Is Eating Fish Safe? A Lot Safer Than Not Eating Fish! | Chris Kresser
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Is Eating Fish Safe? A Lot Safer Than Not Eating Fish!

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This is going to be a long article and I know not everyone will have time to read it. So I’m going to summarize the key points right up front because I think this information is so important:

Overview

  • Selenium protects against mercury toxicity, and 16 of the 25 highest dietary sources of selenium are ocean fish
  • If a fish contains higher levels of selenium than mercury, it is safe to eat
  • Most species of commonly eaten fish in the U.S. have more selenium than mercury
  • Fish are not significant sources of PCBs and dioxins when compared to meat, dairy or vegetables
  • The benefits of eating fish regularly far outweigh the potential risks, which are negligible
  • Pregnant mothers and young children should eat 2-3 servings of oily ocean fish each week

These days a lot of people are scared to eat fish. They’ve been told that fish are full of contaminants like mercury, PCBs and dioxins that cause neurological problems and may increase the risk of cancer. Pregnant women have been especially warned due to the supposed risk of these toxins to the developing fetus.

In the last few articles I’ve established the importance of the long-chain omega-3 fatty acids EPA and DHA in human health. I’ve argued that the conversion of plant-based omega-3 fats like ALA into the longer chain EPA and DHA is extremely poor in most people.

The conclusion is obvious: fish should be a part of our diet. But is it safe to eat fish?

You might be surprised to learn that the answer is a resounding yes. In this article I’ll demonstrate that concerns about toxins in fish have been overblown, and that there is almost no risk associated with eating fish when a few simple precautions are taken.

The selenium story

Although people are increasingly concerned about the effects of mercury levels in fish, recent evidence suggests that the trace amounts of mercury in the fish Americans eat aren’t high enough to pose a health risk.

But measuring only mercury significantly exaggerates this risk, because it ignores the important role of selenium.

Selenium is plentiful in many ocean fish species, but the public is unaware of its protective role against mercury. Selenium has high binding affinity for mercury. This means that when the two elements are found together, they connect, forming a new substance.

This new substance makes it hard for the body to absorb the mercury separately. Simply put, when selenium binds to mercury, mercury is not longer free to bind to anything else – like brain tissue.

Studies have shown that relevant amounts of selenium (Se) can prevent oxidative brain damage and other adverse effects associated with mercury toxicity. (PDF)

University of North Dakota researcher Nicholas Ralston has published several papers on the protective effects of selenium. He describes the relationship between selenium and mercury as follows:

Think of dietary selenium as if it were your income and dietary mercury as if it were a bill that you need to pay. Just as we all need a certain amount of money to cover living expenses such as food and rent, we all need a certain amount of selenium.

And guess what foods are highest in selenium? You’re right! 16 of the 25 best sources of dietary selenium are ocean fish.

He goes on:

Only one major study has shown negative effects from exposure to mercury from seafood, and that seafood was pilot whale meat. Pilot whale meat is unusual in that it contains more mercury than selenium. When you eat pilot whale meat it’s like getting a bill for $400 and a check for less than $100. If that happens too much, you go bankrupt. On the other hand, if you eat ocean fish, it’s like getting a check in the mail for $500 and getting a bill for $25. The more that happens, the happier you are.

What Ralston is telling us is that as long as the fish we’re eating has more selenium than mercury, there’s nothing to worry about.

Fortunately, studies by several independent organizations have consistently shown that most of the fish we eat contain significantly more selenium than mercury. Fish that contain more mercury than selenium include pilot whale, tarpon, marlin, swordfish and some shark.

The following chart illustrates the relative levels of selenium and mercury in commonly eaten ocean fish:

The selenium health benefit value (SeHBV)

Researchers have proposed a new measure of seafood safety called the Selenium Health Benefit Value (SeHBV) that takes the protective role of selenium into account.

Fish with a positive (above zero) SeHBV ratio would be safe to eat, whereas fish with a negative ratio would be unsafe. Using these criteria, most varieties of ocean fish have positive SeHBV ratios and are thus safe to eat.

A study conducted by the Energy & Environmental Research Center (EERC) and the Environmental Protection Agency (EPA) also found that an estimated 97% of the freshwater fish from lakes and rivers in the western U.S. are safe to eat. It is the only study I’m aware of that has measured both mercury and selenium levels in the tissues of freshwater fish. 1

So how much fish is safe to eat?

