Why does the FDA recommend limiting the amount of fish in your diet? An explanation of mercury and other risks

October 19, 2025 •

4 min read

The FDA and EPA advise certain groups to limit their fish intake due to potential contaminants, primarily methylmercury. It is crucial for pregnant women, breastfeeding mothers, and young children, whose developing nervous systems are most vulnerable, to understand why does the FDA recommend limiting the amount of fish in your diet? while still enjoying its nutritional benefits.

Quick Summary

The FDA and EPA recommend limiting fish consumption for vulnerable groups like pregnant women and children mainly due to contaminants like methylmercury and PCBs, which bioaccumulate in higher-trophic-level fish.

Key Points

Methylmercury is the primary concern: The FDA recommends limiting fish primarily due to methylmercury, a neurotoxin that accumulates in fish and can harm developing nervous systems.
Vulnerable groups need extra caution: Pregnant women, breastfeeding mothers, and young children should adhere strictly to guidelines for safer, low-mercury fish.
Larger predatory fish have more mercury: Older, predatory species like shark and swordfish, which are higher on the food chain, contain the highest levels of mercury and should be avoided.
Lower-mercury options are abundant: Many commonly consumed fish like salmon, shrimp, and tilapia are considered "Best Choices" by the FDA and can be eaten in moderation.
Benefits outweigh risks for safe choices: The omega-3 fatty acids and other nutrients in low-mercury fish are important for brain development and heart health, and the FDA's advice helps maximize benefits while minimizing risks.
Check local advisories: For fish caught recreationally, always check for local and state advisories, as contamination can vary by waterway.

The Primary Concern: Methylmercury Contamination

Mercury is a naturally occurring element found in rocks, soil, and coal. However, industrial activities, such as burning fossil fuels and mining, have significantly increased its presence in the environment. In aquatic ecosystems, bacteria convert this mercury into a more toxic form called methylmercury. This potent neurotoxin then accumulates in fish, a process known as bioaccumulation. As smaller, mercury-contaminated fish are consumed by larger predators, the concentration of methylmercury increases at each step up the food chain, a process called biomagnification. This is why larger, longer-lived predatory fish tend to have the highest mercury levels. The FDA and EPA’s advice is primarily a public health strategy to help consumers navigate this risk by providing guidance on how to make safe choices.

The Risks for Vulnerable Populations

Certain populations are more susceptible to the harmful effects of methylmercury exposure. The FDA’s advice is particularly focused on protecting the health of these vulnerable groups.

Pregnant and Breastfeeding Women: For these groups, high mercury exposure poses a risk to the developing nervous system of the fetus or infant. The methylmercury can cross the placenta and enter breast milk, potentially impacting the child's brain development and cognitive function.
Young Children: Similar to infants, children's developing brains and nervous systems are more vulnerable to the effects of mercury. The FDA provides specific portion size recommendations for children based on age and body weight to minimize exposure.

For adults, the risks of adverse short-term health effects from typical seafood consumption are generally low. However, high levels of exposure over time can lead to neurological issues and other health problems.

Other Contaminants Found in Fish

Beyond mercury, fish can contain other persistent organic pollutants (POPs) that pose health risks, particularly in fish from polluted waterways.

Polychlorinated Biphenyls (PCBs): These industrial chemicals were banned decades ago but persist in the environment and accumulate in the fatty tissues of fish. PCBs have been linked to cancer, reproductive issues, and immune system dysfunction.
Dioxins and Pesticides: Dioxins are toxic byproducts of industrial processes, while pesticides can enter waterways through agricultural runoff. These substances also accumulate in fish tissue.

Removing the skin and fatty portions of fish before cooking can help reduce the intake of some of these fat-soluble contaminants, but it does not remove mercury, which is bound to the protein in the fish meat.

Balancing Risks and Benefits

Despite the concerns, fish is a vital part of a healthy diet, providing high-quality protein, essential omega-3 and omega-6 fatty acids (like DHA and EPA), and important vitamins and minerals. Omega-3s are especially beneficial for heart health and brain function. The FDA's advice is not to avoid fish but to make strategic, safe choices. Most Americans consume less fish than the recommended amount, so making wise selections is key.

How to Choose Safer Fish: The FDA's Guide

To help consumers, the FDA and EPA created a tiered system for choosing fish based on mercury levels.

