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The Mercury Content of Fish

Fish has long been considered part of an athlete and “healthy” diet and there are many good reasons for this to be the case.  It’s a high quality protein and, depending no location and type, is generally inexpensive.  Low-fat fish is nearly fat free and higher-fat fish contains healthy w-3 fish oils.  At the same time not all is good in the land of fish due to the mercury content.

The Mercury Content of Fish

Mercury, as I imagine most know, is a toxic metal compound that, when it accumulates in the body, can cause a lot of problems.   Quite in fact, readers may have heard of the Mad Hatter syndrome which was actually caused by mercury being used by hatters back in the day.  The exposure caused them to go nuts.  It also gave us a great Batman villian.

The Mad Hatter

But that raises the question of how much fish can be safely consumed.    To address this, I’m simply going to excerpt the section on fish from Chapter 10: Whole Food Protein of The Protein Book where I examine fish protein and the issue of mercury content.

As you’ll see, depending on the type of fish in question, mercury can range from non-detectable to very low to exceedingly high.  And given the recommendations (at the end of the article) for daily limits to mercury content, it becomes clear that while some fish can be consumed in significant amounts daily, others are limited (e.g. 4-5 oz of canned tuna per day is about the limit even if bodybuilders and athletes often eat far more than that) and others exceed daily intake recommendations by far.

Fish

Fish is a high quality protein and many types of fish are extremely low fat, making it an excellent protein source choice. There are numerous varieties of fish and, similar to fowl, fish is appropriate at all times of the day except immediately around training. Of interest to dieting athletes, some research has found that fish keeps people fuller compared to either chicken or red meat (1).

Although fish is often chosen for its low-fat content, even the higher fat (typically cold water) fish typically contain most of their fat in the form of the omega-3 fish (w-3) oils.  These fats have a tremendous number of benefits, both for general health and athletic performance.

The beneficial effects of fish oils are numerous and include increased fat burning, decreased fat storage, decreased inflammation, decreased depression, mood stabilization, and decreased risk of heart disease and blood clots.

More benefits are being found constantly and it’s not an exaggeration to say that, if individuals were to take any single supplement on a daily basis, it should be a fish oil supplement.  Although food scientists are working to increase the w-3 content of other foods (such as w-3 eggs described below), fatty fish remain the primary source in the food supply.

However, counteracting the potential benefits of fish and the w-3 fatty acids, there is increasing concern over the mercury content of many types of fish; because of their place in the food chain, mercury accumulates in the tissue of the fish to varying degrees.

Chronic mercury exposure could potentially offset the benefits that fish might provide (1). Because of the potential health effects of mercury, both the United States Environmental Protection Agency (EPA) and the World Health Organization (WHO) have set daily and weekly limits for safe mercury intake.  Pregnant women, or women intending to become pregnant should minimize mercury intake from fish to avoid the possibility of birth defects.

A list of fish with their mercury concentration (in parts per million for a 3 oz serving) appears below.

Mercury Content of Fish

Source: Levenson CW and Axelrad D.  Too much of a good thing?  Update on fish consumption and mercury exposure.  Nutrition Rev (2006) 64: 139-145.

Lower numbers are better, indicating less mercury per 3 oz serving of fish.  On a daily basis, males should stay at the 0.19 level or less.  Fish with a mercury content higher than this can be eaten up to twice per week.

Females should stay at a level of 0.14 or less for daily consumption and can go up to 0.38 twice per week.

Orange roughy, a staple of some dieting bodybuilders, is far in excess of acceptable mercury levels for regular consumption.

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20 thoughts on “The Mercury Content of Fish

  1. Lyle,

    Great article. I guess I should stop eating a can of solid white albacore a day, huh? Could you please expound upon why fish is not an acceptable choice around workouts? Is this some quality of fish in particular, or is it that around workouts one should use more easily digestible protein sources, like whey?

  2. Depending on a host of factors and good old individual variability, whole food proteins too close to training tend to make people throw up.

    I have found that vomiting is generally not the best way to get an effective workout, hence my comment.

    However, this varies a lot and depends on the person (some train fine with food in their stomach, others don’t) and how long before the workout you consume the food. 30 minutes and 3 hours are both before workout but very different in terms of the potential for leaving undigested tuna fish on the floor of your gym.

    An additional factor is the type of workout that is being done. Low rep/long-rest strength training would be a different situation than metabolic type weight room work, cardio or intervals.