The joint recommendation for fish consumption of the EPA and FDA as of 2004 is as follows:

  • Eat up to 12 ounces (2 average meals) a week of a variety of commonly eaten fish and shellfish found consistently low in mercury, including shrimp, canned light tuna, salmon, pollock, and catfish
  • Limit albacore tuna to 6 oz. per week
  • Do not eat shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury

Notice that these recommendations are already quite liberal compared to the fish-phobes who suggest we avoid fish entirely.

But even these recommendations are too strict, because they don’t take the protective effects of selenium into account. As long as the fish is higher in selenium than it is in mercury, there’s no reason to limit consumption to 12 ounces per week.

What about dioxins and PCBs?

PCBs are synthetic organochlorine compounds previously used in industrial and commercial processes. Dioxins are organochlorine by-products of waste incineration, paper bleaching, pesticide production, and production of certain plastics. Yummy!

While it makes perfect sense to try to avoid these toxins to the greatest extent possible, abstaining from fish isn’t a particularly good strategy.

The highest dietary sources of PCBs and dioxins are not fish, but beef, chicken and pork (34%), dairy products (30%) and vegetables (22%). Fish constitute only 9% of our dietary intake of these chemicals.

The primary concern with PCBs and dioxins is cancer. Animal studies and some evidence in humans suggest that both are carcinogenic.

However, an analysis has shown that, per 100,000 individuals, consumption of farmed vs. wild salmon would result in 24 vs. 8 excess cancer deaths, respectively, while consumption of either farmed or wild salmon would result in 7,125 fewer coronary heart disease (CHD) deaths.

Another analysis of the same data suggested that, for all ages evaluated (25-35 to 85 years), CHD benefits outweighed cancer risks by 100- to 370-fold for farmed salmon and by 300- to more than 1000-fold for wild salmon.

It’s important to note that the benefits of fish consumption are based on prospective studies and randomized trials in humans, whereas estimated cancer risks include a 10-fold safety factor and are based on experimental data in animals and limited studies in humans at extremely high doses.

Cancer estimates also assumed lifetime salmon consumption of 1,000 mg/d of EPA & DHA (four 6-oz servings of wild salmon every week for 70 years). Of course virtually nobody in the U.S. currently eats this much salmon.

On the other hand, CHD mortality reduction may be achieved with lower intake (i.e. 250 mg/d – one 6-oz. wild salmon serving per week). At this intake, CHD benefits would be the same (7,125 fewer deaths) while lifetime cancer risk would decrease by 75% (6 and 2 estimated deaths per 100,000 for farmed and wild salmon respectively). The CHD benefits would outweigh cancer risks by more than 3500-fold in the case of wild salmon.

Once again, with few exceptions (the species of fish with more mercury than selenium), it’s not only safe but incredibly beneficial to eat fish regularly.

How beneficial? Let’s find out.

Fish consumption, cardiovascular disease and total mortality

In 2006 Mozaffarian & Rimm published a paper in JAMA called “Fish Intake, Contaminants and Human Health: Evaluating the Risks and Benefits“. They analyzed several studies that examined the impact of fish consumption on both coronary and total mortality. They found that modest fish consumption (e.g. 1-2 servings/wk) – especially of oily fish higher in EPA and DHA – reduced the risk of coronary death by 36% and total mortality by 17%, and may favorably affect other clinical outcomes.

The authors summarized their findings this way:

For major health outcomes among adults, based on the strength of the evidence and the potential magnitudes of effect, the benefits of fish exceed the potential risks.

And:

For women of childbearing age, benefits of modest fish intake, excepting a few selected species, also outweigh risks.

They also pointed out that the Japanese eat 900 mg/d of EPA & DHA on average, and have death rates from coronary heart disease 87% lower than those in Western populations (like the U.S.).

If you’re interested in learning more about this study, I recommend listening to the JAMA Audio in the Room interview with its lead author, Mozaffarian.

Fish consumption, pregnant mothers, and children

DHA is essential for proper development of the brain. It is preferentially incorporated into the rapidly developing brain during gestation and the first two years of infancy, concentrating in the gray matter and retinal membranes.

In a meta-analysis of 14 trials, DHA supplementation improved visual acuity in a dose dependent manner. In another trial of 341 pregnant women, treatment with cod liver oil from week 18 until 3 months postpartum raised mental processing scores at age 4 years.

This is consistent with observational studies showing positive associations between maternal DHA levels or fish intake during pregnancy and behavioral attention scores, visual recognition, memory, and language comprehension in infancy.

An FDA report issued in 2008 noted that the nutrients in fish – especially n-3 LCFAs, selenium, and vitamin D – could boost a child’s IQ by an estimated ten points. 2

The FDA report summarizes evidence suggesting that the greatest benefits to children would result if pregnant women of childbearing age, nursing mothers and young children ate more than the 12 ounces of fish per week currently recommended by the EPA.

