Striking a Balance: Omega-6 and Omega-3 Fatty Acids

Although some consumers still view fats as something to avoid, the awareness that certain fats can have beneficial effects on health is starting to resound. Of the types of fats in food, saturated and trans fats are considered major contributors to heart disease, while polyunsaturated and monounsaturated fats play important roles in promoting heart health. Within the family of polyunsaturated fats, omega-6 and omega-3 fatty acids have earned a reputation as "good" fats. When consumed in moderation to replace saturated and trans fatty acids, omega-6 and omega-3 fatty acids are well recognized as fats that can help reduce both blood cholesterol levels and risk for heart disease.

Recommended amounts of fats have evolved as scientists continue to gain better understanding of the diverse roles and effects of the different types of fatty acids. To meet the current total fat recommendation of 20 to 35 percent of calories, the 2005 US Dietary Guidelines for Americans advise that most dietary fats should come from sources of polyunsaturated and monounsaturated fatty acids. The Institute of Medicine’s (IOM) Dietary Reference Intakes (DRIs) identify recommended daily amounts of omega-6 and omega-3 fatty acids (see table). The American Heart Association (AHA) bases their intake recommendations for omega-3 fatty acids on risk for coronary heart disease along with providing general guidelines for consuming foods with omega-6 fatty acids.

Scientists continue to delve deeper into the health effects of the different types of fatty acids. Ongoing study of optimal amounts of polyunsaturated fats in the diet has led to the premise that a balance of omega-6 and omega-3 fatty acids is necessary for maximizing the benefits of these fats. Some scientists believe that diets high in omega-6 fatty acids relative to omega-3 fatty acids may be associated with the increased prevalence of chronic diseases, including heart disease and certain cancers. This has led to the proposed use of a target intake ratio of omega-6/omega-3 fatty acids for assessing health risk and making dietary recommendations.

The ratio of omega-6/omega-3 fatty acids in today’s diet is estimated to be more than 10:1, with some estimates as high as 30:1. A few studies suggest that a much lower ratio of omega-6 to omega-3 fatty acids, ranging between 2:1 and 5:1, is desirable in reducing the risk of disease, including heart disease, cancer, and autoimmune disorders. Yet, some nutrition scientists question the validity of a target ratio, arguing that use of a ratio as dietary advice for individuals is not only difficult to measure and implement, but there are flaws and limitations in applying a target ratio for assessing risk of disease. This article examines the ratio debate and presents the current consensus on omega-3 and omega-6 fatty acids.

Health Effects of Omega-6 and Omega-3 Fats
Unsaturated fatty acids can be classified as omega-6 or omega-3 based on their chemical structure. Both classes comprise a collection of several fatty acids, including two essential fatty acids that must be supplied by the diet because the body cannot produce them. These essential fatty acids are critical for normal growth and functioning of the cells, muscles, nerves, and organs.

The omega-3 fatty acids include the essential alpha-linolenic acid (ALA), which is primarily provided in the diet through plants, as well as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are primarily provided from seafood. ALA is found mainly in flax, flaxseed oil, canola oil, walnuts, and dark green leafy vegetables. The body has the ability to convert ALA into EPA and DHA, however the efficiency of this conversion is low. Food sources of DHA and EPA include fatty fish, such as salmon, trout, sardines, mackerel, and cod.

In general, omega-3 fatty acids decrease serum triglyceride and total cholesterol levels, and may increase or have no effect on high-density-lipoprotein (HDL) cholesterol. In addition to lowering the risk of heart disease and stroke, omega-3 fatty acids may help reduce symptoms of hypertension, depression, joint pain and other rheumatoid problems. Other potential benefits may include reducing symptoms of attention deficit hyperactivity disorder (ADHD), boosting the immune system, and offering protection from an array of illnesses, including Alzheimer’s disease. In young children, omega-3s also aid in neurological development.

The omega-6 fatty acids include the essential linoleic acid (LA) found mainly in corn and soybean oils, seeds and nuts. LA is converted in the body to arachidonic acid (AA), which also occurs naturally in meat, dairy, and eggs. Diets high in omega-6 fatty acids are associated with lower blood levels of total cholesterol and LDL-cholesterol, but also with lower blood levels of the protective HDL cholesterol.

Sorting Out the Facts
Establishing a target ratio for intake of omega-6/omega-3 fatty acids may actually contradict current knowledge and may be based more on myth than fact.

MYTH:  Americans don’t consume 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, agricultural and technological advances have made it 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, mean usual intakes of both omega-6 and omega-3 fatty acids are close to recommended intake levels suggested by the IOM in the DRIs (see table). 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 health benefits of omega-3 fatty acid consumption.

