What are the downsides of canned fish?

December 25, 2025 •

5 min read

Americans consume over 1 billion pounds of canned tuna and pouches annually, a testament to its convenience, but this popularity doesn't erase the potential downsides of canned fish. While praised for protein and omega-3s, canned varieties can harbor contaminants and come with processing-related drawbacks that are crucial for consumers to understand.

Quick Summary

Canned fish, though a convenient protein source, may present health concerns including potential heavy metal contamination, high sodium levels, and exposure to BPA from can linings. The heat-intensive canning process can also alter the nutritional content and flavor profile of the fish, while certain species and preparation methods carry additional risks, such as histamine formation.

Key Points

Heavy Metal Exposure: Canned fish, especially larger varieties like albacore tuna, can contain high levels of mercury and other heavy metals that can pose health risks, particularly for pregnant women and children.
Excessive Sodium: Many canned fish products are packed in brine or sauces containing significant amounts of salt, which can contribute to high blood pressure and other health issues for those sensitive to sodium.
BPA in Can Linings: The epoxy resin lining of some cans contains Bisphenol A (BPA), an endocrine-disrupting chemical that can leach into the food and has been linked to various health concerns.
Loss of Nutrients: The high-temperature canning process can reduce the content of certain heat-sensitive nutrients, such as some B vitamins.
Risks of Gout and Allergies: The high purine content in oily fish like sardines can trigger gout attacks, while thermally stable allergens can still affect individuals with fish allergies.
Microplastic Presence: Small canned fish, like sardines, can contain microplastics absorbed from polluted marine environments, presenting an emerging health concern.

Heavy Metal Contamination

One of the most significant concerns surrounding canned fish is the potential for heavy metal contamination, primarily mercury. Mercury from industrial and volcanic activity pollutes waterways, where it is absorbed by fish. Larger, longer-living predatory fish, like albacore or bluefin tuna, bioaccumulate higher levels of methylmercury, a neurotoxin particularly dangerous for developing brains in fetuses and young children. Although authorities set safe consumption limits, these levels can sometimes be exceeded, and individual cans can vary. For example, one can of albacore tuna can contain more than twice the mercury of a can of skipjack or 'chunk light' tuna.

Beyond mercury, other toxic elements can be present. Studies have detected cadmium, lead, and arsenic in various canned fish products. The level of contamination often depends on the fish's species, its origin, and farming practices. Continuous monitoring is essential to ensure contaminants remain within acceptable limits, though complete elimination is difficult.

High Sodium and Preservative Content

Many canned fish products use high levels of sodium for preservation and to enhance flavor. A single can of salmon or sardines can contain a significant portion of a person's recommended daily sodium intake. Excessive sodium consumption is linked to health issues like high blood pressure, heart disease, and kidney problems, especially for those with pre-existing conditions or salt sensitivity. Those watching their sodium intake should be vigilant about reading nutrition labels, as the sodium content varies dramatically between brands and packing liquids (e.g., brine vs. spring water). Rinsing canned fish packed in brine can help reduce some of the salt content.

Bisphenol A (BPA) and Other Packaging Chemicals

Most canned products are lined with an epoxy resin to prevent the can's metal from corroding and interacting with the food. This resin often contains Bisphenol A (BPA), a chemical that can leach into the food. BPA is an endocrine-disrupting chemical linked to a range of potential health concerns, including hormonal disruptions and increased risk of cardiovascular issues. As consumer awareness has grown, some manufacturers have adopted 'BPA-free' can linings. However, this has led to the use of alternative bisphenols, like BPS, whose long-term health effects are still under investigation. To minimize exposure, consumers can look for BPA-free labeling or choose alternative packaging like pouches or glass jars.

Potential Loss of Nutrients

The heat-intensive canning process is essential for sterilizing the product and ensuring a long shelf life. However, this high-temperature processing can degrade certain heat-sensitive vitamins and minerals. While protein and omega-3 fatty acids generally remain stable, levels of specific B vitamins can be significantly reduced. This means that while canned fish is still a nutritious option, it may not offer the same full spectrum of nutrients as its fresh or frozen counterpart.

