Pregnant? For Your Baby's Health, Eat Fish, But Make Sure It's High in Omega-3 and Low in Mercury

child brain development

Story at-a-glance

  • Omega-3 fat is critical for healthy development in utero, especially for eye and brain development. The ratio of omega-6 to omega-3 is also important for proper development. Ideally, it should be less than 5:1
  • Animals fed a diet in which the omega-6 to omega-3 ratio matched the standard American diet (high in omega-6, low in omega-3) produced offspring whose brains were much smaller than those fed ideal amounts
  • In a second study, pregnant women who ate 600 grams (21 ounces, or about 4 servings) of fish per week during pregnancy had children whose IQ scores were 2.8 points higher than those who ate less fish


This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.

By Dr. Mercola

Omega-3 fat is important for proper energy storage, oxygen transport, cell membrane function, and regulation of inflammation. It's also critical for healthy development in utero, especially for eye and brain development, and plays a role in the length of gestation.

Recent research has again confirmed the importance of omega-3 fats during pregnancy, and the danger of too much omega-6. The former you get primarily from fish, whereas processed vegetable and seed oils — staples in the standard American diet — are the primary sources of the latter.

The ideal ratio between these two essential fats ("essential" meaning your body cannot produce them, so you have to get them from your diet) is 1:1, but a processed food diet provides FAR more omega-6 than omega-3.

Unless you avoid vegetable oils and either eat plenty of fish or take a high quality omega-3 supplement, you may be getting around 16 times more omega-6 than omega-3 from your diet.

As one recent animal study1 shows, such a lopsided ratio during pregnancy can have severe health consequences for your baby.

Another Major Concern With Your Oils

Another major factor that has contributed to a large percentage of the amount of chronic disease present in Western nations is the introduction of refined vegetable oils.

Prior to 1900, the average intake of vegetable oils was less than a pound a year and in 2000, that had increased to 75 pounds per year. We simply never had the ability to consume this much vegetable oil prior to food processing.

Refined oil contributed to the massive distortions in the omega 3:6 ratios. There is nothing intrinsically wrong with omega-6 oils if they are consumed in their native form, which is typically in unrefined seeds and nuts.

The key take-home point is to avoid virtually all refined vegetable oils. Not only do they allow you to overconsume them but they are also highly susceptible to oxidation and are typically damaged by the time you use them.

I personally consume about 10 to 15 grams of omega 6 oils a day but not one microgram is refined. They are all in the form of seeds and nuts that I eat raw, or freshly grind them immediately prior to eating.

I also eat about 4 ounces of clean fish a day in the form of wild Alaskan salmon, sardines, or anchovies. That and my seeds give me nearly 10 grams of omega-3 fat a day so my omega 6:3 ratio is about 1.5:1.

Lopsided Omega-3 to Omega-6 Ratio Harms Brain Development

In the featured study,2 animals fed a diet in which the omega-6 to omega-3 ratio matched the standard American diet produced offspring whose brains were much smaller than those fed equal amounts of omega-3 and omega-6.

Once the offspring reached adulthood, they also developed emotional problems, exhibiting greater levels of anxiety. This despite eating a healthy diet from birth, onward. As reported by Medical News Today:3

"The team performed the first comprehensive measurement of lipid metabolites in the developing brain; they identified that metabolites of omega oils are vital regulators of neural stem cells — the cells that go on to develop into fully fledged brain cells.

In the rats with diets heavier on the omega-6 than 3, the neural stem cells developed more rapidly, to their detriment. The results ... show that increased levels of omega-6 produce an increase in omega-6 oxides. These omega offshoots cause premature aging of fetal neural stem cells.

The study's authors conclude: 'These findings provide compelling evidence that excess maternal consumption of omega-6 combined with insufficient intake of omega-3 causes abnormal brain development that can have long-lasting effects on the offspring's mental state.' [Emphasis mine]

Fish Consumption in Pregnancy Linked to Better Brain Health

A second study4,5,6 strengthens the argument by showing that the brain benefits of omega-3 appear to outweigh many of the hazards associated with mercury exposure.

Here, the researchers looked at 2,000 pregnant women, who reported their seafood intake — including the specific species of fish — via food questionnaires, starting in their first trimester. On average, the women ate about three servings (500 grams) of fish per week during pregnancy.

At birth, the umbilical blood was assessed for omega-3 DHA, mercury, and PCBs. The children underwent cognitive tests and autistic spectrum disorder evaluation at the age of 14 months and again at age 5.

