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How Long to Detox From Fish Before Pregnancy?

How many months does it take to clear 99% of the mercury and other industrial toxins from one’s body, and what role might our fat stores play in holding on to fat-soluble pollutants?

December 25, 2013 |
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Supplementary Info

Sources Cited

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D.-H. Lee, I.-K. Lee, K. Song, M. Steffes, W. Toscano, B. A. Baker, D. R. Jacobs Jr. A strong dose-response relation between serum concentrations of persistent organic pollutants and diabetes: Results from the National Health and Examination Survey 1999-2002. Diabetes Care 2006 29(7):1638 - 1644.

A. Wallin, D. Di Giuseppe, N. Orsini, P. S. Patel, N. G. Forouhi, A. Wolk. Fish consumption, dietary long-chain n-3 fatty acids, and risk of type 2 diabetes: Systematic review and meta-analysis of prospective studies. Diabetes Care. 2012 35(4):918 - 929.

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P. C. Dagnelie, W. A. van Staveren, A. H. Roos, L. G. Tuinstra, J. Burema. Nutrients and contaminants in human milk from mothers on macrobiotic and omnivorous diets. Eur J Clin Nutr. 1992 46(5):355 - 366.


Images thanks to harinaivoteza via Flickr. Thanks to Ellen Reid for her image-finding expertise and Jeff Thomas for his Keynote help.


Increased fish consumption of mothers before and during pregnancy leads to increased exposure to both mercury and the long-chain omega 3 DHA. Mercury may negatively affect brain development in one's unborn baby, whereas DHA may stimulate brain development. As we saw, though, the results of this study showed that the negative effect of MeHg outweighs the beneficial effect of DHA for most species of fish. Unfortunately, in the last two national surveys women of childbearing age--ages 18 to 45--were less aware and knowledgeable about this problem than other women, despite FDA and EPA campaigns to inform every OB/GYN and pediatrician in the United States about the potential risks of mercury in fish. But I wanted to highlight the "before." Not just during pregnancy, but even before one gets pregnant.

Since mercury sticks around, women may want to avoid polluted fish consumption for a year before they get pregnant in addition to just during pregnancy. The reason they suggest a year before getting pregnant is because the half-life of mercury in the body is estimated to be about two months. They fed folks 2 servings a week of tuna and other high mercury fish to push their mercury levels up, and then stopped the fish at week 14 and slowly but surely their levels came back down. I know a lot of moms are concerned about exposing their children to mercury containing vaccines, but if they ate just a serving a week or less of fish during pregnancy, the latest data shows their infants end up with substantially more mercury in their bodies than getting injected with up to 6 mercury containing vaccines.

But, with a 2-month half-life, within a year of stopping fish consumption your body can detox nearly 99% of the mercury. Unfortunately the other industrial pollutants in fish can take longer for our body to get rid of— a half life as long as 10 years for certain dioxins, and PBCs, and DDT metabolites found in fish. So to get that same 99% drop could take 120 years, which is a long time to delay one’s first child.

What do these other pollutants do? Well high concentrations of industrial contaminants are associated with 38 times the odds of diabetes. That's as strong as the relationship between smoking and lung cancer! Isn't diabetes mostly about obesity, though? Well these are fat-soluble pollutants, and so as people get fatter the retention and toxicity of persistent organic pollutants related to the risk of diabetes may increase, suggesting the shocking possibility that obesity may only be a vehicle for such chemicals. We may be storing pollutants in our spare tire like a hazardous waste dump.

Now the pollutants could just be a marker for animal product consumption—maybe that's why there’s such higher diabetes risk since more than 90% of the persistent organic pollutants comes from animal foods, unless you work in a chemical factory and stumble across some toxic waste. And indeed in the U.S. every serving of fish a week is associated with a 5% increased risk of diabetes, which makes fish consumption about 80% worse than red meat.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.

