Mayo Clinic Health Library

Omega-3 in fish: How eating fish helps your heart

Updated: 12-21-2010

If you're worried about heart disease, eating one to two servings of fish a week could reduce your risk of dying of a heart attack by a third or more.

Doctors have long recognized that the unsaturated fats in fish, called omega-3 fatty acids, appear to reduce the risk of dying of heart disease. For many years, the American Heart Association has recommended that people eat fish rich in omega-3 fatty acids at least twice a week.

But some people are still concerned about mercury or other contaminants in fish outweighing its heart-health benefits. However, when it comes to a healthier heart, the benefits of eating fish usually outweigh the possible risks of exposure to contaminants. Find out how to balance these concerns with adding a healthy amount of fish to your diet.

What are omega-3 fatty acids, and why are they good for your heart?

Fish contain unsaturated fatty acids, which, when substituted for saturated fatty acids such as those in meat, may lower your cholesterol. But the main beneficial nutrient appears to be omega-3 fatty acids in fatty fish. Omega-3 fatty acids are a type of unsaturated fatty acid that's thought to reduce inflammation throughout the body. Inflammation in the body can damage your blood vessels and lead to heart disease.

Omega-3 fatty acids may decrease triglycerides, lower blood pressure, reduce blood clotting, boost immunity and improve arthritis symptoms, and in children may improve learning ability. Eating one to two servings a week of fish, particularly fish that's rich in omega-3 fatty acids, appears to reduce the risk of heart disease, particularly sudden cardiac death.

Does it matter what kind of fish you eat?

Fatty fish, such as salmon, herring and to a lesser extent tuna, contain the most omega-3 fatty acids and therefore the most benefit, but many types of seafood contain small amounts of omega-3 fatty acids.

Most freshwater fish have less omega-3 fatty acids than do fatty saltwater fish. Some varieties of freshwater trout have relatively high levels of omega-3 fatty acids.

Are there any kinds of fish you should avoid?

Some fish, such as tilapia and catfish, don't appear to be as heart healthy because they contain higher levels of unhealthy fatty acids. Keep in mind that any fish can be unhealthy depending on how it's prepared. For example, broiling or baking fish is a healthier option than is deep-frying.

Some researchers are concerned about eating fish produced on farms as opposed to wild-caught fish. Researchers think antibiotics, pesticides and other chemicals used in raising farmed fish may have harmful effects to people who eat the fish.

How much fish should you eat?

For adults, at least two servings of omega-3-rich fish a week are recommended. A serving size is 3 ounces (85 grams), or about the size of a deck of cards. Women who are pregnant or plan to become pregnant and children under age 12 should limit the amount of fish they eat because they're most susceptible to the potential effects of toxins in fish.

Does mercury contamination outweigh the health benefits of eating fish?

The risk of getting too much mercury or other contaminants from fish is generally outweighed by the health benefits that omega-3 fatty acids have. The main types of toxins in fish are mercury, dioxins and polychlorinated biphenyls (PCBs). The amount of toxins depends on the type of fish and where it's caught.

Mercury occurs naturally in small amounts in the environment. But industrial pollution can produce mercury that accumulates in lakes, rivers and oceans, which turns up in the food fish eat. When fish eat this food, mercury builds up in the bodies of the fish.

Large fish that are higher in the food chain — such as shark, tilefish, swordfish and king mackerel — tend to have higher levels of mercury than do smaller fish. Larger fish eat the smaller fish, gaining higher concentrations of the toxin. The longer a fish lives, the larger it grows and the more mercury it can collect.

Pay attention to the type of fish you eat, how much you eat, and other information such as state advisories. Each state issues advisories regarding the safe amount of locally caught fish that can be consumed.

Should anyone avoid eating fish because of the concerns over mercury or other contaminants?

If you eat enough fish containing mercury, the toxin can accumulate in your body. It can take weeks, months or even a year for your body to remove these toxins. Mercury is particularly harmful to the development of the brain and nervous system of unborn children and young children. For most adults, however, it's unlikely that mercury would cause any health concerns.

Still, the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) recommend that these groups limit the amount of fish they eat:

  • Women who are pregnant or trying to become pregnant
  • Breast-feeding mothers
  • Children under age 12

Pregnant women, breast-feeding mothers and children can still get the heart-health benefits of fish by eating fish that's typically low in mercury, such as salmon, and limiting the amount they eat to:

  • No more than 12 ounces (340 grams) of fish in total a week
  • No more than 6 ounces (170 grams) of canned tuna a week
  • No amount of any fish that's typically high in mercury (shark, swordfish, king mackerel and tilefish)

Can you get the same heart-health benefits by eating other foods that contain omega-3 fatty acids, or by taking omega-3 fatty acid supplements?

The evidence is stronger for the benefits of eating fish rich in omega-3 fatty acids than for using supplements. However, people who have heart disease may benefit from supplements of omega-3 fatty acids and should discuss this with their doctors.

Other nonfish food options that do contain some omega-3 fatty acids include flaxseed, flaxseed oil, walnuts, canola oil, soybeans and soybean oil. However, similar to supplements, the evidence of heart-healthy benefits from eating these foods isn't as strong as it is from eating fish.