The results showed that:

  • Higher fish consumption during pregnancy was associated with increased cognitive scores, and decreased risk of autistic symptoms in the children
  • For every additional 10 grams of fish per week over 500 grams, there was a corresponding improvement in test scores
  • Eating 600 grams (21 ounces, or about four servings) of fish per week was linked to a 2.8 point increase in IQ score. This link was particularly strong for large fatty fish, including tuna, even though tuna also has some of the highest levels of mercury
  • Fish intake during the first trimester also had the strongest associations, compared to higher fish intake during the second through fourth trimester
  • Above 600 grams of fish per week the cognitive benefits tapered off, suggesting this may be an ideal level, above which the risks of mercury exposure could begin to outweigh the benefits

I was not aware of these intriguing results but find it interesting in light of my transition to 4 ounces most days of either anchovies, sardines or Vital Choice Alaskan salmon. This is around 700 grams a week.

Additionally, many are concerned about Fukushima radiation contaminating fish. While I don't doubt it is an issue for some fish, I personally test the fish I consume from Vital Choice with a $1,000 Inspector Geiger counter and it has never measured anything higher than background radiation.

Recommendations for Pregnant Women

While fish have always been an ideal, rich source of omega-3 fat, the presence of pollutants such as PCBs and mercury does make caution advisable. It's not a reason to ditch ALL fish from your diet though.

As detailed in a presentation by a leading expert from Harvard Medical School,7 it's important to understand both the risks of consuming high-mercury fish and the benefits that low-mercury fish provide.

Your total mercury exposure depends on two factors: which fish you eat and the amount of fish you eat. The challenge is to select fish that qualify as low or very low in mercury.

Fortunately, the U.S. government has finally seen the light and is now specifying that pregnant women should be careful to select low-mercury seafood.

The joint recommendation8 by the U.S Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) regarding fish consumption for pregnant women, those who may become pregnant, breastfeeding mothers, and young children is 8 to 12 ounces of fish per week from choices that are lower in mercury.

In their estimation, this maximizes the benefits of omega-3 while minimizing the risk of mercury exposure. According to the study above, this may even be a conservative estimate.

Resources for Identifying Fish Low in Mercury

So where can you find information about the mercury content of any given fish species? Here are three resources:

  • The FDA has a Webpage9 listing and ranking seafood based on their mercury content
  • For a list that you can print out for reference, please see the Mercury Policy Project's guide to mercury levels in fish and shellfish10
  • The National Resources Defense Council has a mercury calculator you can use to give you an idea of how much mercury you're getting from any given fish species

Best and Worst Fish Choices

On the up-side, several fish species that are low in mercury are also high in omega-3s. Wild-caught Alaskan salmon11 is one example. Just one 3.5-ounce serving provides around 2 grams of omega-3s,12 which is more than most Americans ingest in a week. Only walnuts and flaxseeds provide more.13 Another benefit is that it has a nicely balanced omega-3 to omega-6 ratio.

Other species with lower mercury content include pollock, tilapia, catfish, and cod, along with smaller fish like sardines and anchovies. There are some questions as to the sustainability of anchovies though.

According to Wild Planet,14 anchovies are an abundant and prolific fish stock, and a fine sustainable choice, but the Safina Center's Sustainable Seafood Program15 and The Environmental Defense Fund16 give Mediterranean and Black Sea anchovies a poor eco rating.

Avoid tilefish, shark, swordfish, and king mackerel, as these four have the highest mercury levels of any fish tested. The FDA/EPA also wisely recommends limiting white albacore tuna to 6 ounces per week due to its elevated mercury content. Tuna is by far the largest source of mercury exposure in our diet —especially for children — and anyone who wants to reduce their mercury intake should eat less tuna.

According to a 2012 report17 by the Mercury Policy Project, young children should eat light tuna no more than twice a month, and albacore tuna should be avoided entirely. The report also recommends that if your child eats tuna once per week or more, you should have their blood tested for mercury. If the result is over 5 micrograms per liter (ug/L), his or her consumption should be restricted.

At What Level Does Mercury Become a Health Hazard?

Mercury is extremely toxic, so ideally, you don't want to be exposed to any. However, given the level of mercury pollution in the world today, this probably isn't feasible. You're bound to ingest or be exposed to some here and there, be it via air, water, of fish. Keep in mind that methylmercury harms a person's nervous system to differing degrees depending on how much mercury you've accumulated.

At above average doses, brain functions such as reaction time, judgment, and language can be impaired. At very high exposures, mercury can affect your ability to walk, speak, think, and see clearly.