To help out on the site please email

Dr. Michael Greger

Doctor's Note

Mercury vs. Omega-3s for Brain Development is the study about balancing risks and benefits.

I explored how long it takes to get rid of some of the other pollutants in How Fast Can Children Detoxify from PCBs? PCBS are found most concentrated in fish and eggs (Food Sources of PCB Chemical Pollutants), which may be why there are lower levels of Industrial Pollutants in Vegans. This may also help explain the remarkable findings in Eggs and Diabetes.

The fact that we can still find DDT in Umbilical Cord Blood decades after the pesticide was banned speaks to the persistence of some pollutants. There’s a shortcut for moms, but it’s The Wrong Way to Detox.

More on the risks of mercury can be found in these videos:

For more context check out my blog: Top 10 Most Popular Videos from 2013

If you haven't yet, you can subscribe to my videos for free by clicking here.

  • DH

    Off topic (considerably), but does anyone know if horseradish containing “artificial oil of mustard” is bad for you?

    • Michael Greger M.D.

      The Material Safety Data Sheet on synthetic mustard oil can be found here:

      If you celebrate, Merry Christmas!

      • pmh

        Deigning to respond to irrelevant questions while some really pertinent ones go unanswered is rude. Get some manners, or I’m going to have to stop coming to the website to watch or read you. (I’ll just watch when you happen to show up in my youtube recommendations.) I don’t do “uncomfortable” for anyone, and your arbitrary and capricious responses are irritating. Bottom line: Either respond to everyone or no one. (And “Happy Holidays” fits everyone.) Happy Holidays!

        • Toxins

          PMH, there is a team of nutritionfacts volunteers (like myself) who can address questions you may have. It is impossible to address every question, and at one point early on in nutritionfacts Dr. Greger did do this. The popularity of the site has grown beyond what Dr. Greger can handle. Remember, is not his job, it is his side “hobby” done purely without profit and we should be grateful he has done this for the public good.

          • pmh

            Thanks for the civil response. I guess I haven’t been around long enough to have seen enough “volunteer” responses to notice your existence. All I’ve seen is video introductions by Gregor with entreaties to ask questions (to which I see plenty of responses with no answers). “Public good” is one thing, but so is the simple courtesy of answering questions you asked for. I don’t see that language in this post. Perhaps what I’m seeing is early posts that include out-of-date sentiment of pure solicitation (i.e., “please make me look successful by asking me questions!”). One can only hope.

          • Toxins

            You will notice that every so often Dr. Greger will dig deep and answer a question in depth in the link below.

          • pmh

            That link is helpful. I guess the true source of my irritation is having Dr. Greger introduce something really pertinent to my personal interests, have people bring up questions in the comments I’d also like answers to, and then – nothing. I see several “in depth” treatment of issues I might find answers or insight into in that link. Thanks!

          • VegAtHeart

            Fair enough about time constraints that limit the number of comments that Dr. Greger can directly respond to, but I would at least like to see in-depth responses to all comments and questions that legitimately challenge the accuracy of content provided by Dr. Greger’s videos.

            Dr. Greger has assumed the responsibility of being a messenger of the science of nutrition to the general public. Therefore, he should also be prepared to defend the accuracy of what he says and, where warranted, seek more information and provide clarification.

            As a recent example, I would like to see an acknowledgement and response to this recent thoughtful challenge by Darryl to Dr. Greger’s description of the mechanism by which nutritional antioxidants provide health benefits.

          • pmh

            You’ve expressed the precise logic behind the impetus of my original comment, albeit with slightly (that’s a joke) more restraint. Thank you!
            I apologize to you and anyone I offended by my less than PC bluntness. As I get sicker, time grows shorter and more precious. Nowadays my ability to tolerate even the smallest trifle is (I see) non-existent.

        • zapp7

          You’re the one in need of manners…

          • pmh

            Doubt you would know a grace if one bit you in the butt.

        • Richard

          Merry Christmas, Merry Christmas….And a Happy New Year….Too bad if you do not like it!

