Tuna tartare, a dish composed of raw, finely diced tuna often blended with an acidic or savory dressing, presents a complex health decision for individuals who are pregnant. The appeal of the dish clashes with two distinct and significant health concerns that arise during gestation. The primary issue is the inherent danger of consuming any uncooked fish, which carries an immediate risk of foodborne illness. This is compounded by a second, long-term concern specific to tuna: the potential exposure to a neurotoxic heavy metal that accumulates in the fish’s tissue. Understanding these dual risks is necessary for making an informed choice.
Pathogen Risks of Consuming Raw Fish
The consumption of any raw or undercooked fish, including tuna tartare, poses an immediate threat of foodborne illness, which is amplified during pregnancy. Pregnant people are physiologically more susceptible to infections like listeriosis, an illness caused by the bacterium Listeria monocytogenes. Changes in the immune system during gestation make it easier for the bacterium to establish an infection.
While listeriosis often causes only mild, flu-like symptoms in the mother, the consequences for the developing fetus can be severe. The infection can cross the placenta, leading to outcomes such as miscarriage, stillbirth, preterm delivery, or life-threatening infection of the newborn. Heat is the only reliable method to eliminate this bacterial risk.
Raw fish also carries a risk of parasitic contamination, most notably from larval worms like Anisakis species. Ingesting these parasites can cause anisakiasis, a condition characterized by severe abdominal symptoms. While commercial freezing practices are mandated for most fish intended for raw consumption in the United States to kill these parasites, the preparation method itself removes the safety step of cooking.
The inherent lack of heat treatment in tartare means that any lapse in handling, freezing, or preparation can allow pathogens to survive. The finely diced nature of the tartare increases the surface area exposed to potential contamination. For these reasons, health organizations generally advise against consuming any raw or undercooked seafood during pregnancy.
Fetal Development and Mercury Exposure
Shifting from the risk of microbial contamination, the specific composition of tuna introduces the long-term risk of heavy metal exposure, independent of the cooking method. Tuna are large, long-lived predatory fish, which means they are high on the aquatic food chain. This position causes them to accumulate methylmercury, a potent neurotoxin, through a process called biomagnification.
Methylmercury is the form of mercury that is most easily absorbed and is found in high concentrations in tuna tissue. Once ingested by the mother, this compound can readily cross the placenta. In fact, the concentration of methylmercury in a newborn’s blood can sometimes exceed that of the mother’s, suggesting the placenta actively transfers the substance to the fetal circulation.
The fetal nervous system is particularly vulnerable to methylmercury exposure, especially during the second half of gestation when brain cell migration is in full swing. The toxin can interfere with the movement of developing brain cells and halt cell division, impairing the formation of the brain. High levels of exposure have been linked to deficits in memory, learning, attention span, and coordination that persist into childhood.
The type of tuna used in tartare is a determining factor for the mercury level, as the dish often uses species like Bigeye or Ahi tuna, which are known to have high methylmercury content. This contrasts with lower-mercury options, such as canned light or skipjack tuna. Consequently, even a small, single serving of tartare made from a high-mercury species can contribute significantly to the mother’s body burden of the toxin.
Official Guidance and Safer Alternatives
Official health advice from organizations like the U.S. Food and Drug Administration (FDA) and the American College of Obstetricians and Gynecologists (ACOG) is clear regarding the dual concerns of tuna tartare. Due to the risk of listeriosis and other foodborne illnesses, pregnant individuals are strongly advised to avoid all raw and undercooked seafood. The lack of a heat-based kill step makes any raw preparation unsafe.
Regarding the mercury risk, these organizations recommend that pregnant people avoid fish that are known to have the highest concentrations of methylmercury. While fish provides beneficial nutrients like Omega-3 fatty acids, the potential for neurological harm from high-mercury species outweighs the benefit. Therefore, tuna tartare is generally considered unsafe on two fronts: the risk from raw preparation and the high mercury content of the tuna species commonly used.
Pregnant individuals are encouraged to consume 8 to 12 ounces of a variety of fish that are lower in mercury per week, which amounts to two or three servings. Safer options to satisfy a seafood craving include fully cooked low-mercury fish:
- Salmon
- Cod
- Shrimp
- Tilapia
If a person still desires tuna, canned light or skipjack tuna is a better choice, but consumption of even this lower-mercury variety should be limited to moderate amounts per week.