    The former is less of an issue with whole-foods close to training, the latter is a good way to taste your meal a second time when it comes back up.

    That particular comment makes more sense w/in the context of the chapter/book it came from which is why it seems a bit unclear.

    Lyle

  3. As always, thank you for the hasty and thorough answer.

  4. Good article – but we have to remember that it can heavily depend on a brand too. Some time ago, I’ve found interesting data about the mercury content in canned tuna in Poland (it’s not ppm, it’s mg/kg – it doesn’t matter, because the differences are quite significant anyway!)

    mg/kg

    Lisner 0,028
    Graal 0,033
    Heinz 0,054
    Laguna 0,054
    SuperFish 0,078
    Rio Mare 0,081
    Neptun 0,124
    King Oscar 0,131
    Abba 0,295
    Łosoś 0,376

    As you can guess – the better than brand, the higher the price, the lower the content of mercury is. I hope.

  5. “mercury concentration (in parts per million for a 3 oz serving)”

    Those units don’t make sense. You must mean something like “amount per 3 oz serving”, where amount can be # of atoms, mass, etc. “Parts per million” is already dividing by serving size.

    I trust that the acceptable limits are stated in the same units, so as long as the “per 3 oz” is right, I can use that.

    Why are higher amounts acceptable twice weekly? Is there some natural process that clears mercury, making it something other than purely cumulative?

  6. Wow. you wrote the article already. I didn’t expect it so soon.

    I’m a bit surprised at some of the levels listed, as I had it in my mind that shellfish often had higher levels. I’m also pleasantly shocked to find that wild Alaskan salmon is indeed one of the lowest ppm of mercury. thank-you for that tidbit, for it’s my favorite fish.

    Some fish commonly used for Sushi does/did exceed 1ppm, especially the large tunas, which is quite sad, but that was 1994 data, and your data is much more recent.

  7. Ok, so I’m looking at the paper and the chart where I pulled the above data. They list the fish under the heading of “Fish 3 oz serving Mercury Limit”. And then list mercury in parts per million. No further explanation of it is given.

    As to the twice per week thing, the ‘and’ in that sentence should be an ‘or’ which explains the confusion. Basically, if someone only ate fish twice per week, they could use the higher value. If they eat it daily, use the lower one. Sorry for the confusion, that’s another typo I need to fix in the book.

    Quoting from the paper
    “It also makes separate calculations for mercury in daily compared with twice-weekly fish consumption.”

    basically, it’s either the lower value daily or the higher value (but you can only eat mercury containing fish twice per week).

    Lyle

  8. Good stuff. I used to eat a ton of tuna with no issues (that I knew of at that point)….but have stopped that for many years. Switched to salmon, sardines and herring. Now if I have a can of tuna I get a migraine….interesting, perhaps I was able to reset my sensitivity to mercury, as it tends to settle in the brain.

  9. Lyle,

    While it should still be monitored, is mercury a bit less of an issue if regularly using a far infared sauna for detox purposes? Obviously too much mercury would eventually become a problem anyway, but I’m curious if this can have a mitigating effect to some degree.

  10. TJ

    Couldn’t tell ya’ since I know nothing about them.

    Lyle

  11. Piecing together bits of information here & there from online, essentially word of mouth, I can put together the following.

    The kidneys and the brain seem to filter most of the mercury out from the blood, so the blood tends to measure considerably less mercury levels in ppm than does the hair or the urine.

    Half-life of mercury in the blood has been estimated as about 3 days, mercury in body tissues clears slowly, with a half-life of about 90 days, and mercury in the brain and central nervous system clears incredibly slow, with a half-life of 15 to 30 years.

    Taking intravenous or oral chelates seems to be the normal accepted manner of getting rid of heavy metals in the tissues, and it’s said to work for the brain as well. Alternative health approaches have advocated safer heavy metal cleanses for years, but I don’t know of any research. I found claims and denials that sauna helps rid of heavy metals, so that’s a wash. Even if it did, would probably need to take supplements to try to keep the newly circulating mercury from settling in the brain.

    The above charts seem to indicate a maximum daily mercury intake of about 16 µg/day for men, which matches the WHO recommendation, but it is a little over 2x what EPA/FDA recommends.