One 2012 study18 that evaluated the effects of mercury on cognition in otherwise healthy adults found that those with blood mercury levels below 5 µg/L had the best cognitive functions. Mild impairment was evident at blood mercury levels of 5 to 15 µg/L and above 15 µg/L, cognition was significantly impaired.

When it comes to infants, studies have associated prenatal methylmercury exposure with impaired development of sensory, motor, and cognitive functions, resulting in learning difficulties, poor coordination, and inability to concentrate.

But bear in mind that the benefits of the omega-3 you get from fish can, and most likely does, outweigh the risk of methylmercury provided you don't overdo it, and stay away from fish known to be high in mercury. Again, the featured study found NO additional cognitive benefits for eating more than 600 grams/21 ounces of fish per week, which is about 4 servings.

A more cautious recommendation would be to limit your fish consumption to a maximum of 12 ounces of high omega-3/low-mercury varieties and take a high quality omega-3 supplement, such as krill.

If you believe your health problems may be related to mercury toxicity, get tested for heavy metals, and if need be, take appropriate action to detoxify. For more information, see my Revised Mercury Detox Protocol. That said, it's undoubtedly easier to avoid mercury exposure than it is to detoxify once it has built up. This is why it's so important to use discernment when selecting seafood.

Beware of Farmed Fish

While the FDA/EPA recommends salmon, they do not specify the type of salmon. I strongly discourage consumption of farmed salmon due to their inferior nutritional profile, their environmental drawbacks, and potential health hazards, detailed in my previous article, "Norway Issues Warnings About Health Dangers of Farmed Salmon."

Unfortunately, recent investigations19 have shown that as much as 80 percent of the fish marked as "wild" may actually be farmed, and that includes salmon. In restaurants, 90 to 95 percent of salmon is farmed, yet often listed on the menu as "wild."

Given these inaccuracies, how can you tell whether a salmon really is wild or farmed? The flesh of the salmon will give you a clue. Wild sockeye salmon is bright red, courtesy of its natural astaxanthin content. Sockeye salmon actually has one of the highest concentrations of natural astaxanthin of any food.

Wild salmon is also very lean, so the fat marks — those white stripes you see in the meat — are quite thin. If a fish is pale pink with wide fat marks, the salmon is likely farmed. Avoid Atlantic salmon, as salmon bearing this label are almost always farmed.

The two designations you want to look for are: "Alaskan salmon" (or wild Alaskan salmon) and "sockeye salmon," as neither is allowed to be farmed. Canned salmon labeled "Alaskan salmon" is a good bet, and if you find sockeye, it too is assured to be wild (provided it's not mislabeled; again be sure to visibly inspect the fish and look for the telltale signs).

My favorite brand of wild Alaskan salmon is Vital Choice Wild Seafood and Organics, which offers a nice variety of high-quality salmon products that test high for omega-3 fats and low for contaminants.

In addition to PCBs and mercury, radiation from the leaking Fukushima power plant in Japan is another concern, and many have simply given up on eating fish for fear of radioactive contamination, or they opt for farmed fish, thinking it's a safer option. I disagree on the latter point. Instead, I would suggest contacting the distributor of whatever wild fish you may be interested in, and ask them whether or not they test for radiation.

If You Choose Wisely, the Benefits of Fish May Still Outweigh Its Risks

As you can see, the situation is complex. You absolutely need omega-3 fats, as your body cannot make it, but it's not as easy as saying "eat more fish." You also need to take pollutants into account (including potentially radioactive contaminants).

This is particularly important for pregnant women and young children. Sustainability is yet another factor that is worthy of consideration. The good news is that even when all of these factors are taken into account, you have still have a number of good, viable options available.

To reiterate, wild-caught Alaskan (not Atlantic) salmon is very high in omega-3 and among the lowest in mercury. It's also still a sustainable choice, plus it's not allowed to be farmed — another benefit — and it has not been genetically engineered, so the likelihood of accidentally getting the now approved GMO salmon when buying wild Alaskan is limited. For other good options, see the three resources listed earlier.

Last but not least, even if you eat fish, you may benefit from taking a high-quality omega-3 supplement such as krill oil, which is a far more sustainable choice than fish oil. The best certification for sustainability my team has found is The Marine Stewardship Council.20 We spent quite a bit of time and expense working with them; it took over 5 years of observation, but they have certified our krill supply as one of the best managed resources in the world.21

If you avoid fish, an omega-3 supplement like krill oil becomes an absolute necessity. If you’re pregnant, I would highly recommend taking the “better safe than sorry” route, and limit fish to about 12 ounces per week, and supplement with krill oil, as there’s very little risk of krill being contaminated with heavy metals and other pollutants. 


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