What’s so healthy about eating fish?
Fish is a high-protein, low-fat food that provides a range of health benefits. White-fleshed fish, in particular, is lower in fat than any other source of animal protein, and oilier fish contain substantial quantities of omega-3s, or the “good” fats in the human diet. In addition, fish does not contain the “bad” fats commonly found in red meat – called omega-6 fatty acids.
Are fish contaminated?
Despite their valuable qualities, fish can pose considerable health risks when contaminated with substances such as metals (e.g., mercury and lead), industrial chemicals (e.g., PCBs) and pesticides (e.g., DDT and dieldrin). Through increased testing, many of our oceans, lakes and rivers are now known to be surprisingly tainted. As a result, some fish are sufficiently contaminated that Environmental Defence recommends limited or no consumption.
Where do contaminants come from?
Contaminants enter the water in a variety of ways. Industrial and municipal discharges, agricultural practices, and storm water runoff can all deposit harmful substances directly into the water. Rain can also wash chemicals from the land or air into streams and rivers. These contaminants are then carried downstream into lakes, reservoirs and estuaries.
Fish take in these substances in several ways, and their contaminant levels depend on factors like species, size, age and location. Mercury, for example, is naturally converted by bacteria into methylmercury. Fish absorb methylmercury mostly from their food, but also from the water as it passes over their gills. Generally, larger and older fish have had more time to bioaccumulate mercury from their food and the water than smaller and younger fish. In addition, large predatory fish (like sharks and swordfish) near the top of marine food chains are more likely to have high levels of mercury than fish lower in marine food chains due to the process of biomagnification.
Fish can also absorb organic chemicals (such as PCBs, dioxins and DDT) from the water, suspended sediments, and their food. In contaminated areas, bottom-dwelling fish are especially likely to have high levels of such toxins because these substances run off the land and settle to the bottom. These organic chemicals then concentrate in the skin, organs and other fatty tissues of fish. Wild striped bass, bluefish, American eel, and seatrout tend to be high in PCBs, since they are bottom-tending fish often found in contaminated rivers and estuaries.
What are the risks of eating seafood contaminated with industrial pollutants?
Contaminants such as mercury, PCBs and dioxins build up in your body over time. Health problems that may result from eating contaminated fish range from small, hard-to-detect changes to birth defects and cancer. It can take 5 years or more for women in their childbearing years to rid their bodies of PCBs, and 12-18 months to significantly reduce their body burden of mercury. Mothers who eat contaminated fish before becoming pregnant may have children who are slower to develop and learn. Developing fetuses are exposed to stored toxins through the placenta. Women beyond their childbearing years and men face fewer health risks from contaminants than children do. Following the advice below will minimize your exposure and reduce the health risks associated with these contaminants.
What about mercury in canned tuna?
The two most popular types of canned tuna – white and light – vary greatly in their average mercury content. Canned white tuna consists of albacore, a large species of tuna that accumulates moderate amounts of mercury. Consequently, Environmental Defence recommends that adults and children limit their consumption of canned white tuna.
Canned light tuna usually consists of skipjack, a smaller species with approximately one-third the mercury levels of albacore. Therefore, Environmental Defence only recommends that young children (ages 0-6) limit their consumption of canned light tuna. However, recent news reports suggest that some canned light tuna actually contains yellow fin tuna, a species that is similar in size and mercury content to albacore. These products are sometimes (but not always) labelled ‘gourmet’ or ‘tonno’, and their consumption should be limited by adults and children. Overall, it’s best to exercise caution in how much tuna you (or especially your children) consume.
Do the health benefits of omega-3s outweigh the risks associated with contaminants in seafood?
There is no definitive answer to this question, but the information provided here can help you decide for yourself. For young children and women of childbearing age, consumption of mercury-contaminated fish can severely impact a child’s development. However, other sub-populations (older women and men) may find it an acceptable trade-off to exceed recommended seafood meal limits to increase their omega-3 intake. For our advisories concerning PCBs, dioxins and pesticides, the cancer risk (1 in 100,000 – the level recommended by the EPA) may not outweigh the benefits of omega-3s for people at high risk of cardiovascular disease. However, these chemicals are known to cause serious health problems besides cancer, so the trade-offs are not simple.
What about natural toxins in seafood?
Besides industrial pollutants and other human-made contaminants, some seafood may also contain natural toxins if fish eat harmful algae or bacteria. In warm tropical waters, a toxin called ciguatera can work its way up the food chain and be present in toxic levels in large, predatory fish. Cooking does not destroy the toxin, and consumption of ciguatoxic fish can cause intense flu like symptoms.
In addition, fish like tuna, mackerel, bluefish and mahimahi begin decomposing soon after capture. If not stored properly, they may develop histamine called scombrotoxin. Eating fish (even cooked fish) with high concentrations of scombrotoxin can cause an allergy-like reaction, which is treatable with an antihistamine.
Uncooked shellfish may contain disease-causing bacteria, viruses or parasites. Raw oysters, clams and other shellfish pose a particular risk since they are filter feeders – straining tiny particles from the seawater for food. If the seawater contains disease-causing microorganisms, these accumulate in the shellfish. The Norwalk virus, which causes intestinal illness in humans, is often associated with eating raw oysters and clams. For this reason, it is important to get raw shellfish from a reliable source, or ensure that your shellfish is cooked thoroughly.
How can I reduce the risks?
Fish consumption is the primary route of exposure to contaminants like mercury and PCBs. Since these substances can damage developing nervous systems and impair learning, seafood contamination is a particular concern for young children and women of childbearing age. The best ways to reduce exposure are:
- Reduce consumption of fish known to be high in contaminants.
- Prepare your fish in a way that cuts down on toxins.
- Eat sport fish from a variety of water bodies, and try not to eat the same species of fish more than once a week.
How can I cook fish to reduce toxins?
Unfortunately, there are no cooking methods that will reduce mercury levels in seafood since it binds to proteins in fish tissue (including muscle). However, levels of PCBs, dioxins and some pesticides can be reduced by the following cooking methods, since these chemicals build up in fatty tissue.
Before cooking, remove the skin, fat (found along the back, sides and belly), internal organs, tomalley of lobster and the mustard of crabs, where toxins are likely to accumulate. This will greatly reduce the risk of exposure to a number of hazardous chemicals.
When cooking, be sure to let the fat drain away, and avoid or reduce fish drippings.
Serve less fried fish. Frying seals in chemical pollutants that might be in the fish’s fat, while grilling, broiling or poaching allows fat to drain away.
For smoked fish, it is best to fillet the fish and remove the skin before the fish is smoked.
How can I avoid getting sick from eating seafood?
Check fish carefully before buying. Bruises, brown spots and cloudy eyes all indicate decomposition, and possibly bacteria. Buy fish that was frozen or refrigerated immediately after capture.
Cook fish and shellfish thoroughly. Handle raw fish as you would handle other raw meat products. Take care not to cross-contaminate cooked food or vegetables with the utensils used to prepare raw fish, and wash utensils and hands thoroughly in-between handling.
Avoid shellfish from untraceable sources, particularly if eaten raw.
What fish should I avoid?
Low-contaminant fish are an important part of a healthy diet, and Environmental Defense encourages people to include such fish in their diets, especially if they are caught or farmed in an environmentally responsible manner. However, there are certain species that people (especially women of childbearing age and children) should eat in moderation or avoid altogether.
What can I do to protect myself and my family?
You will need to detoxify these heavy metals and other contaminants using a heavy metal chelator, but a natural one that has been tried and tested during scientific trials called HMD.