The American Heart Association (AHA)recommends that people consume omega-3 fatty acids, found in the flesh of oily fish,for their heart-protective benefits. However,some types of fish contain high levels ofcontaminants, including mercury.
For most people, the benefits of eating fishoutweigh the risks. A study published in theJournal of the American Medical Association in 2002 found that omega-3s make blood lesslikely to form clots that cause heart attacks,and they also protect against potentially fatalirregular heartbeats. In addition, omega-3s raise levels of HDL (“good”) cholesterolslightly and can significantly help lowertriglycerides, which is good news especiallyfor people with diabetes, who have anincreased risk of heart disease. The goals forhealthy fasting blood triglyceride levels areless than 150mg/dl.
How Often Should You Eat Fish?
The AHA recommends that most people eatat least two 3-ounce servings of a varietyof seafood per week. Although there arevegetarian sources of omega-3 fats found incanola oil, walnuts, ground flax seeds and flaxseed oils, only fish contains the preformedessential fats, eicosapentaenoic acid (EPA)and docosahexaenoic (DHA) acid. Fatty fishsuch as salmon, trout, herring, mackerel,sardines, halibut and tuna have higher levelsof EPA and DHA, although the amount variesdepending upon the livelihood of the fish.
In September l994, the U.S. Food and DrugAdministration (FDA) approved the followingclaim that appears on the labels of foodscontaining omega-3 fatty acids:
Supportive but not conclusive research showsthat consumption of EPA and DHA omega-3fatty acids may reduce the risk of coronaryheart disease. One serving of [name of food]provides [x] grams of EPA and DHA omega-3fatty acids. (See nutrition information for totalfat, saturated fat and cholesterol.)
The recommended 6 ounces of fish per weekis designed to provide approximately 6,000mg (6 grams) of EPA with DHA per week (seethe chart on page 31).
A Caution for Pregnant andNursing Women
The Environmental Protection Agency(EPA) and the FDA advise women whomight become pregnant, are pregnant orare nursing (as well as young children) tomonitor the amount and type of fish theyeat to reduce exposure to mercury, a toxiccontaminant which can accumulate in thebody and cause harm, especially to thedeveloping fetus.
Concentrated amounts of mercury arehighest in older, larger, predatory fish.Women and children in the higher-risk groupare advised to avoid shark, swordfish, kingmackerel and tilefish altogether. They areadvised instead to eat a variety of seafoodlow in mercury such as shrimp, cannedlight tuna, salmon and pollock and to limitconsumption to 12 ounces per week.
Albacore white tuna is higher in mercury thancanned light tuna and should be limited to nomore than 6 ounces per week.
Other people not in the risk category areadvised to limit their consumption of shark,swordfish, king mackerel and tilefish to 6to 7 ounces per week. Eating a variety ofother fish is recommended to reduce thepotentially negative effects of mercuryand environmental pollutants such aspolychlorinated biphenyls (PCBs). Wheneverpossible, select wild or line-caught fish ratherthan farm-raised, because farmed fish mayhave higher levels of contaminants. In additionto receiving feed that may contain toxins,farm-raised fish also contain added colorings,antibiotics and other medicines to protectthem against disease spread in the crowdedfarm environment. There is also concern thatthe feed given to farmed fish to “fatten themup” might produce fish with more harmful fatsthat are not heart-healthy.
What If You Don’t Like Fish?
Supplementing With Omega-3s
If you don’t like fish or don’t eat it for other reasons, vegetarian sources of omega-3s (walnuts, canola oil, ground flax seeds and flax oil) are better than nothing, but you might also consider taking a fish oil supplement. The U.S. government does not have a general recommendation for Americans, but a few majorhealth organizations suggest an amount anywhere from ½ to1 gram (500 mg to 1,000 mg) of combined EPA/DHA per day, or3.5 to 7 grams per week. Good news: Fish oil supplements havelower levels of mercury than the fish itself, according to recenttests.
The American Heart Association does advise that patientswith documented cardiovascular disease consume 1 gram ofEPA+DHA daily from fish and supplements, when necessary.People with elevated triglycerides are advised to consume 2 to 4grams of EPA+DHA per day, taken in supplement form, under aphysician’s supervision.
Purchasing fish oils can be confusing since each capsule usuallycontains 1 gram (1,000 mg) of total fish oil, but the amountsof DHA and EPA vary. Many brands provide only 180 mg of EPAand 120 mg of DHA per pill. So, it may be necessary to take oneto three pills per day to receive a therapeutic dose. To minimizepossible indigestion or gastric upset from fish oil supplements,take them with a meal.
Another source of the omega-3 fat DHA are eggs from chickensthat are fed their natural diet (leafy greens, insects, worms) andspecial eggs from chickens fed a fortified diet that contains flaxseeds, fish oil or algae. They vary in the amount of omega-3 fats,which is usually printed on the label.
DHA supplements produced from a special algae are alsoavailable in pill form. Cod liver oil is usually not recommendedsince it may contain excessive amounts of the fat-solublevitamins A and D, which can be toxic. One concern regardingtaking large amounts of fish oil is its ability to thin the blood,which may be an issue for people with bleeding disorders,people taking prescription blood thinners such as Coumadin(warfarin) and those expecting to undergo surgery. Consult withyour diabetes care team and physician about supplementingwith omega-3s.
Note: 1,000 mg = 1 gram; 500 mg = 0.5 grams
Caution: Fish oil supplements can trigger potentially deadly heart rhythms in people with a history of abnormal heart rhythms according to a multi-center randomized study reported in the June 15 Journal of the American Medical Association. The 200 study participants all had a history of serious abnormal heart rhythms and had implanted defibrillators that shock a heart back into normal rhythm. During the study 65 percent of the participants who took fish oil supplements developedrhythm disturbances over a six month period, compared with35 percent in the placebo group. Researchers were not able toexplain this unexpected finding.
|EPA + DHA in 3-ounce serving (grams)|
0.5 grams = 500 mg
1.0 grams = 1000 mg
|Amount required to provide 1 gram of EPA+DHA per day|
|Salmon||0.7 to 1.8 grams||2 to 4.5 ounces|
|Herring||1.7 grams||1.5 to 2.5 ounces|
|Trout||0.8 to 1.0 gram||3 to 3.5 ounces|
|Sardines||1.0 to 1.7 grams||2 to 3 ounces|
|Halibut||0.4 to 1.0 gram||3 to 7 ounces|
|Catfish||0.2 gram||15 to 20 ounces|
|Shrimp, crab, lobster||0.2 to 0.4 gram||7 to 12 ounces|
|Source: Circulation, 2002;106:2747|
For More Information
The EPA has a Web sitewith links to state, territoryand tribal fish advisoryprograms. Go to http://epa.gov/waterscience/fish/states.htm and click on your state. You will beredirected to a site withlocal information. For moreinformation on fish andyour health, type “fish” intothe search box on theseWeb sites:
- American Heart Association:
- Food and Drug Administration: