Eating a diet that includes a variety of seafood can be very good for your health. In fact, the American Heart Association recommends eating fish at least twice a week. Fish rich in omega-3 fatty acids can help prevent macular degeneration, cardiovascular disease, and a host of other illnesses. However, the mercury content in some fish can be dangerous to some high risk groups, so it's important to know which fish to avoid or limit in your diet.

Mercury actually occurs naturally in the environment. However, pollution contributes to the high levels of mercury. Mercury in the air makes its way into the water where it turns into methylmercury and is ingested by fish. The larger fish that live longer tend to have higher levels of mercury because they have consumed more mercury in their lifetimes.

Even though most fish and shellfish contain mercury, the FDA notes that it is not a dangerous issue for most individuals. However, it warns that high levels of mercury can damage the nervous system of children. Therefore, it's important that pregnant women (or those who may become pregnant), nursing mothers, and very young children limit their intake of seafood with a high mercury content.

If you don't fall into the high-risk group, you may want to limit your intake of mercury anyway because some studies have shown that high levels of mercury can affect fertility, blood pressure, and memory.

According to the FDA and EPA, king mackerel, shark, swordfish, and tilefish have the highest levels of mercury. In fact, they recommend that those with high risk exclude these fish from their diet. Others may want to limit their intake of these fish because the level of methylmercury may stay elevated for over a year.

Albacore tuna also has more mercury than other canned tuna, so the FDA recommends limiting intake of albacore tuna to six ounces per week. It also recommends limiting tuna steak to six ounces per week. Up to 12 ounces of lower mercury fish, such as shrimp, canned light tuna, pollock, catfish, and salmon, may be consumed per week.

Mercury is not the only concern when it comes to choosing fish, however. Some fish contain high levels of PCBs (polychlorinated biphenyls), dioxins, and other toxic environmental contaminants. Also, some fish should be avoided because they have been heavily fished, causing their numbers to be dangerously low.

The Natural Resources Defense Council maintains a list of fish with mercury levels and endangerment risks to help you choose wisely.

By following a few guidelines and eating a variety of foods, you can enjoy the many benefits of eating seafood while minimizing your risks.

This post was included in the 48th edition of the Weight Management & Fitness Forum.