        • Thea

          pmh: Personally, I really appreciate that Dr. Greger responds when he can. I don’t consider it rude at all that he doesn’t respond to every question, especially when so many of the questions have already been answered. I would rather Dr. Greger spend his time on producing new content for this site.

          As for your, Happy Holidays, it is a myth that it applies to everyone. If you wish to be respectful of your fellow humans, you will be careful how you use it.

          • Eve

            For example, Jehovah Witnesses do no such celebrations.

        • Christo Okulian

          pmh: am so sorry, but by seeing your respond above. i know the issue is not in Dr. Greger and not from the NF team whose both i respect. they did good enough for whatever the can contribute in this area. you are not the only one that rarely be answered by Dr. Greger and by the team, me too, i ask many times but many times unanswered.. still i am okay with that. so be secure for your self whenever you find your question or someone’s question hasnt been answered for long. bottom line: the issue is on you including your happy holidays issue, u really need to check your “heart”, dont sweat such things. u wont get sick by such words.

          • pmh

            You should consider spending more time minding your own psychological and emotional health, and less on projecting your own illnesses onto the hearts and minds of perfect strangers.

          • Lloyd

            Irony of the century.

          • pmh

            The civil part of this conversation ended 4 days ago. Learn to read – or in your case – when to stop.

          • Birtee

            This saddening to some of us. Please let it end. Many of us have much greater life stress. Please don’t add to it here.

          • pmh

            Then stop contributing to it! Do you have a greater life stresser than end-stage progressive multiple sclerosis for which the only hope I now have of reclaiming some resemblance of a functional life after 30 years of failed traditional medicine is in some complex nutritional key to nerve regeneration hidden within the answers to some of these questions? Really people, I don’t give a fig about your opinion of my comment. You bring on your own stress by dwelling on stupid things. Get the bleep over it!

  • A

    Is it true that selenium binds with mercury and eliminates it out of the body? For those of us NOT trying to get pregnant but still having a few amalgam fillings, would it be helpful to eat 1-2 brazil nuts a day to eliminate the mercury out of our bodies faster?

    • Catherine J Frompovich

      In the Christmas spirit, may I offer this about mercury (Hg) and amalgam fillings. As long as a person has ‘silver fillings’, i.e., amalgams, in one’s mouth, mercury is still releasing and no amount of Brazil nuts a day would eliminate the mercury since the source is still emitting Hg. Assays on amalgams removed indicate that Hg releases from amalgam fillings over the time they are in the mouth. The indicator of that fact is this: Amalgam fillings are 50% Hg and 50% what’s called a eutectic mixture consisting of copper, tin, silver, and zinc, so there should be 50% Hg in the removed filling. Assays have indicated Hg content down from 50% to between 24 and 26%. The missing Hg either vaporizes or is abraded by chewing action.
      Many European countries long ago banned the use of mercury in dental fillings.
      The better part of discretion, I think, would be to have the amalgam fillings removed CORRECTLY by a dentist who is familiar with the proper procedure/protocol, and go on a detox program with proper supervision. Then you will be able to eliminate much of the mercury, if you don’t eat tuna, swordfish, mackerel and seafood, i.e., crustaceans, which are bottom dwellers that are subject to more pollutants.

  • John

    The video audio was 10% of the norm and impossible to hear. Is it possible to re-do re-issue, perhaps. The data is outstanding, helpful and invaluable. Pls continue. Merry Christmas to you as well!.

    • Richard

      Nothing wrong with the video, check your equipment…

  • DH

    Dr Greger,
    What is a good way to stay cognitively intact as we age, other than eating a plant-based diet? Are there specific foods you recommend (e.g. cocoa) that help to save off mild cognitive impairment and gradual cognitive decline?
    Many thanks and a fan of yours,

    • HemoDynamic, M.D.

      This is a very in-depth question. So the best way to get the answer to your questions is to use the search engine on this website.