    The World Health Organization 2002 guideline is 1.6 µg/kg/week and converted to a daily dose for comparison is 0.228 µg/kg/day, or 16 µg/day of methylmercury for 70kg man.

    It appears that some time after 1998, EPA dropped the recommended daily intake from 30 µg/day to 0.1 µg/kg/day, or 7 µg/day for a 70kg person.

    The only recent information I can find from the FDA was to say eating fish has health benefits, but but it limits women who may become pregnant to 12 ounces of low-mercury fish per week.

    A University of Rochester study supported the previous EPA/FDA recommendations of 30µg/day in 1998, which was close to the WHO recommendations at that time.
    https://www.rochester.edu/pr/releases/med/mercury.htm

  12. After I thought I was done reading up on mercury, I ran across the EPA data I was originally looking for.

    https://www.epa.gov/iris/subst/0073.htm

    The following bit explains the EPA’s reason for not fully using the University of Rochester study (Seychelles Islands). U of R felt that the Seychelles Islands study was more applicable to American diet than the Faroe Islands study, but EPA followed the safe route, which is… well, safe.

    ###
    Two of the studies (Faroe Islands, New Zealand) reported effects on a number of neuropsychological endpoints, whereas the third (Seychelles Islands) reported no effects related to in utero exposure to methylmercury. Benchmark dose analysis of a number of endpoints from both the New Zealand and Faroe Islands study converged on an RfD of 0.1 µg/kg-day, as did the integrative analysis combining all three studies.
    ###

    Overall, I’m quite happy with information you presented, and it’s in line with what the rest of the world is using as reference. EPA seems to have dropped the current levels due to the perceived effect on the most susceptible population, which are pregnant mothers and young children, which I assume isn’t your target audience! =-)

  13. Lyle: Have you looked at the effect of selenium yet?

  14. The popular orange roughy recommendation by bodybuilders is a total mystery to me. Not only is it the most contaminated fish, it only has .001g of DHA/EPA per 3oz serving. And its EXPENSIVE!

  15. While mercury levels over 50ppm appear to be definitely detrimental, it is likely that the effects of at “low” levels of mercury are overstated. Three major studies found either no or minor effects, of mercury at levels up to 20 times the average level of the US general population.

    Please see below for further reading

    https://whyfiles.org/201mercury/3.html

    At what level does mercury become harmful?
    The World Health Organization’s guidelines maintain that the lowest level that could possibly be harmful to humans is 5 parts per million (ppm). This level is based on scientific results from the 1960s that placed the level at which risk begins at 50 ppm for most people; WHO then applied a safety factor of 10, deciding that a level of 5 or less is safe for even the most vulnerable populations.
    Now the University of Rochester team has conducted an extensive study in the Seychelles Islands of the most sensitive population — young children — where the average level is about 7 ppm, about 10 times the level of the U.S. population. The scientists found no harm from mercury at levels up to 15 ppm, nearly twice the average Seychelles level and about 20 times higher than the average U.S. level.

  16. FDA chart “Mercury Levels In Commercial Fish and Shellfish”

    https://www.fda.gov/food/foodsafety/product-specificinformation/seafood/foodbornepathogenscontaminants/methylmercury/ucm115644.htm

    SALMON (CANNED) * 0.008 ND 0.017 ND 0.086 34

    Alaska canned salmon FTW.

  17. I recently read your article on fish oil dosage which gives 10x1g pills a day for a general guideline. Now on my bottle of fish oil pills it says “Mercury is below a limit of 0.1 ppm”. So if I take 10 a day, that is 1 ppm of mercury daily which seems very high relative to the chart you provided. Should I be concerned??

  18. I am skeptical about the benefits of omega 3 oil found in most commercial canned fish products. Omega 3 fatty acids are classified as polyunsaturated fats. These fatty acids are likely to undergo reduction when cooked at higher temperature, given their relative oxidative stabilities. With the manufacturing practices of canned fish products, it can be assumed that the omega 3 fatty acids are likely to be rancid, as a result of the cooking process. Therefore the quality of omega 3’s found in canned fish products seem questionable. Lyle, what are your thoughts on this?

  19. What makes you think fish oils are produced via cooking?

  20. He doesn’t think fish oils are produced via cooking, he’s concerned about whether fish oils are broken down by heat.

    To Danny: as far as rancidity, canned fish is not rancid. Rancidity requires oxygen, and the inside of a can is oxygen-free and very stable.

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