Research is showing that the oils contained in fish (as well as in some plant foods) — known as omega-3 fatty acids — may have several health benefits, especially for the heart. Here’s what the research says about omega-3 fatty acids and tips for how you can incorporate these healthful fats into your diet.
Understanding Omega-3 Fatty Acids
Omega-3 fatty acids are a particular type of polyunsaturated fatty acid, which, unlike artery-clogging saturated fats, are considered healthful. The term “omega-3” refers to their chemical structure.
Omega-3 fatty acids have anti-inflammatory properties and have been linked in the scientific literature with several health benefits, such as improving the symptoms of arthritis and preventing recurrence of glomerulonephritis (a type of kidney disease). Research is ongoing regarding benefits for mental health conditions, including mild depression, ADHD, and PMS. The strongest evidence to date has to do with omega-3's protective effects on the cardiovascular system.
The Benefits for the Heart
Two omega-3 fatty acids in particular, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are found predominantly in fatty fish such as salmon, mackerel, tuna, herring, and sardines, have been linked with improving cardiovascular health. They appear to make blood platelets less ‘sticky,’ thereby reducing the risk of blood clots that could lead to heart attack or stroke.
According to the American Heart Association (AHA), omega-3 fatty acids may have the following beneficial effects on the cardiovascular system:
- Decreased risk of cardiac arrhythmias (disturbances in the heart rhythm, which can lead to sudden cardiac death)
- Decreased risk of blood clot formation, which can lead to heart attack or stroke
- Decreased levels of blood triglycerides
- Decreased rate of plaque accumulation in the arteries
- Improved arterial elasticity and health
- Lowered blood pressure
Some Research Findings
A large US study of more than 84,000 women, published in the Journal of the American Medical Association, found that women who ate fish five or more times per week had a 34% lower risk of coronary heart disease compared with women who ate fish less than once a month. Women who ate fish two to four times per week experienced a similar benefit, with a 31% lower risk.
In an Australian study, researchers gave patients with high cholesterol either EPA and DHA supplements or placebo for 7 weeks, and found that those taking the supplements experienced significant improvement in the elasticity of their arteries (improved elasticity means less chance of blockages).
Non-Fish Sources of Omega-3s
Fish and fish oil supplements are not the only sources of omega-3 fatty acids. Some plant foods contain a type of omega-3 fatty acid called alpha-linolenic acid (ALA), which is converted to EPA and DHA in the body. The plant sources richest in ALA include the following:
- High concentration:
- Ground flaxseed
- Flaxseed oil
- Moderate concentration:
- Walnuts
- Soybean oil
- Tofu
- Canola oil
- Leafy greens
AHA Recommendations
Since 2000, the AHA has been recommending that healthy people eat at least two servings (3 ounces each) of fish per week. In 2002, they issued further recommendations for intake of omega-3 fatty acids for the following populations:
People without documented coronary heart disease should eat a variety of fish at least twice a week and include sources of ALA in the diet as well.
People with documented coronary heart disease should consume approximately 1 gram of EPA and DHA per day, preferably from fatty fish, or from supplements after consultation with a physician.
People who need to lower their triglycerides should consume 2 to 4 grams of EPA and DHA per day from supplements (because this amount is difficult to get just from eating fish), under the guidance of a physician.
The FDA recently approved one formulation of EPA/DHA for prescription in the USA: Omacor. The manufacturer expects the formulation to be available in pharmacies by October, 2005. Currently EPA/DHA from fish oil is available in numerous concentrations in pharmacies and health food stores.
A Few Words of Caution
Eating more fish and omega-3 fatty acids is a good idea for most people, but there are a few things to keep in mind:
- Greatly increasing your intake of fish oils could cause the harmless but annoying side effect of fishy-smelling belches. Recently, enteric coated preparations have been developed to decrease the ‘fishy aftertaste’ that some people experienced.
- A more serious side effect is the possibility of increased risk for bleeding, so consult your doctor before taking fish oil supplements, especially if you may be having surgery in the near future.
- If you take fish oil supplements, make sure the supplements have been stripped of excess vitamins A and D (fish oils are naturally rich in these vitamins), because large doses of fish oils could result in toxic levels of these vitamins.
- Some types of fish, including shark, swordfish, king mackerel, and tilefish, may be contaminated with mercury or other environmental pollutants. Therefore, pregnant and nursing women and young children are advised to avoid these types of fish. Seeking fish oil sourced from farm-raised fish decreases the mercury exposure risk, but increases the dioxin and PCP exposure risk. Omega-3 can now also be obtained by eating eggs from chickens which were fed DHA-laden feed.
Finally, it’s important to remember that the benefits of omega-3 fatty acids are likely to be less pronounced if they aren’t part of an overall diet that is healthful.
RESOURCES:
American Heart Association
http://www.americanheart.org
National Heart, Lung, and Blood Institute
http://www.nhlbi.nih.gov/
SOURCES:
Harper CR, Jacobson TA. The fats of life. Arch Int Med. 2001;161:2185–2192.
Hu FB, Bronner L, Willett WC, et al. Fish and omega-3 fatty acid intake and risk of coronary heart disease in women. JAMA. 2002;287:1815–1821.
Kris-Etherton PM, Harris WS, Appel LJ, et al. Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease [AHA Scientific Statement]. Circulation. 2002;106:2747-2757.
Nestel P, Shige H, Pomeroy S, et al. The n-3 fatty acids eicosapentanoic acid and docosahexanoic acid increase systemic arterial compliance in humans. Am J Clin Nutr. 2002;76:326–330.