      Here is the search I did for Cognitive Decline:

    • HemoDynamic, M.D.

      That is a very in-depth question. So the best way to get information to you inquiry is to use the search engine on this website.

      Here are the search results for Cognitive Decline:

    • Thea

      DH: I recommend Dr. Barnard’s book, “Power Foods For The Brain – An Effective 3-Step Plan to Protect Your Mind and Strengthen Your Memory” He also has a companion video, with less info, that is well done and perhaps worth sharing with trusted patients: “As seen on public TV: Protect Your Memory”

      • HemoDynamic, M.D.

        Yes this is also a good resource as well with lots of very helpful and useful info. thanks Thea! I hope you had a Good Christmas (If you celebrate it).

        • Thea

          Dr. HemoDynamic: Thanks for your nice note!

          I don’t happen to celebrate Christmas, but I appreciate your qualification and your well-wishes. I also have well-wishes for you! If you are in part of the world experiencing extreme cold, I also hope you are staying nice and warm. Take care.

    • Merio

      i think that the best way to protect the “mind” is to use it!! :-)
      Apart from the correct nutrition; logic/math games, meditation and having different kind of interests keep the mind smart and ready to learn something new everyday… IMHO obviously… even music could plays an important role in this issue…

  • Ronald Chavin

    Here are 7 scientific studies that indicate that fish eaters are not more likely to develop diabetes compared to people who don’t eat fish, thereby contradicting the 1 scientific study that Dr. Greger shared with us:

    Conclusion: Eating fish without any salt added will greatly lower our risk of developing cardiovascular diseases, stroke, all cancers, brain diseases, bone diseases, kidney diseases, any many other killer diseases without increasing our risk of developing diabetes. Because diabetics frequently die of cardiovascular causes, diabetics who eat fish (or swallow fish oil softgels) will live much longer than diabetics who become deficient in marine omega-3s.

    • Ronald Chavin

      According to the following scientific study, the people who ate too much white rice had a higher risk of developing type 2 diabetes:
      In this same study, the people who ate brown rice or other whole grains had a lower risk of developing type 2 diabetes.

      My hypothesis: People who eat fish tend to eat more white rice than people who don’t eat fish. Therefore, white rice consumption should be made an important confounding factor in all scientific studies that try to connect fish consumption with diabetes risk.

      In other words, people who always eat fish without white rice would have a very low risk of developing type 2 diabetes but people who always eat fish with plenty of white rice would have a very high risk of developing type 2 diabetes.

  • HereHere

    I’ve just read the transcript and the questions below. However, what I know about mercury is that is passes through the blood brain barrier (BBB). Too much causes Minimata disease (aka Mad Hatter’s disease), somehow interfering or damaging brain cells. So even though Mercury has a 2 month half-life in hair samples and blood, how do we know it isn’t accumulating in the brain? I suppose that once it passes through the BBB, it could pass out of the brain as well, but does anyone have any knowledge about this? My previous understanding was that mercury was bioaccumulative. Thanks!

  • Reuven Rosenberg

    It’s so frustrating that even the “healthy” foods are now dangerous.

    • Thea

      Reuven: Happily, the real healthy foods are plentiful. Eat whole foods in these categories: fruits, vegetables, whole grains, legumes, nuts and seeds. Wash them down with teas like green and hibiscus. All of those foods, in general, always have been and (based on our current knowledge) likely always will be healthy.

      It is only those questionable foods, like fish, which have been falsely promoted as healthy due to history and politics that appear to be switching sides. I completely understand the frustration. I just think it is worth putting into perspective.

      Good luck!

  • Carter

    I am a graduate student who will be attending medical school next fall. I am required to re-immunize for hep B after showing no resistance to it from the titter. I was hoping you would be able to provide options for the safest vaccines out there, not only for myself but for my children as well. Any help would be greatly appreciated.

  • Usc

    Does this imply that women should loose weight before pregnancy to prevent pollutants stored in their fat cells from releasing PCBs?