July 2011 Issue

Shifting Tide — Experts Reassess Risks of Eating Fish During Pregnancy
By Christin L. Seher, MS, RD, LD
Today’s Dietitian
Vol. 13 No. 7 P. 22

Open almost any pregnancy book on the shelf these days and you will find an entire chapter or more devoted to discussing what women should eat when they are expecting. As a new mother myself, I would know.

While the specifics may change from author to author, the messages are usually the same: Pregnant women should choose a variety of healthful foods to meet their increased nutrient needs; aim for steady, healthy weight gain within recommended ranges; and save a little room to indulge in those unique pregnancy cravings. Additionally, pregnant women are encouraged to keep their fish and seafood intake low due to worries over toxins (eg, mercury) that might be dangerous to the baby. When it comes to this latter recommendation, though, these books may be due for an update.

Guidelines Get New Bearings
Since 1994, when growing concern over the mercury content of fish caused the FDA to issue its first cautionary statement to women who were pregnant or were thinking about becoming pregnant, messages surrounding fish consumption have been cause for controversy.1 Historically, agencies such as the FDA, the Environmental Protection Agency, and the American Dietetic Association (ADA) have recommended that pregnant women limit their fish consumption to no more than 12 oz per week of varieties low in mercury due to concerns over potential hazards to the developing fetus.2,3 Research demonstrates that because of these advisories, women have decreased their intake of fish and seafood (or choose to forgo it altogether) while pregnant because of concerns about potential contaminants and the effect on their unborn children.4,5

But the 2010 Dietary Guidelines for Americans, the first set of national guidelines to be based on a detailed review of evidence, now recommend that pregnant and breast-feeding women include 8 to 12 oz of fish and seafood low in mercury as part of a healthful diet.

As in years past, the 2010 Dietary Guidelines emphasize that Americans should make healthful food selections that are nutrient dense, noting “a healthy eating pattern limits intake of sodium, solid fats, added sugars, and refined grains and emphasizes nutrient-dense foods and beverages,” including seafood. In addition, the Dietary Guidelines still promote an overall reduction of foods high in saturated fats and cholesterol.2

But new to the 2010 version is the specific recommendation to “increase the amount and variety of seafood consumed by choosing seafood in place of some meat and poultry.”2 While this recommendation applies to all Americans, the Dietary Guidelines go one step further, advising women who are pregnant or breast-feeding to consume 8 to 12 oz of seafood per week from a variety of seafood sources, though noting that they should avoid certain types of fish (eg, swordfish, king mackerel) due to their high mercury content.2

Sea of Potential Benefits
Perhaps the primary reason to include fish and seafood products in the diet during pregnancy is that they are nutritional powerhouses. “Ounce for ounce, fish is generally lower in calories than other meats and contains higher concentrations of ‘healthy’ fats,” notes Judith Brown, PhD, author of several books on nutrition, including Nutrition Through the Life Cycle and What to Eat Before, During, and After Pregnancy. “Like other meats, fish are a good source of high-quality protein and a variety of minerals.” These properties make fish an excellent choice for pregnant women looking to keep weight gain within a healthy range while simultaneously meeting the body’s increased nutrient demands.

More importantly, fish and seafood are the most plentiful dietary sources of healthful long-chain omega-3 polyunsaturated fatty acids (PUFAs), such as EPA and DHA.6 One of the main benefits of fatty fish consumption is that it supplies the DHA needed for a baby’s brain development, says Melinda Johnson, MS, RD, media spokesperson for the ADA and a lecturer at Arizona State University. She notes that babies need enough DHA for proper nervous system and eye development. “It is very difficult to find DHA in other food sources besides fatty fish,” she explains.

On the basis of past advisories, physicians and pregnancy books have historically instructed pregnant women to be extremely cautious regarding their fish consumption due to methylmercury content. According to the FDA, “The effect of methylmercury on infants may be as subtle as delayed development or as severe as mental retardation. Because women may not display any symptoms of toxicity when their blood level of methylmercury is sufficiently high to cause fetal damage, prevention of exposure to unsafe levels of methylmercury is crucial.”1

A plethora of recent research, however, highlights the health benefits of consuming DHA, especially during pregnancy. As fish and seafood remain one of the best dietary sources, it is therefore more important than ever to educate women on the type and amount of fish and seafood that is safe for consumption during this time.

