Yes, fish can be a great dietary choice: It's lower in calories and saturated fat than red meat and naturally higher in healthful omega-3 fatty acids. But wait—it can also contain mercury and other potentially harmful contaminants. How are you supposed to balance those risks? Here's our answer to that and related questions.
Q: What are the benefits of fish?
A: Fish is the only food that directly supplies large amounts of the omega-3 fatty acids that have been shown to cut the risk of heart attack and stroke. Omega-3s may also elevate mood and help prevent certain cancers, cognitive decline, and eye disease. Most people can get enough by consuming fatty fish at least twice a week. Good choices include salmon and sardines, since they're also low in mercury. People who already have coronary heart disease require about a gram a day of those fatty acids, an amount that frequently requires taking a supplement. (Look for products labeled "USP Verified," which have been tested by the U.S. Pharmacopeia for purity and potency. Our Natural Medicine Ratings identify USP-verified products.)
Q: What are the risks?
A: Some fish, such as king mackerel, shark, and swordfish, are consistently high in mercury, which can harm the nervous system of a fetus or young child. Certain other fish, including canned light tuna, are also occasionally high in that metal. While the health effects of sporadic exposure are unclear, our fish safety experts think that women who are pregnant, nursing, or may become pregnant, as well as young children, should take special precautions. The risk posed by mercury in fish to other people is less established, though in general the heavier you are the more fish you can eat. Certain other contaminants sometimes found in fish, such as dioxins and PCBs, have been linked to some cancers and reproductive problems. While it's unclear whether the levels typically found in fish pose health effects, a few types may have lower levels of those pollutants. For example, some studies suggest that wild salmon may contain less mercury than farmed salmon.
Q: Is wild fish always better than farmed?
A: No. Some wild fish species, such as bluefish, tend to be high in PCBs. And although wild salmon is generally lower in PCBs than farmed, our tests suggest that some salmon labeled "wild" may have actually been farm raised. Your surest bet—especially in winter, when wild salmon is hard to find—may be canned Alaskan salmon. Ignore fish labeled "organic"; the U.S. Department of Agriculture has no standards for that. But you can check fish labels for country of origin and choose foods from countries you trust. That way, if there are, say, reports of prohibited antibiotics and suspected carcinogens in shrimp from China, as there were a few years ago, you can avoid those foods.
Q: Is sushi safe?
A: Sushi-lovers—particularly women of childbearing age—should choose pieces made with low-mercury fish, such as salmon or shrimp. Also make sure that the fish was frozen before serving, because that kills the parasites sometimes found in fish. (The Food and Drug Administration requires restaurants to take that step, though enforcement can be lax.) Make sushi at home only if you purchase frozen fish and prepare it right away, since home freezers typically don't get cold enough. In addition, practice good hygiene by washing your hands before and after handling the fish to help prevent the spread of bacteria.