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Pregnant? Eat Fish!

Research now suggests that the benefit to a baby's neurological health from omega-3s appears tothe potential for harm from small amounts of mercury in fish tissues
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For the last several years, many pregnant women have been seriously limiting -- or scrupulously avoiding -- fish in their diets. This is largely due to a 2004 advisory from the Food and Drug Administration and the Environmental Protection Agency recommending that pregnant women limit fish consumption to 12 ounces -- roughly two average meals -- per week, and that they eat varieties of fish and shellfish that are low in mercury (here's the whole advisory).

Unfortunately, the nuances of this recommendation were lost as it filtered into popular knowledge. What many women heard were the terms "mercury" "risk" and "harm" and on this basis ate much less fish than the advisory permitted - or none at all. A 2007 study showed that awareness of this warning drove 56 percent of pregnant women to needlessly reduce their fish consumption.

The problem with eating less fish during pregnancy is that it potentially deprives the developing fetus of vital nutrients. The omega-3 fatty acids, which are present in nearly all fish and particularly abundant in cold water varieties such as wild salmon, sardines, herring and black cod, are essential for healthy development of a baby's brain and nervous system. No other common food source delivers these nutrients in such quantity.

The crucial point: Research now suggests that the benefit to a baby's neurological health from omega-3s appears to far outweigh the potential for harm from small amounts of mercury in fish tissues.

A study from The Lancet published February 17, 2007, compared the children of three groups of women -- those who, during pregnancy, ate:

  • no fish
  • up to 12 ounces per week
  • more than 12 ounces per week

The research team was headed by Joseph R. Hibbeln, M.D., active chief of the Section of Nutritional Neurosciences at the National Institute on Alcohol Abuse and Alcoholism. He is perhaps the world's leading authority on the relationship between fat consumption and mental health. Dr. Hibbeln found that the children whose mothers avoided fish had almost double the risk of a low IQ by age 8. This was measured carefully in tests designed to isolate the effects of the amount of fish in the mothers' diets, and to exclude factors such as economic status or educational levels. Importantly, the children who did the best in the IQ testing were those whose mothers ate more than 12 ounces of fish per week while pregnant -- in other words, they exceeded the levels in the 2004 advisory.

What about mercury? Dr. Hibbeln's research indicates that the effect of ingested mercury by pregnant women from all sources -- not just fish -- in the U.S. appears to result in a lowering of the child's IQ by an average of less than one point. Meanwhile the effect of omega-3 deficiency as a result of avoiding fish is far more dramatic: a drop of five or six IQ points.

Based on such research, Jacquelyn Paykel, M.D., an obstetrician/gynecologist and integrative medicine specialist at the Medical College of Wisconsin, told me that she advises her pregnant patients to consume at least 12 ounces of seafood per week. She noted that the benefits of DHA (docosahexaenoic acid, one of the components of omega-3 fatty acids) include improvements in visual, cognitive, motor and behavioral skills in newborns that appear to correlate with improved lifelong health and mental capacity. She tells her patients that ocean fish, including salmon, chunk-light tuna, sardines and mackerel meet the need for DHA and EPA (eicosapentaenoic acid, also found in omega-3s) in pregnancy.

I concur with Dr. Paykel - pregnant women should consume at least 12 ounces per week of low-mercury fish. I suggest avoiding swordfish, marlin, shark and bluefish because they're more likely than other species to contain dangerous levels of toxins including mercury, and I recommend albacore over other species of tuna. Smaller fish are safer than larger ones. (Note: adequate dietary selenium protects tissues from harmful effects of mercury. I recommend taking 200 micrograms of selenium a day in supplement form.)

I am fully aware of two other often-cited hazards of eating fish. First, oil pollution from recent spills in the Gulf of Mexico and released radioactive particles from Japan's Fukushima Daiichi nuclear plant have raised concerns about seafood contamination. While both pollution sources bear watching, at this writing neither appears to seriously threaten the safety of commercially available fish. Second, while many worry that overfishing has depleted much of the world's fish stock, "fish stocks worldwide appear to be stable, and in the United States they are rebuilding, in many cases at a rapid rate," according to a recent New York Times Op-Ed piece by Ray Hilborn, a professor of aquatic and fishery sciences at the University of Washington. Even if this were untrue and fish were scarce, pregnant women would still be the most deserving recipients of this dwindling resource -- and should be absolutely the last group to have to give up fish.

Probably the lowest impact fish a pregnant woman -- or anyone else -- can consume is sardines. While overfishing has decimated predator fish, research indicates small forage fish such as sardines have doubled in population in the last 120 years.

Popular vegetarian omega-3 "substitutes" such as flaxseeds or walnuts are not nearly as beneficial. An omega-3 precursor, alpha-linolenic acid (ALA), occurs in these foods, but the body must convert ALA into EPA and DHA, an inefficient process that makes getting sufficient omega-3s from these sources very difficult. Grass-fed, grass-finished beef provides omega-3 fats, but again, fish are a far richer source, making these fats easier to obtain from fish in the context of an average diet.

The fact is that the human brain, by dry weight, is 60 percent fat. Human beings require abundant dietary omega-3 fatty acids to support the large brains and sophisticated nervous systems that set us apart from the other primates. Indeed, some anthropologists believe the human species diverged primarily because our early ancestors began to eat fat-rich fish, while our fellow simians remained content with low-fat leaves, roots and insects.

Fish, then, may have made us human -- and we need them today, particularly early in life, to reach our full potential. Consuming more fish would improve the health of Americans generally, and this is particular true for the developing fetus. If you are pregnant, eat fish!

Andrew Weil, M.D., invites you to join the conversation: become a fan on Facebook, follow him on Twitter, and check out his Daily Health Tips Blog. Dr. Weil is the founder and director of the Arizona Center for Integrative Medicine and the editorial director of

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