I rarely write website articles on prenatal issues, but I thought that the fish debate was one that would be interesting, not just to my patients who are considering getting or are already pregnant, but also to their mothers, mother-in-laws and the rest of the family and friends who eagerly offer advice as soon as they see them picking up a fork. A recent article in the American Journal of Obstetrics and Gynecology reviewed the updated advice by the FDA for pregnant and breast-feeding women.Their underlying message seem to be that, rather than avoiding fish consumption during pregnancy and breast-feeding, women should eat fish with high levels of omega 3 fatty acid (EPA and DHA ) and low levels of mercury. They stated that maternal ingestion of adequate quantities of fish (defined as at least 350 g of oily fish each week) has been associated with better childhood IQ scores, fine motor coordination, communication and social skills, and a reduced incidence of postpartum depression.
The problem is that the FDA did not specify how much omega-3 fatty acid should be ingested each day or state which fish would safely provide that amount; it did however specify which fish to avoid because of high mercury levels. The Environmental Protection Agency has determined that the safe allowable methyl mercury intake during pregnancy is roughly 42 to 64 µg per week. Based on this the FDA advised against eating shark, tilefish, swordfish and king mackerel during pregnancy or while breast-feeding because they have the highest mercury levels (100 – 220 micrograms per 4 ounce serving). The FDA has also recommended limiting consumption of albacore tuna to 6 ounces per week, although other kinds of tuna (bluefin, skipjack and yellowfin) and lobster apparently also have fairly high levels of mercury.
And we’re kind of screwed when we looked at the difference between farm fish and wild caught fish; the former contain higher levels of PCBs and dioxin, the latter may have high levels of mercury. Fatty sport fish from PCB contaminated lakes such as the Great Lakes may have really high levels. Just to make you more fish conscious, PCB exposure has been associated with lower IQ scores, greater impulsivity and poor concentration and memory in exposed children. And what about good old shrimp? It is the most commonly consumed seafood in the United States and usually contains no mercury so it might be considered ideal. But it fails as a great source of omega 3 fatty acid… a 4 ounce serving contains only 100 µg of DHA and EPA.
So why not just take this important fatty acid as a supplement? Well… the FDA has stated that “the entire package of nutrients that fish provide may be needed to fully benefit fetal and child development” and that women who avoid fish and instead take omega-3 fatty acid supplements may have missed out on many of the benefits for overall health for their children as well as themselves. Randomized trials of antenatal or prenatal omega 3 fatty acid or fish oil supplements have found no sustained improvement in cognitive, language or motor scores in children who are exposed as fetuses and there was no benefit for cardiovascular health or postpartum depression for the mothers. It may be that the DHA and EPA found in dietary supplements don’t have the same metabolic properties as those occurring naturally in fish. Moreover, we don’t really know what the ideal dose of DHA or EPA should be. Last April the FDA published a rule prohibiting manufactures from stating that their products are “high” or “rich” in or an “excellent source” of DHA and or EPA.
Bottom line: Pregnant and nursing women should eat fish because fish contains omega 3 fatty acid essential for fetal brain development and because it does not appear that dietary supplements have the same beneficial effects. The best fish are probably salmon, pollack and squid as well as Atlantic cod. The somewhat good news is that pollack is the main fish used for fast food fish sandwiches…so you can get it at all those places we usually tell you to stay away from… Just decline the fries!)