According to the National Fisheries Institute, Americans currently consume only five ounces a week of fish high in n-3 LCFA, which is less than half the recommended amount. The NFI also estimates that up to 14 percent of women of childbearing age eat no fish at all, despite the fact that n-3 LCFA are essential to proper fetal brain and eye development.

Based on the new understanding of selenium’s protective role, and the importance of DHA for fetal and early childhood development, pregnant mothers should be advised to eat oily ocean fish regularly.

Fish consumption and autoimmune and inflammatory disease

The first evidence of the significant role of dietary intake of n-3 LCFA in reducing inflammation came from epidemiological observations of the low incidence of autoimmune and inflammatory disorders in a population of Greenland Eskimos compared with gender- and age-matched groups living in Denmark. The Eskimos in this study had dramatically lower rates of psoriasis, asthma and type 1 diabetes, as well as a complete absence of multiple sclerosis.

Animal and human studies suggest that n-3 LCFA suppresses cell mediated immune responses. Increasing the amount of n-3 LCFA while decreasing omega-6 fatty acids leads to improvements and a decrease of steroid use in patients with rheumatoid arthritis and asthma.

This is because omega-3s have been shown to suppress the capacity of monocytes to synthesize interleukin-1 (IL-1) and tumor necrosis factor (TNF). IL-1 and TNF are the principal mediators of mediation in several different inflammatory and autoimmune conditions.

Summary

This is simply a re-cap of the overview presented at the beginning of the article. But it’s worth repeating.

  • Selenium protects against mercury toxicity, and 16 of the 25 highest dietary sources of selenium are ocean fish
  • If a fish contains higher levels of selenium than mercury, it is safe to eat
  • Most species of commonly eaten fish in the U.S. have more selenium than mercury
  • Fish are not significant sources of PCBs and dioxins when compared to meat, dairy or vegetables
  • The benefits of eating fish regularly far outweigh the potential risks, which are neglible
  • Pregnant mothers and young children should eat 2-3 servings of oily ocean fish each week
  1. Energy & Environmental Research Center, University of North Dakota (EERC). EERC Research Finds Mercury Levels in Freshwater and Ocean Fish Not as Harmful as Previously Thought. June 22, 2009. Accessed at http://www.undeerc.org/news/newsitem.aspx?id=343
  2. Energy & Environmental Research Center, University of North Dakota (EERC). EERC Research Finds Mercury Levels in Freshwater and Ocean Fish Not as Harmful as Previously Thought. June 22, 2009. Accessed at http://www.undeerc.org/news/newsitem.aspx?id=343

148 Comments

Join the conversation

  1. Joe: good news for you.

    “Results from the first study, conducted jointly by the EERC, the U.S. Environmental Protection Agency (EPA) Western Ecology Division, and the University of Missouri’s Nuclear Reactor Center, show that an estimated 97% of the freshwater fish from lakes and rivers in the western United States are safe to eat. Conducted in 12 states in the western United States, it is the only study of this magnitude that has measured both mercury and selenium in fish tissue.”

    See full article here: http://newsletter.vitalchoice.com/e_article001496263.cfm?x=bfPRTnr,b7b1jv7h,w

  2. There isn’t any information on freshwater fish in this article, does this exist for selenium levels? I eat lots of freshwater fish, being from the upper midwest as well as an avid fisherman, and have always doubted the mercury scare tactics. Any information on this would be terrific!

  3. •Fish are not significant sources of PCBs and dioxins when compared to meat, dairy or vegetables
    •The benefits of eating fish regularly far outweigh the potential risks, which are neglible

    I like your blog and have learned a lot. But I’m having trouble with the two bullet points above. I”ve googled a March 2010 report stating that some fish oil brands, like TwinLab and Nature Made, have very high levels of PCBs, which apparently have no standards as to what consititute ‘safe’ levels! There was also a report two years ago from Michigan, I think, showing that high doses of fish oil caused late stage colon cancer in mice. The tumors took a mere 4 weeks to present themselves! Apparently, the anti inflammation properties of fish oil are so good that they also curtail the defenses against various intestinal bacteria, necessary to kill off cancer cells.

    I appreciate your fairness and tireless research, but I just don’t see where you have addressed these worrisome issues. Please advise and thank you in advance.

  4. Hi your site is greatly informative. I have listened to the podcast of Stephen Guyenet as well. But, I have to tell you I have been reading over Dr. Joel Fuhrmans’ site about to “eat fish or not”, it was enough to scare the daylights out of folks. Here it is…
    http://www.drfuhrman.com/faq/question.aspx?sid=16&qindex=6

    I always thought the good in fish outweighed the bad, especially after your articles. But now am wondering?? Hmm??? Or maybe Dr. F is not as informed….

