The Benefits of Fish

A great way to introduce healthy eating to your diet is the addition of fish. There are many options and they are very rich in taste. So what are the benefits and what are the concerns?

In 1980 scientists identified that Greenland Eskimos had a low rates of heart disease. Since that time fish (finfish and shellfish) have been considered healthy. Several active constituents were identified that likely carried the health benefits: 2 long chain n-3 polyunsaturated fatty acids (n-3 PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Researchers also grew concerned over other active constituents, namely dioxins, and polychlorinated biphenyls (PCBs) present in some fish species. As a result public concern and confusion developed over the health benefits of fish consumption.

Disclaimer: All information provided should be considered as generalizations and not as specific information for any individual. Nor should this information be considered medical advice. This information needs to be considered in consultation with your family physician. Specific food allergies or medical conditions may make the provided information unsuitable for some individuals.

 A recent study known as a meta-analysis (a study that reviews the scientific literature on a certain topic, identifies all the studies performed, reviews them all and then combines the data using a statistically rigorous method to produce a more statistically powerful result then the individual studies themselves) was performed on the topic of fish intake and human health. Mozaffarian and Rimm published their findings in the Journal of the American Medical Association.

This rigorous study demonstrated that compared with little or no intake, modest consumption (250-500 mg/d of EPA and DHA) lowers relative risk of death from cardiovascular causes by 25% or more. In this study the total estimated cardiovascular risk reduction was calculated to be 36%. Interestingly, fish intake or supplementation above the moderate range added little or no additional benefit. This may explain, at least in part, why the rates of heart disease in Japan are so much lower then in comparable Western populations (the rate of death from heart disease is approximately 87% lower in Japan).

So finfish and shellfish have a clear strong benefit in reducing death from heart disease. There has been concern about the finding of elevated mercury levels in certain fish species. Two studies identified lowered reduction of heart protection with elevated mercury levels found in the fish studied. The net effect was still cardioprotective. With high levels of mercury there are serious concerns about neurologic effects particularly in children.

The real question being, as identified by Mozaffarian and Rimm, "the principal question may not be whether consumption of mercury containing fish increases cardiovascular risk but whether consumption of such fish would decrease risk even further if mercury were not present." The complications of mercury may be offset by the high selenium levels also found in fish but this interaction is poorly understood and requires further study.

Fish also contain Dioxins and PCBs (industrially produced toxins). These toxins are more commonly consumed in North America within beef, pork, chicken and dairy products. These toxic compounds have a demonstrated carcinogenic (cancer-causing) effect in animal studies and in humans. However, studies have demonstrated the benefits of reduction of heart disease (by the beneficial n-3 PUFAs) by far outweigh the risk of cancer associated with these toxic compounds. "[Heart] benefits outweighed cancer risks by 100- to 370-fold for farmed salmon and by 300- to more than 1000-fold for wild salmon".

In summary, this meta-analysis of fish consumption suggested 250 mg of EPA + DHA per day. At this level of intake the heart protective effects are most significant and the risks of associated toxicity are minimal. This can be converted to a weekly intake of 1500-2000 mg. This corresponds to one 6-oz serving/wk of wild salmon or similar oily fish, or more frequent intake of smaller or less n-3 PUFA–rich servings (see below chart).

"For individuals not keen on seafood smaller quantities of EPA and DHA can be found in salad dressings, cereals, and dairy products".

Interestingly, fish oil capsules contain 20% to 80% of EPA and DHA by weight (200-800 mg/g),  little to no mercury, and variable levels of PCBs and dioxins although they lack other potentially beneficial constituents such as protein and vitamin D.

For individuals with heart disease EPA + DHA intake of 1000 mg/day is recommended. "This could be approximated by one 6-oz serving/wk of fish richest in n-3 PUFAs (i.e., farmed salmon, anchovies, herring), more frequent consumption of other fish (see table below), or supplements".

Pregnancy Warning

"DHA appears important for early neurodevelopment.
Women who are or may become pregnant and nursing mothers should avoid selected species (shark, swordfish, golden bass, and king mackerel; locally caught fish per local advisories) and limit intake of albacore tuna (6 oz/wk) to minimize methylmercury exposure".

        In summary, eating 1-2 servings of the fish species described is a great way to introduce healthy eating into your diet. The benefits far outweigh the possible risks in scientifically rigorous studies.

All data and text in quotations from:

 Mozaffarian D., Rimm E.B., Journal of the American Medical Association, October 18, 2006—Vol 296;15:1985-1899.

Dr. Lawrence Korngut, M.D.
Chief Neurology Resident
London Health Sciences Centre
London, Ontario