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By Madelyn Fernstrom

Fish is one of the healthiest foods in nature, right? Or is it? While fish is often thought of as the perfect protein, ultra-lean, with loads of heart-healthy fats, the rising presence of mercury in some species causes many to limit or even avoid eating all fish. Should we be worried? And should groups at the highest risk for complications of mercury ingestion — pregnant women and children — just stay away?

A new article in Consumer Reports wants to clarify the issue, and make it easier to for consumers to decide how much and what kinds of fish to consume. What seems clear is that all consumers should avoid fresh fish with the highest mercury — tilefish, swordfish, shark, king mackerel, and also limit the consumption of higher-mercury fresh fish, including grouper, Chilean sea bass, halibut and tuna.

Solid albacore tuna is known to be higher in mercury, but there's a debate about the safety of light canned tuna for pregnant women.JEWEL SAMAD / Today

The health debate is now about the safety of canned tuna. It is well known that albacore (white) tuna is a higher mercury choice, and should be consumed in limited amounts. But “light” canned tuna, which has a lower mercury content, still remains approved by the FDA/EPA in limited quantities for pregnant women. Consumer Reports questions that decision, and recommends all tuna be avoided by this group.

A recent joint announcement from the Food and Drug Administration and Environmental Protection Agency recommends the consumption of 2-3 servings per week (about 12 ounces total) of low-mercury fish by pregnant women, including canned light tuna. Because fish is lean protein, low in saturated fat and naturally rich in omega-3-fats, with seafood also containing vitamin D and selenium, the overall evidence suggested to the FDA/EPA review panel that the health benefits of eating fish outweighed potential harmful effects from mercury.

The FDA and Consumer Reports agree that low-mercury fish like salmon, shrimp, pollock, tilapia, catfish and cod are a healthful choice.

Mercury is well-known to have toxic effects on the nervous system, and the levels in some fish have risen nearly 30 percent over the past two decades. And while there are strict recommendations for a “safe” limit of mercury levels in the blood, some experts believe that these levels are too high to support long-term health and should be lowered.

Salmon is a low-mercury fish that the FDA and Consumer Reports agree is safe to eat. Today

How much mercury is safe to consume without a health risk? 

This depends on body weight of the consumer. The higher the body weight, the more can be tolerated. That’s why children are at higher risk for mercury-related illness. And because of the developing brain and nervous system in the fetus, pregnant women are at particular risk.

As with all other foods in nature, moderation is key. For consumers, being mindful of the changes in the world’s fish supply is essential to making smart and healthier choices. Especially for pregnant women and children, choosing low-mercury fish in moderate amounts can be a health plus. But do your homework, and whether at home or in a restaurant, choose a low-mercury fish. There are so many low-mercury fish and seafood choices, this is hardly a daunting task.

As for omega-3 fats in pill form? That replaces only one healthful component of fish and is not an equivalent food exchange.