  5. Thanks for the response.  My recollection from the movie is that the mercury levels were sky high.  I should have looked into it a bit further before posting here… wiki has an entry on the film and it seems that the mercury levels were overstated.  Though I’d still never eat dolphin.  🙂  Keep up the good work.

  6. Chris, I’ve got a question that’s eating at me.  I love sushi, and it would be great for me to believe it’s safer than I’d thought.  Your writing explanation about selenium being protective against mercury seems reasonable to a non-chemist like me, but I recently watched The Cove and it suggested that the high mercury in dolphin meat was having a horrendous impact on the people who ate the dolphins.  If the dolphins are eating (presumably) mostly fish that have more selenium than mercury, then why do they have such a high mercury content (to the point of making people sick)?  Is this a bogus claim in the movie or is it evidence that selenium doesn’t do as much good as you’re suspecting?

    • Perhaps because they concentrate the mercury. Pilot whale is another type of seafood consumed in some parts of the world that is higher in mercury than selenium – and I imagine it also eats mostly fish that are higher in selenium. I’ve not seen dolphin on that list, but that may be because dolphin is not commonly eaten in most parts of the world.

  7. Chris,
    I posted a short blog praising this article and your site on one of my blogs (http://dropoutnation.blogspot.com/2010/06/good-news-for-good-health.html) a couple of weeks ago.
    Today I discovered a comment by someone from Got Mercury leading me to a site with a mercury content calculator that seems to disagree with your findings.
    http://seaturtles.org/article.php?list=type&type=75
    I’m not altogether sure how to address this. I find your site highly informative and your research would seem to be impeccable while the studies they site are a bit less convincing.
    Any feedback from you would be appreciated since it is my intention to promote your site whenever possible.
    Thanks, Richard
    There is no way to Peace. Peace is the Way.

    • Richard,

      There’s nothing there that I haven’t already addressed, as far as I can tell. As I’ve shown in my articles, you have to consider the protective value of selenium. If the amount of selenium in a fish is higher than its mercury content, then there’s no safety issue. Fortunately, that’s true for most commonly eaten species of fish.

  8. I see.  Do you know of anyone who has endeavored to at least do some personal testing, in regards to fish consumption and mercury levels?  I really want to believe the selenium argument, but (in the spirit of this blog!), I am a bit skeptical.  The chart you highlighted from the Western Pacific Regional Fishery Management Council didn’t do much to quell my suspicions.  The last line of the paper (which was, incidentally, partially funded by the US Tuna Foundation and the Fisheries Scholarship Fund) is certainly true: “Consideration of mercury-selenium relationships in diet and tissues of exposed individuals will clarify risk:benefit relationships associated with fish consumption.”  Maybe that will be the Ralston’s next project (by the way, it’s remarkable that there seem to be no fewer than *three* Ralstons studying this topic…?  Two of the four authors of the paper, plus the other one you quoted in your post!).

  9. When mercury binds to selenium a new compound is formed, so I believe it wouldn’t show up on the tests.  However, mercury testing is a controversial area.  Some practitioners have pointed out that all of us have some level of mercury in our systems. The question is how much harm it’s causing, and whether it’s responsible for whatever symptoms you’re experiencing.

    • Do you know of any information on the cooking of fish and its effects on the EPA/DHA content?

      • I’d like to know this also. I have not found most fish oil supplements to be effective, due to rancidity or being denatured. I’ve never noticed benefit from eating fish, but have from a couple of the fish oil supplements I’ve taken. Wouldn’t cooking turn the fish oil rancid?

    • Hey Chris can you point me in the direction of those studies showing selenium complexing mercury? I can’t find any with such conclusive correlational findings.

  10. Chris,
    The idea that “Selenium protects against mercury toxicity, and 16 of the 25 highest dietary sources of selenium are ocean fish” sounds too good to be true!  After hearing many people recount stories of having their mercury levels tested, and coming away horrified with the results, I’ve drastically cut back on my fish intake…  which sounds like it might have been a mistake.  One point of clarification:  would one’s mercury level appear to be the same, regardless of whether or not the mercury had been detoxified by selenium?  Or does selenium physically change the nature of mercury, thereby lowering the amount shown in a test result?  I only ask because it was my impression that heavy metals, like mercury, take an extremely long time to dissipate once ingested.