“Safe fish and seafood for pregnant women are those that are high in EPA and DHA and low in mercury content. Fish such as shad, salmon, anchovies, herring, whitefish, mackerel, sardines, and flounder qualify as ‘safe.’ Shrimp, clams, and canned light tuna are also relatively good sources of EPA and DHA and are low in mercury content. Swordfish, king mackerel, tilefish, and shark tend to contain high amounts of mercury and should not be consumed by pregnant women,” says Brown.

One proposed benefit of fish consumption is a reduction in depressive symptoms. While some studies have revealed conflicting results, most (across case-control, cohort, double-blind randomized control trials, population-level, and individual studies) support an association between increased omega-3 polyunsaturated fatty acid intake (DHA and EPA found in fish and fish oils) and a reduction in depressive symptoms in the overall population.6,7 Due to the needs of the developing fetus, researchers believe that DHA and EPA levels in pregnant women may be reduced, thereby increasing their risk of depression if their circulating levels are not augmented through higher dietary intake or supplementation.7

Research in this area, however, is inconclusive. One study examining this relationship surveyed almost 2,400 pregnant women regarding their fish consumption and depressive symptoms. The researchers found no overall association between fish consumption and depressive symptoms during pregnancy, although they did see an association for specific subgroups of their study population (specifically smokers and single mothers).7

The relationship between omega-3 intake and postpartum depression also remains murky. Several cohort studies report decreased levels of omega-3 PUFA in women with postpartum depression compared with nondepressed women.6 Yet a 2010 meta-analysis of the few randomized controlled trials that exist demonstrates no significant difference in depressive symptoms when women are given omega-3 supplementation vs. placebo postpartum.8

Another reported benefit of fish and fish oil consumption during pregnancy is the potential protective effect mediated by the omega-3 fatty acids found in fish. As precursors to prostaglandins, these PUFAs have a hypotensive effect that may help reduce the risk of preeclampsia and preterm birth.3 Additionally, the consumption of DHA and EPA has been associated with longer gestational length and higher birth weight.9

According to Guesnet and Alessandri, authors of a recent mini review, another reason to consume omega-3s (specifically DHA) during the prenatal period is that maternal intake is crucial in determining postnatal DHA levels in infants. As DHA is critical for early brain and visual development, the consumption of DHA during gestation has the potential to augment an infant’s neurodevelopment. Research is ongoing, however, as this topic has not been extensively studied and results to date are inconclusive. But there is promising evidence to suggest that maternal DHA consumption can have beneficial impacts on children’s visual acuity and problem-solving abilities.10

Some Cautions
Besides mercury, Johnson notes that fish can contain other pollutants, such as polychlorinated biphenyls (PCBs), dioxins, or DDT, which may be cause for concern—another reason to know the source of any fish consumed during pregnancy. But, according to Brown, “A number of studies have examined fish content of substances such as cadmium, lead, arsenic, PCBs, and other chlorinated pesticides. Concentrations of these substances have been found to be well below established maximum intake levels. Of the possible contaminants, mercury appears to stand out as the substance in fish to generally avoid.”

In addition to contaminants in fish and seafood products, pregnant women also need to be cautious of food-borne illnesses when including these foods in their diet. According to Sandra Hudak, PhD, RD, LD, an associate professor of nutrition/dietetics at the University of Akron in Ohio, “Although recent research [published in Canadian Family Physician in April 2010] has indicated that pregnant women no longer have to avoid foods like raw or undercooked seafood, the FDA advises pregnant women to cook all fish and seafood prior to consumption. Food-borne illness from raw seafood includes contamination from Salmonella, Staphylococcus aureus, and viral infections. In addition to the risk of food-borne illness, raw fish may contain parasites.”

Advice From the Experts
According to the experts interviewed for this article, the nutritional benefits of consuming fish during pregnancy outweigh the risks as long as women are smart about the type and quantity of fish consumed. Both the FDA and ADA advise that in addition to avoiding species of fish that are traditionally higher in mercury content, pregnant women should exercise caution in consuming fresh, local fish. The FDA states, “Before eating fish caught by family or friends, individuals should determine what body of water the fish came from and check with state agencies to make sure that body of water has not been found to have dangerously high levels of mercury.”

The FDA and ADA note that if local advisories determining the safety of fish in nearby lakes, rivers, and coastal areas are unavailable, then consuming up to 6 oz of fish per week from local waters (and no other fish) is considered safe for pregnant and breast-feeding women.

Pregnant women must also handle fish and seafood properly to minimize the risk of food-borne illness. Until research conclusively demonstrates that raw or uncooked seafood consumption is safe and national guidelines are updated, women should still be cautious, following safe food-handling practices for fish and seafood.

