Most Americans eat too much fat -- and too many calories. That, along with a lack of exercise, has led to an epidemic of obesity and diabetes and contributed to keeping heart disease as the leading cause of death in the United States. But what about omega-3 fatty acids?
Omega-3s are a beneficial and essential form of fat, one that your body needs but can't make. Although your body needs two forms of omega fatty acids -- omega-3 and omega-6, it is the omega-3s that get high marks from researchers. They believe that omega-3s help prevent coronary heart disease (CHD) in healthy people and slow progress of the disease in those who already have it.
CHD is caused by atherosclerosis, a long-term process in which fatty deposits of plaque build up on the inside of the coronary arteries, the blood vessels that supply the heart muscle with oxygen and nutrients. Eventually, the coronary arteries become so narrow that the flow of blood to the heart muscle is decreased or easily blocked by plaque or a blood clot. CHD can produce chest pain, called angina; heart attack; or both.
Atherosclerosis begins when the inside wall of an artery is damaged by high levels of cholesterol and triglycerides, another form of fat in your blood, and by inflammation. A diet high in fat, particularly saturated fat, increases cholesterol and triglycerides. Artery damage can also be caused by high blood pressure, tobacco smoke or diabetes. To help prevent heart disease, you should keep your cholesterol and triglycerides at or below recommended levels. According to the National Heart Lung and Blood Institute, that means a total cholesterol level of less than 200 mg/dL and a triglyceride level of less than 150 mg/dL.
To lower your levels of cholesterol and triglycerides, you should maintain a healthy weight; do moderately strenuous physical activity most days of a week; eat a diet rich in vitamins, minerals and fiber; and include fish containing omega-3 fatty acids at least twice a week.
In the average American's diet, about 20 percent of calories that come from fat are omega-3 and omega-6 fatty acids; most of the omega fatty acids are omega-6s. Omega-6s may contribute to the development of atherosclerosis, but experts have found that people who eat foods with high levels of two of the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have low rates of CHD.
EPA and DHA are also called marine omega-3s because they are found in fatty fish such as mackerel, lake trout, herring, sardines, albacore tuna and salmon. They are also in supplements called fish oils. Another source for EPA and DHA is alpha-linolenic acid, which is found in soy and canola oils, flaxseed, walnuts and other nuts. It can be converted into omega-3 fatty acids in the body, but its benefit in preventing heart disease is not as clear.
Here's how experts believe omega-3 fatty acids may reduce the risk for CHD:
They decrease the risk for arrhythmia, an abnormal heart rhythm, which can lead to sudden cardiac death.
They decrease triglyceride levels, possibly by as much as 20 to 50 percent, depending on how much omega-3 you consume.
They decrease the growth rate of plaque that clogs blood vessels.
They lower blood pressure slightly, but this effect depends on how much omega-3 you consume.
They help prevent inflammation of the blood vessels and formation of blood clots.
The American Heart Association (AHA) recommends that healthy people who do not have heart disease eat some type of fatty fish at least twice a week and include oils and foods rich in alpha-linolenic acid in their diet. Flaxseed, canola and soybean oils, flaxseed and walnuts contain this acid. People with heart disease can take 1 gram of a supplement of EPA+DHA a day. People who need to lower triglycerides to decrease their risk for CHD can take 2 to 4 grams a day.
Food is the best way to get omega-3 fatty acids because food contains other healthy substances. For example, fish contains arginine, glutamine and selenium, all of which may benefit the heart and blood vessels. Flaxseed and walnuts have substances that help lower total cholesterol.
The AHA offers this rundown on the omega-3 content of some fish, per 3-ounce serving:
Canned light tuna: 0.26 to 0.73 grams
Shrimp: 0.27 grams
Fresh or frozen salmon: 0.68 to 1.83 grams
Cod: 0.13 to 0.24 grams
Catfish: 0.15 to 0.20 grams
Clams: 0.24 grams
Flounder or sole: 0.43 grams
Crabs: 0.34 to 0.4 grams
Scallops: 0.17 grams
Eating fish comes with a downside: There are some health risks. Some types of fish, especially the older, larger predatory fish, may contain high levels of toxins. Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers and coastal areas.
Methylmercury is found in shark, swordfish, king mackerel and tilefish, which is also called golden bass or golden snapper. This element is most dangerous in very young children and in women who are pregnant or likely to become pregnant. Fish low in mercury are shrimp, canned light tuna, salmon, pollock and catfish.
Polychlorinated biphenyls (PCBs), which may cause cancer, are found in freshwater fish living in polluted waters; these fish include lake trout, smelt and freshwater bluefish. PCBs also are found in some farmed fish such as salmon. Dioxin and similar compounds cause cancer, depress the immune system and affect the central nervous system. Farmed fish, especially salmon, have been found to be contaminated with dioxin levels three to 10 times higher than wild salmon.
The benefits and risks of eating fish vary, depending on a person's stage of life. These are the AHA's recommendations:
Children, pregnant and nursing women should avoid potentially contaminated fish, including shark, swordfish, king mackerel and tilefish.
Middle-aged and older men, and women after menopause should follow guidelines from the U.S. Food and Drug Administration and Environmental Protection Agency on how much fish to safely eat. For this age group, the benefits of eating fish outweigh the risks.
You should eat a variety of fish to help decrease potentially adverse effects from environmental pollutants.
Fish oil supplements may be a safer and easier way to reach the higher doses of omega-3s recommended for some people. The processing of fish oils seems to lower PCBs and other contaminates.
People with very high triglyceride levels can take Omacor, a prescription drug of omega-3-acid ethyl esters that contains high concentrations of EPA and DHA. The drug can lower very high triglycerides by as much as 45 percent. Although it is more expensive to buy than fish oil supplements, the drug contains about three times the dose found in supplements: 465 mg of EPA and 375 mg of DHA.
Although fish are the best sources of omega-3s, the supply of fish is decreasing and prices are rising, putting the sources of omega-3s out of the reach of many people's budgets. Fish also may not be available in the future, no matter how much you are willing to pay. Industrial fishing has depleted some of the world's fish stocks by about 90 percent since 1950, and the trend seems to be continuing. Although fish farming is expanding, experts think we probably do not have a sustainable supply of omega-3 fats.
If omega-3 supplies decrease or if you choose not to take them, and you have high triglyceride levels or other risks for CHD, there are other, well-tested medications available. For example, the vitamin niacin, fibric acid derivative drugs such as gemfibrozil (Lopid) or fenofibrate (TriCor), and statins all lower triglycerides and have other beneficial effects.