Since each fatty acid can exert remarkably different effects on human health, an understanding of the right kinds and amounts of fats in the diet is crucial for optimal health.
Saturated fats are associated with increased risk of heart disease and other health risks. However, some saturated fatty acids are needed to give stiffness and integrity to cell membranes while unsaturated essential fatty acids are needed for flexibility. Saturated fats are a major energy source. But, too much saturated fat raises total blood cholesterol as well as low density lipoprotein (LDL) cholesterol. In reality, saturated fats raise total blood cholesterol levels more than dietary cholesterol because they tend to boost both good high density lipoprotein (HDL) and bad LDL cholesterol. These negative effects point to the importance of limiting the amount of saturated fats in the diet.
The human body burns both saturated and monounsaturated fats as fuels. But unlike saturated fats, studies show that monounsaturated fatty oils lower LDL cholesterol and may also lower blood pressure. Monounsaturated oils are not as easily oxidized as the more unsaturated oils thus they do they do not become rancid as quickly. Olive oil, the best known source of monounsaturated oils containing 71 percent oleic acid, can also decrease the risk of blood clots because it contains squalene, a compound with anti-clotting properties. Olive oil is a healthy choice for the diet, but it cannot be the sole fat in a healthy diet since it does not contain the essential fatty acids needed for many crucial body functions.
Even as late as the 1990s, there was little distinction of known health benefits between the two families of polyunsaturated oils (omega-3 and omega-6). Both were low in saturated fat and cholesterol leading to recommendations to use polyunsaturated oils rather than animal fats in food preparation. Since the most readily available polyunsaturated oils are the omega-6 vegetable oils, this recommendation has led to a very high consumption of omega-6 oils, During the past decades the numbers of fast food chains have mushroomed, with their menus filled with tempting foods fried in vegetable oils. Food processors have expanded their lines of snack foods and other processed foods that are made with hydrogenated vegetable oils. Dramatically increased consumption of these foods has given rise to the American diet that is overloaded in omega-6 fatty acids. At the same time, data show that few Americans consume relatively small amounts of omega-3 fatty acids found in marine fish.
Essential Fatty Acids
The human body can make most of the fatty acids needed for good health, including saturated and unsaturated fatty acids. But there are certain polyunsaturated fatty acids that cannot be made, so they must be included in the diet. They are called essential fatty acids and include members of both the omega-3 and the omega-6 families. Both families are precursors for the formation of eicosanoids, potent hormone-like compounds that regulate cell growth, inflammation, blood clotting and many aspects of the immune function. The three major eicosanoid families include prostaglandins, thromboxanes and leukotrienes. Eicosanoids derived from the omega-6 family act in an opposite manner from those derived from the omega-3 family even though their structures are very similar. Eicosanoids, unlike hormones made in particular glands and stored until needed, are, instead, synthesized for immediate use in all cells of the body except red blood cells.
Both omega-3 and omega-6 derived eicosanoids must be in a proper balance for the body to stay healthy. A diet high in omega-6 fatty acids and low in omega-3 fatty acids will signal the body to produce hormones that lead to chronic inflammation. Chronic inflammation leads to higher risk for inflammatory and autoimmune diseases, blood clots and certain cancers.
Inflammation is the immune system’s response to an injury or an intruder such as a virus, an allergen or a foreign chemical. The immune system reacts by releasing white blood cells and hormones into the bloodstream causing inflammatory responses such as swelling, redness and pain. Chronic inflammation can strike eyes, face, brain, kidneys, stomach, pancreas, throat, intestines, gums, lungs, skin, tendons, blood vessels and other areas of the body. When inflammation is not turned off, it can lead to inflammatory diseases such as psoriasis, lupus, acne, conjunctivitis, Alzheimer’s, Crohn’s disease, atherosclerosis, heart disease, diabetes, colitis, gingivitis and various cancers. A diet high in omega-6 fatty acids increases the risk of developing one or more of these inflammatory diseases. A diet high in omega-3 fatty acids decreases these risks.
Research has shown that a diet high in omega-3 fatty acids reduces the risks of cardiovascular diseases by decreasing growth of atheroschlerotic plaque, decreasing risk of blood clots, decreasing arrhythmia, decreasing triglyceride levels, lowering blood pressure and improving arterial health.
Omega-3 Essential Fatty Acids
The omega-3 family of fatty acids comes from the essential fatty acid, alpha-linolenic acid, sometimes referred to as the plant or short-chain omega-3 fatty acid. The body can convert alpha linolenic fatty acid to the very long chain omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), but the process is inefficient (less than 1% to 5%). Therefore, EPA and DHA are also considered essential fatty acids, especially during pregnancy and early childhood in the development of the brain, visual and vascular functions. EPA and DHA, when taken in therapeutic amounts of three to four grams per day, can lower blood triglycerides and raise HDL cholesterol. Land plants do not contain EPA or DHA. We must obtain them by including fish from marine waters in the diet.
Omega-6 Essential Fatty Acids
The omega-6 family comes from the essential fatty acid linoleic acid found primarily in oils of grain seeds. These oils are plentiful in the American diet. The body can convert linoleic to arachidonic acid (AA) but AA is referred to as an essential fatty acid since it is critical in early childhood development. See Naming fatty acids.
Trans fats are produced when vegetable oils are commercially hydrogenated to produce a hardened, pliable fat product. When vegetable oils are partially hydrogenated, some of the oil remains unsaturated, but the hydrogen atoms at the double bonds are rearranged such that the molecule is straightened and resembles a saturated fat. This process results in a product that has better physical properties for use in cooking but can contain fairly high concentrations of trans fatty acids. Trans fats are problematic for human consumption since they closely resemble natural food fats and are readily incorporated into cell membranes. Once they are incorporated into the cell membranes, their altered chemical structure interferes with normal metabolism. Studies have shown that trans fats behave similarly to saturated fats in that they raise bad LDL cholesterol. But even worse, trans fats also lower the good HDL cholesterol. Trans fats accelerate inflammation, an over-activity of the immune system that has been implicated in heart disease, stroke, diabetes, and other chronic conditions.
The United States Food and Drug Administration (FDA) now require that all food labels state the number of grams of trans fat in one serving of that food product. While limiting intake of saturated fats is important, trans fats should be eliminated from the diet. Food processors who have removed trans fats from their products or have produced new products without trans fats proclaim zero trans fats on their label. Some fast-food chains are also eliminating trans fats from their products. New York City is the nation’s first city to ban trans fats. Their city’s Board of Health voted unanimously to force eateries to remove trans fats from most frying oils by July 2007 and from all foods by July 2008.