Best Choices (Eat 2 to 3 servings a week)

Salmon
Shrimp
Canned Light Tuna (Skipjack)
Tilapia
Cod
Catfish
Pollock
Sardines
Freshwater Trout
Flounder

Good Choices (Eat 1 serving a week)

Halibut
Mahi Mahi
Grouper
Snapper
Canned White (Albacore) Tuna
Bluefish
Tuna (Yellowfin)

Choices to Avoid (Highest Mercury Levels)

King Mackerel
Marlin
Orange Roughy
Shark
Swordfish
Tilefish (Gulf of Mexico)
Tuna (Bigeye)

Local Catch Advisories

When eating fish caught recreationally from local waters, it is essential to check for specific local advisories from state or tribal health and environmental agencies. These advisories account for specific local pollution that may not be reflected in general commercial recommendations. If no advisory is available, the FDA suggests limiting consumption of that fish to one serving per week and eating no other fish that week.

Comparison of High vs. Low-Mercury Fish

To illustrate the difference in FDA recommendations, consider the following comparison table:


Feature	High-Mercury Fish (Choices to Avoid)	Low-Mercury Fish (Best Choices)
Examples	Shark, swordfish, king mackerel, marlin, bigeye tuna, Gulf of Mexico tilefish	Salmon, shrimp, tilapia, cod, catfish, canned light tuna
Mercury Level	Highest; accumulates due to lifespan and diet	Lowest; shorter lifespans and lower trophic levels
Dietary Recommendation	Avoid, especially for pregnant women and children; other adults should limit to no more than 1 serving/week	Recommended 2–3 servings per week for most adults and vulnerable groups
Predatory Role	Apex predators; consume other fish	Often lower on the food chain; primarily consume plankton or smaller prey
Risks	Higher risk of neurotoxicity due to mercury	Lower risk of mercury exposure, higher omega-3 benefits

Conclusion

The FDA's recommendation to limit the amount of fish in your diet is a responsible public health measure aimed at minimizing exposure to contaminants, particularly methylmercury. This advice is especially critical for vulnerable populations like pregnant women, breastfeeding mothers, and young children, where the risks to a developing nervous system are greatest. By focusing on a variety of low-mercury options and staying informed about both commercial and local fish advisories, you can continue to enjoy the significant nutritional benefits of fish while making safe and healthy dietary choices. For more detailed information, consult the official FDA guidelines.

The Role of Omega-3s and Other Nutrients

It's important to remember the nutritional upside of fish. It's a key source of omega-3 fatty acids, which are essential for brain development in infants and heart health in adults. Many low-mercury fish, such as salmon and sardines, are excellent sources of these fats. Fish also provides high-quality protein, Vitamin D, iodine, and zinc, all of which contribute to overall health. The goal of the FDA's guidance is not to create fear of fish, but to provide a framework for balancing these benefits with the potential risks of contaminants.

Frequently Asked Questions

Mercury is a potent neurotoxin that can cross the placenta and impact a developing baby's brain and nervous system. Children are also more susceptible due to their smaller size and ongoing brain development, which can be affected by even low levels of exposure.

The FDA lists salmon, shrimp, canned light tuna (skipjack), tilapia, cod, and catfish among the best, low-mercury options.

Mercury is released into the environment from natural sources and human activities like fossil fuel burning. It settles in water, where bacteria convert it to methylmercury, which is then absorbed by aquatic organisms and accumulates up the food chain.

No, cooking methods like baking, frying, or grilling do not remove mercury from fish. The mercury is bound to the protein in the fish's meat and remains after cooking.

No, canned light tuna typically has less mercury than canned albacore ("white") tuna because albacore are larger and live longer. The FDA recommends limiting canned albacore tuna to one serving per week.

While mercury is the most common concern, other contaminants like PCBs, dioxins, and pesticides can be present, especially in fatty fish from contaminated waters. Removing skin and fat can help reduce exposure to some of these pollutants.

You should check advisories issued by your state or local health department or fish and game agency for guidance on consuming locally caught fish. This is important because contamination can vary significantly by waterway.

No. The FDA emphasizes eating a variety of fish over time. If you miss a week, you can resume your regular consumption the following week without trying to catch up.