FACT:   This belief is based on experimental evidence that omega-6 fatty acids compete with omega-3 fatty acids for common enzymes needed for metabolism, possibly counteracting the health benefits of omega-3 fatty acids. The potential significance of this theory requires understanding of the effects of eicosanoids, hormone-like end products of the metabolism of omega-6 and omega-3 fatty acids. The metabolism of omega-3 fatty acids produces eicosanoids that inhibit inflammation, blood clotting, arrhythmias, and help to lower blood pressure. In contrast, the metabolism of omega-6 fatty acids produces eicosanoids released in response to injury, infection, or disease that promote inflammation and blood clotting and increase blood pressure.

Mozaffarian et al examined the interplay between omega-6 and omega-3 fatty acids and coronary heart disease risk in the Health Professionals Follow-up Study. During the 14-year study, food intake of over 45,000 men was recorded using a food frequency questionnaire at baseline and every four years. The results indicated that the men consuming 250 milligrams per day of omega-3 fatty acids from plant or fish sources had a 40 to 50 percent lower risk of sudden death, regardless of their omega-6 fatty acid intake and risk factors for heart disease. The findings from this research provide the strongest evidence to date that omega-6 fatty acids do not counteract the effects of either plant or fish sources of omega-3 fatty acids.

MYTH:  A high ratio of omega-6/omega-3 fatty acids indicates greater risk for heart disease.

FACT:   There are multiple ways in which a high (or low) ratio of omega-6/omega-3 fatty acids can occur. For instance, a high ratio may be the result of a relatively high intake of omega-6 fatty acids, a low intake of omega-3 fatty acids, or both scenarios. Ratios are typically used when higher levels of one factor and lower levels of the other factor are predictive of increased risk (e.g., the LDL/HDL lipoprotein ratio). Yet, higher intakes of both omega-6 and omega-3 fatty acids are associated with risk reduction.

There is no evidence that lowering omega-6 fatty acid intake, which will "improve" the ratio, will result in reduced risk for heart disease. However, increasing intake of omega-3 fatty acids lowers the ratio and reduces risk, regardless of the levels of omega-6 fatty acids in the diet. When researchers compared the effects of omega-6 fatty acids with omega-3 fatty acids in subjects following a low-saturated fat diet, both types of fatty acids were found to improve blood lipid levels. Other studies have confirmed that omega-6 fatty acids are protective, not harmful, and even suggest that omega-6 and omega-3 fatty acids may have synergistic effects in reducing risk for heart disease. The AHA advises that omega-6 fatty acids are one of the "good" fats that may help to reduce risk of heart disease.

Advice for Today
Evidence remains strong that a moderate fat diet (i.e., 20-35 percent of calories) consisting of mostly ‘good’ fats—polyunsaturated and monounsaturated fatty acids—supplies important essential fatty acids and offers protection against heart disease. Focusing on a ratio of omega-6/omega-3 fatty acids may distract from the more important issue of including more beneficial fats in the diet. An abundance of research supports the recommendation to obtain more omega-3 fatty acids and to replace sources of trans and saturated fatty acids with polyunsaturated and monounsaturated fatty acids, when possible. Including foods rich in omega-3 and omega-6 fatty acids, such as fish twice a week, seeds, nuts, flaxseed, and vegetable oils (canola, soybean, safflower, sunflower, and corn), are simple, health-promoting strategies to improve heart health.

Omega-6 and Omega-3 Fatty Acids: Recommended and Usual Intakes
 

Adequate Intake (AI), Men 19-50y 1

Usual Intake from Food, Men 19y+ 2 Adequate Intake (AI), Women 19-50y 1 Usual Intake from Food, Women 19y+ 2
Omega-3 (alpha-linolenic acid) 1.6 g/day 1.7 g/day 1.1 g/day 1.3 g/day
Omega-6 (linolenic acid) 17 g/day 16.8 g/day 12 g/day 12.7 g/day

1 Institute of Medicine, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids, 2002.
2 What We Eat in America, NHANES 2001-2002.

Dietary Advice for Omega-3 Fatty Acids
Healthy individuals (ages 2 and up) Eat a variety of (preferably fatty) fish at least twice a week (about 8 ounces total). Include oils and foods rich in alpha-linolenic acid (flaxseed, canola and soybean oils; flaxseed and walnuts).
Individuals with documented coronary heart disease (CHD) Consume about 1g of EPA+DHA per day, preferably from fatty fish. Consult a physician before supplementing.
Individuals with high triglyceride levels Consume 2 to 4g of EPA+DHA per day provided as capsules under a physician’s care.

Adapted from: “Fish and Omega-3 Fatty Acids,” American Heart Association; www.americanheart.org; accessed 5/15/07. Dietary Guidelines for Americans, U.S. Departments of Health and Human Services and Agriculture, 2005. www.healthierus.gov/dietaryguidelines; accessed 5/15/07.