This is one in a series of articles. For more on this subject visit The Daily Meal Special Report: Is Our Food Killing Us? Diet, Nutrition, and Health in 21st Century America.
Fish has long been associated with a healthy diet. It’s low in calories and rich in beneficial Omega-3 fatty acids. Whether we order fish off a restaurant menu or buy it at the fish market to cook at home, it is a popular and healthy meal choice. So, eat fish and be healthy, right? But there's a catch. Due to pollution and other environmental factors, some fish contain unhealthy amounts of mercury, PCBs (polychlorinated biphenyl), and parasites. In order to gain the health benefits of fish while avoiding the toxins and other dangers associated with it, it’s important to understand which types of fish we should be eating and how much is safe to eat.
How do toxins get into the fish? Chemical manufacturers and coal-burning industrial plants are the main source. These facilities release mercury into the air and rain washes it down into our rivers, lakes, and oceans, where interaction with anaerobic organisms converts it into methylmercury. Fish and shellfish absorb this toxin as they feed and it builds up in the tissue of the animal over time. Thus, the larger the fish, the higher its mercury content.
What are the risks to fish eaters from these substances? Methylmercury can damage the nervous system, immune system, and heart — but the greatest risk is to fetuses, infants, and young children. Pregnant or nursing woman who ingest even small amounts of mercury can pass on toxins to their fetus or infant. Children exposed to mercury in the womb or as an infant have been found to have altered memory, learning disabilities, lowered IQ, and impaired cognitive and nervous system functions in general.
PCBs are colorless, odorless chemicals that were once widely used in electrical equipment before they were banned in the U.S. in 1976. PCBs are highly stable and non-flammable, which made them popular for industrial purposes, but also means that they remain in the environment. About half of the 1.2 billion pounds of PCBs produced in the U.S. before 1976 are still present in air, land, and water — most of them in our rivers, lakes, and oceans.
PCBs settle into the sediments of bodies of water where bottom-feeding organisms ingest them and eventually transfer them to other the larger predator fish. PCBs have been found in fatty fish like lake trout, carp, and Chinook salmon with levels high enough to render these fish unsafe for human consumption in some cases. PCBs build up primarily in the fatty tissue of fish, leading to greater contamination in larger and fattier fish. Younger, leaner fish are safer. The health risks surrounding PCB include developmental problems in children, liver damage, and various forms of cancer. The highest risks are for fetuses and nursing infants.
The most prevalent source of PCBs today is thought to be farm-raised salmon. These salmon are fed with fish high in fish oil, with large amounts of fatty tissue, often full of PCBs. Some farmed salmon consume amounts of PCBs averaging five times the safe standard set by the U.S. Environmental Protection Agency (EPA). Based on these standards, the EPA recommends eating only one serving of farmed salmon per month.
According to FDA standards, “if you weigh 130 pounds, you should eat no more than four ounces of fish typically medium high in mercury (tuna, halibut, grouper, northern pike, bass) a week. If you weigh 170 pounds, then you can eat as much as 5.3 ounces a week.”
Jane M. Hightower, M.D., author of Diagnosis: Mercury, stresses that how much fish you may safely eat “depends on your weight, and the amount of mercury in the fish.”
“For the higher mercury fish such as swordfish, tile fish, king mackerel, and shark, you should not eat those at all if you are planning a pregnancy, are pregnant or nursing, or are a young child or infant,” Hightower adds. “For the rest of the population, these fish should not be consumed more than once per month.”
The American Heart Associated recommends that we eat at least two servings of fish per week, but recommends that pregnant and nursing women and young children should exchange shrimp, canned “light” tuna, Pollock, and catfish for fish high in mercury. (The FDA suggests that pregnant women and nursing women not cut out fish completely, as it contains important nutrients for a baby’s growth and brain development.)
On behalf of the Center for Science in the Public Interest and The Mercury Policy Project, an initiative of the Tides Center, Earthjustice filed a petition with the FDA in July 2011 to require signs in grocery stores and labels on packaged seafood products giving consumers information on the amounts of mercury in each product. To date, the FDA has failed to respond to the petition.
The FDA’s 2004 online advisory “What You Need to Know About Mercury in Fish and Shellfish” warns pregnant women and heavy fish eaters about the dangers of mercury, but lacks information on healthy seafood choices and alternatives, updated science on methylmercury exposure risk, and does not reach the general public, especially those without internet access.
Parasites are the other main danger associated with eating fish, mainly raw fish, which has become popular in dishes like sushi, sashimi, ceviche, and carpaccio. Raw saltwater fish can be a carrier of Anisakis simplex, a parasitic roundworm that invades the gastrointestinal tract of humans. This can cause mild to serious complications often difficult to diagnose. Diphyllobothrium is a tapeworm that has been traced to raw freshwater salmon. Since salmon lives in both freshwater and saltwater environments, it is susceptible to both kinds of parasites. Although sushi is made mostly from saltwater fish, gravlax is commonly made from freshwater fish, but is generally considered safe if it has been properly salted and smoked, or cured in a heavy brine.
Mackerel, squid, fluke, porgy, and sea trout are common carriers of Anisakis parasites and should never be eaten completely raw. Shrimp, eel, and octopus are carriers as well. Don’t bother inspecting your raw fish for a worm before you eat it, as it’s often the larvae that are ingested. Herring, which was once commonly eaten raw in The Netherlands, is another carrier. Since an outbreak of parasite poisoning in the 1980s, however, all Dutch herring must now be gutted immediately, then salted and frozen at four degrees Celsius below zero within 12 hours of being caught and for 24 hours thereafter. Similar regulations have been promulgated by the FDA, whose "parasite destruction guarantee" helps ensure that raw fish is safe to eat. The FDA’s Food Code recommends these freezing techniques to retailers providing fish that is intended to be consumed raw, however the term “sushi grade” is simply a marketing tool, and doesn't imply any necessary adherence to FDA guidelines. Some private suppliers have set up their own procedures to ensure that their products are safe.
So, should we stop eating fish? No. Fish is healthy and you should eat it to obtain the multiple health benefits, plus it is a delicious component to any meal. But be sure the make informed decision on the types of fish to eat and how often.
Emily Jacobs is the Recipe editor at The Daily Meal. Follow her on Twitter @EmilyRecipes.