Fish is a wonderful source of protein, low in saturated fat, and high in omega-3 polyunsaturated fatty acids, in particular EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid).  Omega-3 fats are considered essential fatty acids as the human body produces very little of these so they need to be consumed through food.  Fish is one of the few high dietary sources of omega-3 fats, a key reason for the recommendation of two servings of fish each week in the new Food Guide.

Omega-3 fats are heart healthy fats that may reduce the risk of cardiovascular disease by lowering triglyceride and LDL (bad) cholesterol in the blood.  They are also of great importance for pregnant and breastfeeding women and children, as they are essential in eye, nerve, and brain development.  DHA is particularly important during these times as insufficient amounts can affect a child’s vision and learning ability.

Mercury occurs naturally, as well as through mining, pulp and paper processing, and in the burning of fossil fuels and garbage. Small amounts of mercury are not harmful, however, large amounts can be harmful to both fetuses and young children, and can cause permanent nerve damage and delays in learning, speech, and movement.

Most fish do contain some amount of methylmercury, a form of mercury found in water.  The amount of methylmercury found in a fish is related to the level in its environment, as well as its position in the food chain.  For example, bigger predator fish (e.g., shark, swordfish) contain higher levels of methylmercury as they prey on smaller fish.  As well, the species’ lifespan also plays a role.  Lake trout have higher levels of methylmercury because they can live for a decade, where as Chinook salmon that only live for a couple of years typically contain lower levels. 

Because fish is such an excellent source of omega-3 fats, it is important to eat the two recommended servings per week.  Fish that are lower in mercury include all types of salmon, herring, tilapia, mackerel, pollock, trout, catfish, skipjack or yellowfin tuna (canned light tuna), and sardines.  It is recommended that children and pregnant and breastfeeding women choose these species as their two weekly servings.  Fish with high levels of methylmercury, such as king mackerel, shark, tilefish, swordfish, and fresh or frozen tuna, should be avoided by children and pregnant or breastfeeding women to stay within safe levels.  Since mercury can accumulate in the body, women who may become pregnant should eat these fish species no more than once per month. 

The good news is the Canadian Food Inspection Agency (CFIA) monitors the levels of mercury and other contaminants in our food supply regularly. Health Canada states that people who do not fall into the vulnerable groups listed above can safely enjoy one serving of higher mercury-containing fish per week.  Information regarding mercury levels of fish consumed by Canadians is available at: http://www.hc-sc.gc.ca/ or from the Ontario Ministry of Natural Resources at http://mnr.gov.on.ca/fishing/guide.html.

Written by Heather Stiles RD, as published in the Windsor Star, May 2007.