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Attack of the Tuna from Mercury!!

There are a lot of myths and misconceptions when it comes to food, diets, and general nutrition. It gets to a point where nutrition sometimes (erroneously, in my opinion) falls under the category of so-called CAM. I’ve seen bills from naturopaths, homeopaths and yes, even chiropractors that charge their client for some sort of nutritional counselling.

Ryan, a listener, recently sent us the following email:

Hey, there. Is there any truth to the following statement: “you should eat no more than 2 cans of tuna per week”? I normally eat 4+ cans of tuna a week as it is a cheap and delicious protein source. My tuna eating habits have made me the target of criticism from friends and family who tell me that I’m endangering myself by ingesting the mercury found in tuna.

I’ve read mixed things about the tuna issue and I’m really not sure what to think in this instance. I love my tuna, but I would be willing to cut back if there are any real health effects.

Thank you in advance! Your show kicks f’ing ass!

Ryan, you’re absolutely right, the show DOES kick f’ing ass. And now to your question.

Mercury is a naturally occuring substance that can be released in the air by means of industrial pollution. It falls and accumulates in bodies of fresh and salt water where it is turned into methylmercury. Methylmercury is what is absorbed and built up in fish as they feed in these waters.

Methylmercury hasn’t been linked to any neurologic or autoimmune disease, however it has been linked to increased risk of cardiovascular disease, including heart attacks, in healthy adults. Although there is still some controversy as to the levels of methylmercury in the diet that can lead to adverse effects.

And so, we turn to government safety guidelines which are, from what I can tell, very different depending where you live. For example, the FDA’s safety guideline is 1 part per million (ppm). In Canada, for some reason, our guideline is half that (0.5 ppm). A 2006 test of 60 random cans of albacore (white) tuna showed that 13% were above 0.5ppm where the highest one was 0.9 ppm. Still under FDA guidelines.

The “2 cans of tuna per week” saying was taken from an advisory made by the FDA and the EPA in 2004. The advisory was specifically targeted towards pregnant woman, nursing mothers and young children. It states that:

By following these 3 recommendations for selecting and eating fish or shellfish, women and young children will receive the benefits of eating fish and shellfish and be confident that they have reduced their exposure to the harmful effects of mercury.

1. Do not eat Shark, Swordfish, King Mackerel, or Tilefish because they contain high levels of mercury.

2. Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury.

- Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.

- Another commonly eaten fish, albacore (“white”) tuna has more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week.

3. Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but don’t consume any other fish during that week.

Follow these same recommendations when feeding fish and shellfish to your young child, but serve smaller portions.

You can get the advisory here.

Health Canada advises a maximum of 6 cans of albacore tuna per week. There is no advice on “light” (non-albacore) tuna because it doesn’t pose as much of a risk. So it seems that 4+ cans of tuna per week should be fine as long as you’re not pregnant, planning on being pregnant, breast-feeding, or a fetus.

6 comments to Attack of the Tuna from Mercury!!

  • An aside about heavy metals in food: According to ‘The Elements of Murder – A History of Poison‘ by John Emsley, we accumulate so much mercury in our bodies from our environment, that, by most world nutritional regulations for the amount of mercury allowable in meat for consumption, one in every ten people would be unsuitable as food for cannibals.

  • springer.adam

    ive heard that murcury is not the only heavy metal in tuna. is this true and if so do the suggested consumption guidelines take the other heavymetals and toxins within the fish?

  • larry coon

    So Mike…you’re saying that in order to be safe, tuna loving Canadians need to move to the U.S.?

  • larry coon

    P.S., I never know whether to include a tongue-in-cheek disclaimer.

  • dcardani

    Junk Food Science has a couple articles on this topic. This one is particularly interesting:

    http://junkfoodscience.blogspot.com/2008/01/fishy-sushi-scares.html

    It’s specifically about tuna used in sushi in New York city, but the money quote is here:

    All of the tuna it tested being sold commercially in New York had mercury levels nearly ten times below the lowest amount that has been shown might ever pose a danger to the most sensitive population (babies and children) with a lifetime of daily exposure.

    Note that last sentence – “a lifetime of daily exposure.” I think what she’s saying is you could eat it daily and it wouldn’t have any affect on you.

  • matt346

    I usually eat 6 to 9 tins a week so I hope I’m ok :)

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