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Fish FAQ: The merits and hazards of eating fish
From MayoClinic.com
Special to CNN.com

Like many people, you're probably wondering which advice to take: Eat more fish because of the heart-healthy benefits of omega-3 fatty acids, or limit fish because of the risk of toxins, such as mercury. Toss in questions about farm-raised versus wild fish and the safety of the fish you catch, and the issue becomes even cloudier.

Before you avoid eating fish entirely, get answers to commonly asked questions about eating fish and the best way to safely include fish in your diet.

What are the health benefits of eating fish?

Fish is generally low in calories, saturated fat and cholesterol, making it a good overall substitute for poultry and meat. It's also a good source of protein and several vitamins and minerals.

Some types of fish, particularly fatty, cold-water fish — such as salmon, mackerel and herring — are also high in omega-3 fatty acids. Omega-3s appear to decrease the risk of coronary artery disease. They may also protect against irregular heartbeats and help lower blood pressure levels.

What are the health risks of eating fish?

As good as fish are for your health, be aware of potential downsides. Some types of fish may contain significant amounts of contaminants, such as mercury, polychlorinated biphenyls, dioxins or other chemical pollutants. Fish acquire these toxins from pollutants in lakes, rivers and oceans.

Bacteria, viruses, parasites or other disease-causing organisms also can infect fish in the same way that poultry and meat can be infected. The Food and Drug Administration (FDA) regulates the seafood industry and enforces laws and regulations to reduce the amount of potential hazards in the food. But these governmental regulations don't replace safe food handling. You need to safely store, prepare, cook and serve fish to reduce your risk of contracting food-borne illnesses.

What contaminant should you be most concerned about and why?

The major contaminant found in fish is mercury. This element occurs naturally in trace amounts in the environment. But industrial pollution can produce mercury that accumulates in lakes, rivers and oceans. Microorganisms in the water convert the mercury to a highly toxic form, called methyl mercury.

Large, predatory fish — such as tilefish, swordfish and king mackerel — tend to have higher levels of methyl mercury than do smaller fish because they're higher in the aquatic food chain. Small fish eat organisms that contain methyl mercury, and this contaminant is then stored in their bodies. 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.

If you consume fish that contains methyl mercury, the toxin can accumulate in your body as well. It can take weeks, months or even a year for your body to remove these toxins. Methyl mercury is particularly harmful to the development of the brain and nervous system of an unborn child and young children. For this reason, women who are pregnant or trying to become pregnant, nursing mothers, and children under 5 need to limit the amount of fish they eat. The FDA and the Environmental Protection Agency (EPA) report that for most people, however, the amount of mercury they consume by eating fish isn't a health concern.

What's the difference between farm-raised and wild fish?

The fish you buy in the grocery store is either caught in the wild — an ocean, river or freshwater lake — or raised on a fish farm. The location may pose some slight differences in health benefits and risks. Though farm-raised fish have similar amounts of omega-3 fatty acids as wild fish, they tend to have more total fat and calories. They may also have higher levels of contaminants due to toxins present in the feed given to fish. However, farm-raised fish are more readily available and often cost less. Commercially harvested wild fish usually have harvest limits set by state or federal governments, which may make them more costly. Fish-packaging companies in the United States are required to label consumer fish products as "farm-raised" or "wild." In addition to purchasing fish in a store, wild fish may be harvested for personal consumption by sport anglers.

Is it safe to eat what you catch?

The FDA regulates commercial fish and seafood to help ensure safety. But fish caught by sport angling aren't held to the same standards as fish caught commercially. Each state is responsible for protecting its residents from the health risks of eating wild fish caught for personal consumption.

Check advisories in your area to find out what types and how much fish is safe to eat. If no local advice is available, the FDA and EPA recommend that you limit consumption of fish from local waters to about 6 ounces a week.

How much fish is safe to eat?

Most people's fish consumption doesn't cause a health concern. In fact, most people don't get enough fish in their diet. The American Heart Association recommends at least two, 3-ounce servings of fish — preferably omega-3-rich fish — each week. For most, especially those at risk of heart disease, the omega-3 benefits of eating fish probably outweigh potential risks.

On the other hand, pregnant women and children need to limit how much fish they eat to avoid the harmful effects of mercury or other toxins. The FDA and EPA recommend that women who might become pregnant, pregnant women, nursing mothers and children should:

  • Avoid eating shark, swordfish, king mackerel or tilefish because they contain high levels of toxins.
  • Eat no more than 12 ounces a week of fish and shellfish that contain low levels of mercury — such as shrimp, canned light tuna, salmon, pollock and catfish. Canned albacore ("white") tuna has higher levels of mercury than does canned light tuna. For this reason, limit the amount of albacore tuna to 6 ounces a week.

What can you do at home to ensure food safety?

Even with many safety precautions in place, it's up to you to safely store, prepare, cook and serve fish. Follow these tips to ensure food safety:

  • Don't consume raw seafood, particularly raw shellfish.
  • Securely wrap fresh fish in a plastic bag or moisture-proof paper and store in your refrigerator.
  • Use fresh fish within two days, but preferably the day of purchase. Store frozen seafood no more than six months.
  • Defrost frozen seafood in the refrigerator just before cooking. For quicker thawing, place frozen fish in a sealed bag and immerse in cold water. Don't refreeze fish.
  • Wash hands, cutting boards and utensils with soap and water after coming in contact with fish.
  • Allow 10 minutes of cooking time for every inch of thickness for medium-cooked fish. To see if it's done, use a fork or the tip of a knife to cut into the flesh. The fish should separate into flakes and appear opaque throughout.

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  • July 14, 2006

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