Food for thought

By Kerry Stansfield

While pregnant, many mothers watch what they eat to ensure the best possible development for their baby. When I realised I was pregnant, I immediately cut out the obvious harmful substances from my diet and checked on the Internet to make sure there wasn’t anything I’d missed. But yes, there was quite a list. Much to my surprise it included some species of fish, such as tuna, due to the levels of mercury in their flesh. US FDA exposure standards recommend that pregnant women avoid certain highly contaminated fish like shark (meat and fins) and swordfish altogether, and limit consumption of certain other species to no more than 12 ounces per week. Luckily, most fish species contain very little mercury and it is recommended that women of reproductive age and children continue to eat fish such as Pacific salmon, flounder and haddock because of the nutritional benefits. To find out more about the levels of mercury in fish visit

Mercury is a global pollutant that cycle in the environment as a result of both natural phenomena and human activities. Mercury in the form of methyl-mercury is absorbed from seawater by plankton at the beginning of the food chain. Methyl mercury is not excreted and accumulates in the tissues of fish that eat the plankton. Fish such as big eye tuna, swordfish, and sharks live for a long time, accumulating chemicals from the many smaller contaminated fish they eat. The level of mercury in a fish depends on the species, its age/size and the waters from which it came.

Exposure of the fetus to low levels of mercury due to consumption of fish by the mother has been associated with subtle affects on neurological development of the fetus which may resemble learning difficulties later in life. Unborn babies are particularly vulnerable because their brains are developing very rapidly. A study of couples in Hong Kong found higher levels of mercury in the blood to be associated with infertility and that higher seafood consumption is associated with elevated blood mercury concentration (Choy et al 2002). So eating fish with high levels of mercury can also affect your fertility.

In addition to containing harmful mercury, many predator fish species are over fished and endangered. Some of the fishing methods used to catch them is harmful to non-target species. Longline fishing of tuna and shark also kills endangered sea turtles and albatrosses. The technique of shark finning (removal of the shark fin while the shark is still alive followed by the discarding of the rest of the shark) is cruel, wasteful and unsustainable.

There is certainly a lot of food for thought before you next order shark fin soup or tuna sushi, whether you are pregnant or not.

(Reference: Choy C.M.Y. et al (2002) Infertility, blood mercury concentrations and dietary seafood consumption: a case-control study BJOG: An International Journal of Obstetrics and Gynaecology 109 (10), 1121–1125.)