According to Hudak, many of the contaminants in fish, such as Salmonella and parasites, can be destroyed when fish is cooked to 145˚F. Freezing at -10˚F for seven days will kill parasites. “Fish should always be selected from a reputable market, then stored and cooked to the appropriate internal temperature,” she says. “Because pregnant women are part of a vulnerable population, all precautions should be taken to prevent food-borne illness, which includes consuming only properly cooked fish and seafood.”

Still a Bit Seasick?
If women have lingering concerns about including fish and seafood in their diet during pregnancy, they can reap the health benefits of omega-3 fats in other ways. “Women can still consume the recommended 200 to 300 mg of DHA plus EPA daily by taking a third to a half teaspoon per day of fish oil or an algae oil supplement,” advises Brown. However, while these oils are often rich in DHA and EPA, they provide limited nutritional benefit beyond being a concentrated source of healthy fats, notes Brown, adding that women should be cautious of fish liver oils because they may contain excessively high amounts of the fat-soluble vitamins A and D.

Alternatively, as Johnson points out, pregnant women can “eat other food sources of omega-3 fatty acids, because your body can turn a small part of these fatty acids into DHA. These food sources include ground flaxseed and walnuts.” But the body is inefficient at this conversion, so consuming DHA and EPA directly is the most effective way to obtain their important health benefits. Johnson says women can look for fortified foods containing DHA, such as milk or eggs, or take a fish oil pill.

Other food products are fortified as well, notes Brown. “Some margarines and beverages are fortified, but you have to check the product’s label to make sure the omega-3s added to the products are DHA and EPA and not alpha-linolenic acid,” she warns.

But, Brown continues, “Many people who don’t care much for fish are trying to eat more of it. Women who belong to this group can Google the search term ‘fish dishes for people who don’t like fish’ and find a bunch of recipes that promise to take the fishiness out of fish dishes. You can also add a third to a half teaspoon of fish oil to oil-based salad dressings and put that on your salads to boost your DHA and EPA intake.”

This extra effort just may be a way to reel in some promising health benefits.

— Christin L. Seher, MS, RD, LD, is founder of Strategic Health Solutions, LLC, serving northeastern Ohio.


Advice in a Handy Guide
The National Resources Defense Council has created a wallet guide containing a list of fish and their mercury levels so pregnant women can be informed about what they are consuming. Download it for free at www.nrdc.org/health/effects/mercury/walletcard.pdf.


1. Evans EC. The FDA recommendations on fish intake during pregnancy. J Obstet Gynecol Neonatal Nurs. 2002;31(6):715-720.

2. U.S. Department of Agriculture, U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th ed. Washington, D.C.: U.S. Government Printing Office; 2010. Available at: http://www.cnpp.usda.gov/publications/dietaryguidelines/2010/policydoc/execsumm.pdf. Accessed April 26, 2011.

3. Kaiser L, Allen LH; American Dietetic Association. Position of the American Dietetic Association: Nutrition and lifestyle for a healthy pregnancy outcome. J Am Diet Assoc. 2008;108(3):553-561.

4. Oken E, Kleinman KP, Berland WE, Simon SR, Rich-Edwards JW, Gillman MW. Decline in fish consumption among pregnant women after a national mercury advisory. Obstet Gynecol. 2003;102(2):346-351.

5. Coletta JM, Bell SJ, Roman AS. Omega-3 fatty acids and pregnancy. Rev Obstet Gynecol. 2010;3(4):163-171.

6. Sontrop J, Campbell MK. Omega-3 polyunsaturated fatty acids and depression: A review of the evidence and a methodological critique. Prev Med. 2006;42(1):4-13.

7. Sontrop J, Avison WR, Evers SE, Speechley KN, Campbell MK. Depressive symptoms during pregnancy in relation to fish consumption and intake of n-3 polyunsaturated fatty acids. Paediatr Perinat Epidemiol. 2008;22(4):389-399.

8. Jans LA, Giltay EJ, Van der Does AJ. The efficacy of n-3 fatty acids DHA and EPA (fish oil) for perinatal depression. Br J Nutr. 2010;104(11):1577-1585.

9. Greenberg JA, Bell SJ, Ausdel WV. Omega-3 fatty acid supplementation during pregnancy. Rev Obstet Gynecol. 2008;1(4):162-169.

10. Guesnet P, Alessandri JM. Docosahexaenoic acid (DHA) and the developing central nervous system (CNS) — Implications for dietary recommendations. Biochimie. 2011;93(1):7-12.