Khursheed N Jeejeebhoy has reviewed the benefits and risks of a fish diet and should we be eating more or less?
Omega-3 fatty acids, eg eicosapentaenoic and docosahexaenoic acids which are plentiful in fish oils may preventing coronary artery disease. Eating three fish meals a week reduces risk in contrast to ineffectual high-fibre and low-fat diets did not have a significant reduction in mortality. Many trials have since shown the benefit of taking fish oil. This cardioprotective benefits is found with both wild and farmed fish.
. The consumption of as little as one fish meal weekly has been shown to be beneficial, with dose-dependent greater benefits up to about five fish meals per week.
The caveat to this simple diet change has been the suggestion of a risk of mercury poisoning of the central nervous system.
Mercury enters the atmesphere by combustion of waste and coal. The element then enters the oceans from the atmosphere where it is converted to methyl mercury by microorganisms and then taken up by marine life and concentrated in fish. As methyl mercury is not fat soluble, unlike dioxins, it does not accumulate in the fatty tissues. Methyl mercury is strongly neurotoxic.
The concentration of methyl mercury in fish b increased by fish eating other fish for food. Fish that are not predatory, such as sardines, salmon and shrimp, therefore have very low levels of methyl mercury. By contrast, predatory fish such as shark, tuna, swordfish and orange roughy have higher levels of methyl mercury. Farmed fish have the lowest levels of methyl mercury. Whilst methyl mercury per se is very neurotoxic, in fish methyl mercury is bound to cysteine, and this compound has a tenth of the toxicity of pure methyl mercury.
Whale meat is enriched with methyl mercury and is more neurotoxic..^
The conclusion is that in the amounts eaten in North America fish is very safe and the benefits large. That in pregnancy care should be taken with the eating o shark, tuna and sword fish.
Jeejeebhoy 2008, Benefits and risks of a fish diet-should we be eating more or less. Nature Gastroenterology and hepatology vol 5, pp 178-179

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