How Long to Detox from Fish Before Pregnancy?

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How Long to Avoid Fish Before Conception?

Mothers’ increased consumption of fish 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. However, the negative effect of mercury appears to outweigh the beneficial effect of DHA for most species of fish (see Mercury vs. Omega-3s for Brain Development).

Unfortunately, women of childbearing age appear less aware and knowledgeable about this problem than other women, despite FDA and EPA campaigns to inform every OB/GYN and pediatrician in the country about the potential risks of mercury in fish.

Since mercury sticks around in the body, women may want to avoid fish with high levels of mercury for a year before they get pregnant, not just during pregnancy. The rationale for avoiding fish for a year before pregnancy is because the half-life of mercury in the body is estimated to be about two months. In a study I profile in my video How Long to Detox from Fish Before Pregnancy a group of researchers fed subjects two servings a week of tuna and other high mercury fish to push their mercury levels up, and then stopped the fish. Slowly but surely their levels came back down (see the video for the graph). I know a lot of moms are concerned about exposing their children to mercury containing vaccines, but if they eat even just a serving a week of fish during pregnancy, the latest data shows that their infants end up with substantially more mercury in their bodies than if they were injected with up to six mercury-containing vaccines.

Given the two-month half-life of mercury, within a year of stopping fish consumption our bodies can detox nearly 99% of the mercury. Unfortunately the other industrial pollutants in fish can take longer for our body to get rid of. Certain dioxins, PCBs, and DDT metabolites found in fish have a half-life as long as ten years. So getting that same 99% drop could take 120 years, which is a long time to delay one’s first child.

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.

What effects do these other pollutants have? 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 associated with obesity though? Well, these pollutants are fat-soluble, so “as people get fatter the retention and toxicity of persistent organic pollutants related to the risk of diabetes may increase.” This suggests the shocking possibility that obesity “may only be a vehicle” for such chemicals.

Now the pollutants could just be a marker for animal product consumption, which may be why there’s such higher diabetes risk, since more than 90% of the persistent organic pollutants comes from animal foods. And indeed, in the U.S. every additional serving of fish a week is associated with a 5% increased risk of diabetes, which makes fish consumption about 80% worse than red meat. 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.

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

-Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.


Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.

8 responses to “How Long to Avoid Fish Before Conception?

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  1. Dr Greger- You are the best! I just gave a donation to help with your costs and I hope others will too! This information is so important and yet so sorely missing from most doctors and healthcare professionals. I really appreciate the work you and your team do for all of us who care about our health. Veganmom4girls

  2. Dr. Greger, Thanks for the work you do. How would you account for the fact that Paleo folks (Chris Kresser comes to mind) can trot out data that supports their view, so diametrically opposed to the vegan view?

  3. My research work was in prenatal and infant diet and nutrition, plus the role of detoxification prior to pregnancy in the late 1970s and early 1980s when I was studying for my degrees in natural nutrition and holistic health sciences. At that time I requested clients start a detox program 6 to 12 months before considering pregnancy AND that both partners, the intended mother and father, go on the detox program together at the same time. Many who could not conceive, after being in my program, conceived with no problem after the detox-nutrition program and their first try. I wrote the book, now out of print, Feeding Baby Naturally From Pregnancy On… I wish conventional nutrition and medicine, plus vested interests, would have taken more seriously we, who had been considered ‘quacks’ regarding natural nutrition, lifestyle changes and detoxification of chemicals back then and even now, instead of persecuting and prosecuting some of the MDs who saw the light long before MDs like Dr. Michael Greger, to whom I give a hat tip. Thanks for what you do, Dr. Greger; we need many more like you to change the insidious food/nutrition paradigm promoted by the food processing industries.
    Merry Christmas and Peace on Earth to all beings.

  4. Fish is bad for baby, but DHA, as you said, is “not even negotiable,” as a supplement or from seaweed because of its benefit to baby’s IQ and health. This could be used instead of fish. A source of mercury in America is in fillings. They are made of half mercury and every hot drink puts more of them in your blood stream, my opinion. Mothers with fillings should consider seeing their dentist or consult their prenatal doctor to diminish mercury evolution during pregnancy, such as with folate (beans, orange juice) or Amla as detox. Mercury is in fillings because silver does not melt at temperatures tolerable in the dentist chair. Filings are an amalgam made of half mercury, a dental filling is not much different than using soldering wire in your mouth, which also contains Mercury to melt at normal high temperatures. The more walnuts a mother eats the more DHA their is for baby. You also recommend DHA supplements, garlic, and one box of raisins a month. Anything to justify the beans!

  5. How Long to Avoid [Consuming] Fish Before Conception? As soon after one’s own conception as possible, for everyone’s sake, including the fish.

  6. One of the greatest lessons that parents can ever teach their children is that the lives of fellow creatures are not to be taken for granted; and animals in particular are not to be exploited. Therefore, parents should refrain as best they can from serving fish and other animal-origin foods to their kids, till they’re grown and on their own and can decide how they want to live — but hopefully having learned a beautiful lesson!

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