Balancing omega-3 and omega-6 fatty acids.
Recommended amounts of fats have changed as scientists gain a better understanding of the different types of fatty acids. To meet the current total fat recommendation of 20 to 35 percent of calories, the 2005 United States Dietary Guidelines for Americans advise that most dietary fats should come from sources of polyunsaturated and monounsaturated fatty acids. The Institute of Medicine's Dietary Reference Intakes (DRI's) identify recommended daily amounts of omegas-6 and omega-3 fatty acids. The American Heart Association (A.H.A.) bases its recommendations of omega-3 fatty acids on risk for coronary heart disease and provides guidelines for intakes of foods with omega-6's.
Ongoing studies have led to the premise that a balance of omega-6 and omega-3 fatty acids is necessary to maximize the benefits of these fats. According to some scientists, diets higher in omega-6 relative to omega-3 appeared to be associated with an increased prevalence of heart disease, cancer, and autoimmune disease. This new knowledge led to a proposed "intake ratio" of omega-6 to omega-3 fatty acids.
The ratio of omega-6 to omega-3 fatty acids our diet today is estimated to be more than 10:1; some estimates are as high as 30:1. A few studies suggest that a lower ratio of omega-6 to omega-3 (between 2:1 and 5:1) would be better for reducing the risk of disease. Yet some nutrition scientists question the validity of a target ratio; they claim that using a ratio as dietary advice is difficult to measure and implement. In addition, there are flaws in applying a target ratio for assessing risk.
Benefits of Omega-3 and Omega-6 Fats
Unsaturated fatty acids are classified as omega-3 or omega-6 based on their chemical structure. Both classes comprise several fatty acids, including two essential fatty acids that must be supplied by the diet. These essential fatty acids are critical for normal growth and functioning of the cells, muscles, nerves, and organs.
Omega-3 fatty acids include the essential alpha-linolenic acid (ALA), which is provided in the diet mainly through plants, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA is found mainly in flax, flaxseed oil, canola oil, walnut oil, and dark green leafy vegetables. Nuts are also a good source of omega-3 fatty acids (hazelnuts, almonds, pecans, cashews, walnuts, and macadamia nuts).
Omega-3 fatty acids generally decrease serum triglyceride and total cholesterol levels, but they may increase or may have no effect on high-density-lipoprotein (HDL) cholesterol. Besides lowering the risk of heart disease and stroke, omega-3 fatty acids may help reduce blood pressure, depression, joint pain, and other rheumatoid problems. Potential benefits may include reducing symptoms of attention deficit hyperactivity disorder (ADHD), boosting the immune system, and possibly protecting against Alzheimer's disease. Omega-3's may also aid in neurological development in young children.
Omega-6 fatty acids include the essential linoleic acid (LA), found mainly in corn oil, soybean oil, and some seeds. LA is converted in the body to arachidonic acid (AA). Diets high in omega-6 fatty acids are associated with lower levels of total cholesterol and low-density lipoprotein (LDL) cholesterol but also with lower levels of protective HDL cholesterol.
Sorting Out the Facts: Are Omega 6's Unhealthful?
Establishing a target ratio for intake of omega-6/omega-3 fatty acids may actually be based more on myth than fact.
Myth: We are not consuming omega-6 fatty acids in accordance with dietary recommendations.
Fact: Scientists believe that humans evolved on a diet that provided about equal amounts of omega-6 and omega-3 fats. Over time, it became possible to mass-produce vegetable oils, and the use of these omega-6 rich oils has become more prevalent in the food supply. According to the National Health and Nutrition Examination Survey (NHANES) 2001-2002, average daily intakes of both omega-6 and omega-3 fatty acids were close to recommendations suggested by the Institute of Medicine.
Furthermore, since both omega-6 and omega-3 fatty acids are essential in the diet, it may be preferable to use the absolute amounts of both fats rather than a ratio of the two when determining intake.
Myth: Omega-6 fatty acids interfere with the health benefits of omega-3's.
Fact: This belief is based on experimental evidence suggesting that omega-6 fatty acids compete with omega-3 fatty acids for common enzymes needed for metabolism, possibly counteracting the health benefits of the omega-3's. Omega-3 fatty acid metabolism produces eicosanoids that inhibit inflammation, blood clotting, and arrhythmias and decrease blood pressure. In contrast, omega-6 metabolism produces eicosanoids that are released in response to injury, infection, or disease, and they can promote inflammation, blood clotting, and hypertension.
Myth: A greater omega-6 to omega-3 ratio indicates a higher risk of heart disease.
Fact: A high ratio might be the result of a relatively high intake of omega-6 fatty acids, a low intake of omega-3 fatty acids, or both. Actually, higher intakes of both omega-6 and omega-3 fatty acids are associated with cardiovascular risk reduction. There is no evidence that lowering omega-6 fatty acid intake results in a reduced risk of heart disease. However, increasing the omega-3s does reduce the ratio and the risk, regardless of the amount of omega-6 in the diet. When researchers compared the effects of omega-6 with omega-3 following a low-saturated-fat diet, both types of fatty acids improved blood lipid levels. Other studies indicate that omega-6 is protective, not harmful, and they even suggest that omega-6 and omega-3 may have synergistic effects by working together to reduce heart disease risks. The A.H.A. advises that omega-6 fatty acids might be a good fat that promotes a reduced risk of heart disease.
A diet with a moderate fat intake (20 to 35 percent of calories), consisting of mostly good fats (polyunsaturated and monounsaturated fatty acids), supplies important essential fatty acids and may protect against heart disease. Trying to achieve a ratio of omega-6 to omega-3 fatty acids may distract from the more important matter of including more beneficial fats in the diet. It would be prudent to obtain more omega-3 fatty acids and to replace trans and saturated fatty acids with polyunsaturated and monounsaturated fatty acids when possible. Including foods rich in omega-3s and omega-6s, such as seeds, nuts, flaxseed, and vegetable oils (canola, soybean, safflower, sunflower, and corn), is a simple strategy that might improve overall health.
(Source: Adapted from Food Insight, March/April 2008.)
RELATED ARTICLE: Eye problems and omega-3.
The risk of age-related macular degeneration (AMD) may be reduced by a diet rich in olive oil and omega-3 fatty acids and low in trans-unsaturated fat.
(Source: Archives of Ophthalmology, 2009; 127:674-680.)
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|Publication:||Nutrition Health Review|
|Date:||Mar 22, 2010|
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