A pregnant person can consume tuna, but this must be done with careful attention to the type of tuna and strict limits on the quantity eaten each week. This necessary moderation is directly related to the varying levels of a specific contaminant found in nearly all seafood. Consumers must make informed choices to balance nutritional benefits against potential risks.
Why Mercury is the Main Concern
The primary reason for limiting tuna consumption during pregnancy is the presence of methylmercury, a potent neurotoxin. Mercury exists in the environment and is converted by bacteria in aquatic systems into this organic form, which then accumulates in fish tissue. As larger, predatory fish consume smaller fish, the concentration of methylmercury increases up the food chain, a process called biomagnification.
When a pregnant person consumes fish containing methylmercury, the compound easily crosses the placenta and the fetal blood-brain barrier. The developing fetal nervous system is acutely sensitive to this substance, even at low levels of exposure. Limiting intake minimizes the risk of this neurotoxin interfering with the healthy formation of the baby’s brain and nervous system throughout gestation.
Distinguishing Safe Tuna Varieties
Not all canned tuna is the same when it comes to mercury content, and the distinction is paramount for safe consumption. Canned Light Tuna is the safer choice because it is typically made from smaller species, primarily skipjack tuna. These fish have shorter lifespans, meaning they accumulate significantly less methylmercury in their tissues compared to larger, older varieties. On average, canned light tuna contains about 0.12 parts per million (ppm) of mercury.
Canned White Tuna, or Albacore, poses a higher concern because it comes from a larger species of tuna that lives longer. The mercury concentration in albacore is often nearly three times higher than in light tuna, averaging around 0.35 ppm. This difference in mercury load is why health guidelines treat these two types of canned tuna very differently, making the label “chunk light” versus “albacore” a necessary check for pregnant consumers.
Official Weekly Consumption Guidelines
The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) offer specific advice to help pregnant individuals safely consume fish. They recommend consuming 8 to 12 ounces of low-mercury fish per week, which is equivalent to two to three average servings.
For Canned Light Tuna, which falls into the “best choices” category, pregnant people can safely eat two to three servings per week, totaling up to 12 ounces. However, for Canned White (Albacore) Tuna, the recommendation is much more restrictive due to its higher mercury content. The official advice is to limit the intake of canned albacore to no more than one serving, or 6 ounces, per week.
The Nutritional Value of Tuna
Beyond the focus on mercury, consuming tuna in the recommended amounts offers substantial nutritional benefits for both the pregnant person and the developing fetus. Tuna is a source of high-quality, lean protein, which is essential for all aspects of growth and development during pregnancy. It also provides important micronutrients like Vitamin B12, crucial for nerve function, and Vitamin D, which supports bone health and immunity.
The most significant benefit comes from the Omega-3 fatty acids, specifically docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). These long-chain polyunsaturated fatty acids are foundational for the healthy formation of the baby’s brain and visual system. Including low-mercury fish in the diet provides these components, which may also reduce the risk of certain pregnancy complications.