Pregnant individuals can safely enjoy a tuna sandwich, but safety depends on the type and quantity of tuna consumed. Fish is a recommended component of the prenatal diet, offering nutrients that support maternal health and fetal development. These benefits include high-quality protein and Omega-3 fatty acids, such as Docosahexaenoic Acid (DHA) and Eicosapentaenoic Acid (EPA), which are essential for the baby’s brain and eye function. However, some tuna contains a contaminant that requires careful monitoring during pregnancy.
The Primary Concern: Mercury and Fetal Development
The substance of concern in tuna and other seafood is methylmercury, a potent neurotoxin. Mercury released into the environment is converted by bacteria into this organic form, which accumulates in fish through bioaccumulation. Methylmercury passes easily across the placenta and concentrates in the developing fetus. The fetal nervous system is sensitive to this compound, especially during periods of rapid brain development. High prenatal exposure can lead to severe neurological issues, while chronic exposure is associated with subtle deficits in attention, cognition, and memory. Consumption guidelines balance the nutritional benefit of Omega-3s with the need to limit methylmercury exposure.
Practical Guidelines: Light Tuna vs. Albacore
The safety of a tuna sandwich depends on the species used. Canned tuna is categorized into two main types: “light” tuna and “albacore” tuna, also known as “white” tuna. Canned light tuna is typically skipjack, a smaller, shorter-lived species. These fish are lower on the food chain and accumulate less methylmercury. Albacore tuna, in contrast, comes from a larger, longer-living species. Because these fish live longer and consume more prey, they accumulate significantly higher concentrations of mercury. Canned albacore tuna contains approximately three times the mercury level found in canned light tuna. The difference in the size and lifespan of the fish is the biological basis for the differing consumption recommendations.
Determining Safe Weekly Servings
Regulatory bodies, including the U.S. Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA), provide guidelines based on the mercury content of different fish species. A single serving is defined as approximately 4 ounces, which is roughly the size of a pregnant individual’s palm. Canned light tuna is classified as a “Best Choice” due to its low mercury content. It can be consumed two to three times per week, translating to 8 to 12 ounces weekly. Albacore tuna, having higher mercury levels, is categorized as a “Good Choice.” The limit for albacore is stricter, permitting only one 4-ounce serving per week. These weekly limits are cumulative and must account for all fish consumed to ensure total methylmercury exposure remains safe.
Extending the Diet: Other Fish Choices
Beyond tuna, pregnant individuals are encouraged to eat 8 to 12 ounces of a variety of fish each week from the “Best Choices” category. This group includes many popular and highly nutritious options that are low in mercury. These alternatives provide high levels of Omega-3 fatty acids.
Best Choices
- Salmon
- Sardines
- Pollock
- Cod
- Tilapia
Conversely, a separate category of fish should be avoided entirely due to consistently high mercury concentration. These “Choices to Avoid” include large, predatory fish that have the longest lifespans, resulting in the highest degree of methylmercury bioaccumulation. Avoiding these specific species eliminates the highest-risk sources of mercury from the prenatal diet.
Choices to Avoid
- Shark
- Swordfish
- King mackerel
- Bigeye tuna
- Tilefish from the Gulf of Mexico