  11. You did sorry, you’re right. The book looks like a good place to start. Thanks very much.

  12. An interesting article that addresses a real problem with some people. All the talk of eating fish being dangerous was putting me off, so thanks. It might be beyond the scope of this blog, as its a health blog, but would you consider talking about the sustainability of eating fish? That’s something that really worries me.

    • I mentioned in this article that sustainability is a real concern, and that choosing fish that are certified as safe by the Marine Stewardship Council is probably the best bet. I also recommended a book in the article if you want to learn more.

  13. Thank for such an informative article on the positives of eating Fish. Also it’s nice to read that, ” The highest dietary sources of PCBs and dioxins are not fish, but beef, chicken and pork (34%), dairy products (30%) and vegetables (22%). Fish constitute only 9% of our dietary intake of these chemicals.” Fish is favorite of mine and with the media attacking salmon, and even more farmed salmon, it was nice to read some more positive articles about my favorite food!
    Both Health Canada and The FDA have given farmed salmon the Green light. The demand for wild salmon is higher than the supply. With over fishing in our waters we need to take the pressure off wild salmon and turn more to farmed salmon.
    Thank you for this useful information
    Kind Regards,
    Molly W.
     

  14. Matthew,

    I know that shrimp and crab both contain selenium, but I don’t know the relative levels of mercury and haven’t seen studies comparing mercury and selenium. However, Ralston didn’t include them on his “don’t eat” list, so I’m assuming they are safe.  If you want to be sure, just increase your intake of other selenium rich fish and foods.

    There is an environmental consideration with shrimp harvesting, but that varies from area to area.  I don’t know the situation in Taiwan.

    • Hi Matthew and Chris,

      I’m also living in Asia, Mainland China, at the moment and I’m a bit worried of buying seafood from the local markets because of the effects of farming around here ie. chemicals, anti biotic use, pollution, etc.

      If you gather any useful information on seafood safety in Taiwan/China I would love to hear it.

      Thanks

  15. Once again, very informative. This whole selenium, mercury thing is very good to know. Have you heard anything about selenium/mercury levels in other kinds of seafood like shrimp, crab, octopus, etc… ? Also DHA and EPA levels? I’m living in Taiwan right now which has a huge seafood component to its diet so its cool to hear reassuring info about fish consumption. There’s also loads of other kinds of seafood so just curious if you knew anything about their safety.  I can’t imagine it being that harmful though when so many people eat it and have been doing so for quite awhile.  I guess the issue is with recently introduced harmful substances entering the food web but it still seems the benefits would outweigh any costs.
     

  16. I’ve never heard of anything like that, so I don’t really have any ideas.

    The best thing you could probably do is strictly limit omega-6 intake and take relatively high doses of flax oil and evening primrose oil.  The lower your omega-6 intake, the higher your conversion rates of ALA to EPA & DHA will be.

    I was going to suggest vegetarian DHA, but it’s made from marine algae so I doubt you’d be able to tolerate it.

  17. Great piece, there has been lots of information I didn’t fully comprehend in this series. But I have a follow up question: Do you have suggestions for people who are allergic to seafood? As a child I could eat seafood no problem, and miss it.
    However, I got mercury poisoning in chem lab in college, had chelation therapy, and ever since anything that comes from the ocean or lake makes me at best violently ill and at worst sends me to the hospital after a day or two of being unable to keep even water down.  Fish oil that’s been detoxed? Nope. Farmed fish that’s supposed to be mercury free? Nope. A bit of seaweed or fish stock used in food prep? Nope.  Frog legs (we used to catch them and cook them once or twice a week on summer vacation)? MSM/Chondrointin/Glucosamine supplements? Octopus or squid? No, no, no…
    I know I’m not getting proper ratios of Omega 3’s, but I have no idea how to fix this. Also, I really miss blackened salmon, tuna salad, sushi, crabcakes, you name it.  Any suggestions? (I should add I have auto-immune adrenal/thyroid disease, in treatment including added selenium, so that’s not the answer).

  18. Wow, great article. When I was researching what my ancestors ate,  the Welsh. Not only were they introduced to grains much later than everyone else, oats about 1,000 years ago, they also ate lots of salmon. It could be readily caught in the rivers and was considered poor peoples food, and some were known to eat salmon up to 4 times a week. A far cry from the modern diet, very radically different indeed.

    I always learn so much here, and it helps alot of pieces of the puzzle come together.  Thanks!

    • I found your article very informative. You make the statement: “Most species of commonly eaten fish in the U.S. have more selenium than mercury”.
      The question I have is, what about fish from Vietnam, China, etc? Finding fish that originates in the US is almost impossible!! I know that the US fish guidelines and specifications are much more in depth and that from other countries, but can they be safe to eat?
      Thanks.

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