International reports have consistently showed that mercury in certain types of fish may pose a danger to unborn babies. It has also been found that raw fish, such as the tuna and salmon used in sushi, can cause infections that may be detrimental to the foetus.
On the one hand, dieticians and nutritionists urge people to eat more fish. Fish, especially fatty fish, has a high omega-3 content which protects us from heart disease. It also assists in the development of the eyes, brain and nervous system before and after birth.
On the other hand, there have been reports that fish are contaminated with heavy metals, such as mercury, as well as dioxins and PCBs (polychlorinated biphenyls), which can be highly harmful to the developing baby. Sushi is also under suspicion as it may be contaminated with certain worms that could pose a health risk, particularly during pregnancy.
According to a recent edition of the Arbor Clinical Nutrition Updates (May, 2007), a number of new studies indicate that certain types of fish are more likely to be contaminated with mercury. The list includes swordfish, shark, marlin and tuna.
A Canadian study also found a link between attention deficit disorder (ADD) and the blood levels of mercury in children between the ages of 1.5 to 5 years. Chinese children living in Vancouver had the highest blood mercury levels and it is known that the Chinese population tend to eat more fish than their Caucasian counterparts.
This leaves dieticians with a dilemma: we need to find a balance between the well-established benefits of eating fish regularly in order to obtain the omega-3 fatty acids, and the potential danger of contaminants such as mercury and dioxins and PCBs that may be implicated in a variety of neurological problems, particularly in infants and young children.
At present, the South African Department of Health has not issued guidelines regarding the use of fish and fish products in this country. I, therefore, had a look at some of the guidelines that have been formulated in other parts of the world concerning fish intake.
According to the UK Food Standards Agency, pregnant and breastfeeding women can eat "most types of fish", but the Agency warns that certain types of fish should be avoided and the amount of other types of fish should be limited.
The UK recommendations for prevention of mercury exposure, state that shark, swordfish and marlin should be avoided, and that pregnant and breastfeeding mothers "should limit the amount of tuna they eat to no more than two tuna steaks (weighing about 140g when cooked, or 170g raw) or four medium-sized cans of tuna a week (with a drained weight of about 140g per can)."
Most people in South Africa do not eat shark, swordfish, or marlin regularly, so this recommendation should be easy to apply. However, many South Africans rely heavily on tuna (usually the canned variety) as a preferred type of fish and source of omega-3 fatty acids. The UK recommendation does, however, allow up to 4 medium-sized cans of tuna a week for pregnant and breastfeeding mothers, which should be more than enough for most users.
b) Dioxins and PCBs
To avoid contamination with dioxins and PCBs, the UK Food Standards Agency advises pregnant and breastfeeding women to avoid having more than two portions of oily fish (salmon, trout, mackerel or herring) per week. Oily fish tend to be more highly contaminated with dioxins and PCBs than fish with a low fat content (hake), which is why their intake should be limited to twice a week.
In South Africa, people tend to eat the above-mentioned fish. So, it is prudent to follow the UK Guidelines and to limit your intake when pregnant or breastfeeding to two portions per week. So-called "white fish", such as hake, can be eaten freely.
Australian and New Zealand guidelines
The Australian and New Zealand governments also published 'Recommended safe seafood consumption' guidelines in 2004 (Arbor Clinical Nutrition Updates, May, 2007). According to these guidelines, pregnant women and women who plan to fall pregnant, should only have 1 serving (150g for adults) of shark, billfish (swordfish, marlin), and no other servings of fish, during a period of two weeks.
This is a relatively strict guideline. The good news is that it's probably not applicable to the average South African who doesn't regularly eat these types of fish. In addition, the Australian and New Zealand guidelines say that pregnant and breastfeeding women can have 2 to 3 servings of any other seafood (which therefore must include tuna) per week.
It is, therefore, safe to say that the South African woman who is planning to fall pregnant, expecting a baby or breastfeeding an infant, can eat most seafood. However, she should not have more than four cans of tuna per week and should not have more than two servings of salmon, trout, mackerel or herring on a weekly basis.
If you regularly eat more exotic types of fish such as shark, swordfish and marlin, then you need to limit your intake drastically. Large predatory fish, such as swordfish, are at the top of the marine food chain, which means that they are more inclined to accumulate mercury in their flesh than smaller fish (e.g. the type of tuna that are caught for canning).
- (Dr I V van Heerden, registered dietician)
(Arbor Clinical Nutrition Updates, 2007. Mercury, fish and health. Issue 274, May. www.eatwell.gov.uk/asksam /healthydiet/fishandshellfishq/).