Dr. Tim Says...

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Dr. Tim Says....



One fish, Two fish, Mercury in Your Fish

Ingredients for making a fish soup

I had a patient ask about fish the other day. This was after I mentioned that with his risk factors for heart disease he would do well to eat at least two servings of fish per week. He responded that he was worried about the reports of "mercury and other stuff" in fish and wanted to know what to do.

First and foremost, there's no doubt of the tremendous health benefit in eating fish. There are hundreds of studies clearly showing that consuming fish high in Omega 3 fats reduces the risk of sudden death, death from heart disease and stroke. In a meta-analysis of numerous studies published in the Journal of the American Medical Association (JAMA 2006; 296: 1885 - 1898) Drs. Mozaffarian and Rimm conclude that eating 1 - 2 servings each week reduces the risk of death from heart attack by 36% and reduces total mortality by 17%.

Wow! Something easy, cheap and tasty to prevent disease and death. Count me in!

There is also evidence that consumption of fish or shellfish may prevent heart disease and progression of already established heart disease. Other studies have linked Omega 3 fats to prevention of certain types of cancers as well as heart rhythm problems. This research is not, however, as conclusive.

What about contaminants though? There is risk from heavy metals -- mercury being the most important and the most common. The health effects of mercury poisoning are mostly neurologic and involve such symptoms as numbness, tingling, difficulty thinking, problems with sensation and even paralysis. And there is some question of whether long term exposure to mercury can effect the heart.

The other main contaminant risk in fish comes from PCBs and dioxins. These are chemicals that were the byproducts of many manufacturing processes in the middle of the last century. PCBs have been banned since 1977. While dioxin release into the environment is still going on the levels of contamination have dropped. Research on animals shows that both of these chemicals may cause some types of cancers. There seems to be less risk from these contaminants and there are often higher levels of PCBs and dioxins in beef, chicken, eggs, milk and pork than in fish.

Mozaffarian and Rimm (and others) feel that that when the risks from contaminants are compared to the advantages of eating fish the evidence clearly shows that the benefit of including fish in your diet far outweighs any risk. As with anything one wants to reduce the risk and here are the guidelines that they feel will help you best: (These are along the guidelines of most health organizations based on the research as we know it.)

  • Eat 1 - 2 servings of fish per week.
  • Women of childbearing age should avoid fish that may contain higher levels of mercury.
  • Choose fish that are higher in mercury less often and make sure that you eat a variety of different fish.

Here's a list of common fish with the amount Omega 3 fats as well as the mercury content in parts per million (ppm) for a 3.5-ounce serving. The CDC recommends avoiding fish with more than 1.0 ppm.

Fish / Shellfish Mercury
PPM
Omega 3 fats
milligrams
Golden Bass (Gulf of Mexico) 1.45 905
Shark 0.99 689
Swordfish 0.98 819
King Mackerel 0.73 401
White Tuna (albacore) 0.35 862
Lobster 0.31 84
Halibut 0.25 465
Snapper 0.19 321
Mahimahi 0.15 139
Golden Bass (Atlantic) 0.14 905
Light Tuna 0.12 270
Atlantic Cod 0.10 158
Crab 0.09 413
Trout 0.07 935
Atlantic Mackerel 0.05 1203
Mussels <0.15 782
Anchovy <0.05 2055
Farmed Catfish <0.05 177
Atlantic Herring <0.05 2014
Farmed Salmon <0.05 2648
Wild Salmon <0.05 1043
Sardines <0.05 982
Clams <0.05 284
Oysters <0.05 688
Scallops <0.05 365
Shrimp <0.05 315

You can see that there are a lot of good healthy fish on this list with lower mercury content. It is clear from the research that the risk from contaminants is far less than the benefit from eating fish that is high in Omega 3 fats.

The take home message is to eat fish at least one or two times a week and eat a wide variety of fish and shellfish. The risk from "mercury and other stuff" is far outweighed by the benefit.

Timothy S. Harlan, M.D.
Dr. Gourmet
First posted: October 30, 2006 | Reviewed: July 24, 2017