Comparison: Fresh vs. Canned Fish


Feature	Fresh Fish	Canned Fish
Sodium Content	Naturally low; depends on preparation.	Often very high due to salt used in preservation.
Heavy Metals	Risk is dependent on species and source, but typically lower levels.	Bioaccumulation in certain species (like albacore tuna) can lead to higher levels.
BPA/Chemicals	No risk from can linings.	Potential for BPA or other bisphenols to leach from can linings.
Nutrient Profile	Optimal, with maximum retention of heat-sensitive vitamins.	Some heat-sensitive vitamins (e.g., B vitamins) may be reduced during processing.
Texture & Flavor	Firm, delicate texture and fresh flavor.	Softer texture and often a saltier, more processed taste.
Convenience	Requires preparation and cooking; short shelf life.	Ready-to-eat; long shelf life; very convenient.
Cost	Generally more expensive, especially for certain species.	Very affordable and cost-effective.

Other Safety and Health Considerations

Beyond chemical concerns, other risks are associated with canned fish:

Histamine Poisoning: If fish is not handled properly before canning, it can develop high levels of histamine, a heat-stable toxin that can cause allergic-like reactions such as flushing, headache, and dizziness. Strict quality controls in modern processing have made this less common but it remains a potential risk with improper handling.
Purine Content: For individuals with gout or kidney issues, oily fish like sardines and anchovies are high in purines, which can increase uric acid levels and trigger attacks. These individuals should limit consumption or opt for low-purine alternatives.
Microplastics: Emerging research indicates that microplastics can be found in seafood, and environmental contaminants can increase microplastic content in marine life. Since small fish like sardines are canned whole, consuming them can lead to microplastic exposure, though the long-term health effects are not yet fully understood.
Allergenicity: For some individuals with fish allergies, the thermally stable allergens in fish, like parvalbumin, can still trigger allergic reactions even after the canning process.

How to Minimize the Risks

To enjoy the benefits of fish while minimizing the potential downsides, consider these strategies:

Choose Smaller Fish: Opt for smaller species like sardines or skipjack tuna, which have lower mercury levels than larger fish such as albacore.
Select Low-Sodium Options: Look for cans explicitly labeled as 'low sodium,' 'no salt added,' or packed in water rather than brine.
Buy BPA-Free: Choose brands that use BPA-free can linings or opt for fish packaged in glass jars or pouches.
Vary Your Intake: Rotate your sources of fish and protein to avoid excessive exposure to a single type of contaminant. Consider fresh or frozen fish as part of a balanced diet.
Rinse Canned Fish: If high sodium is a concern, rinsing the fish after draining can help reduce some of the salt content.
Check Can Condition: Never consume canned fish from dented, damaged, swollen, or rusty cans, as this can indicate potential contamination.

For a detailed overview of the quality and safety of canned fish, see the review published by the National Institutes of Health. [^1.3.4]

Conclusion

While convenient and economical, canned fish has several potential downsides that warrant consideration. These include the risk of heavy metal contamination, particularly mercury in larger species like albacore tuna, high sodium content in many products, and the presence of BPA from can linings. The high-heat canning process can also lead to a loss of some nutrients and alter the fish's texture. By choosing smaller fish species, opting for low-sodium or BPA-free products, and varying your seafood sources, you can mitigate many of these risks while still enjoying the nutritional benefits that fish offers.

Frequently Asked Questions

Yes, mercury poisoning is a potential risk, especially from larger species like albacore tuna, which bioaccumulate higher levels of methylmercury. For average adults, moderate intake (one to two cans of lighter tuna per week) is generally safe, but pregnant women, breastfeeding mothers, and young children are advised to limit or avoid high-mercury fish.

To reduce high sodium, choose canned fish packed in water or labeled 'no salt added'. For fish packed in brine, rinsing it thoroughly in a colander after draining can also help remove some of the excess salt.

BPA (Bisphenol A) is a chemical used in the epoxy resin lining of cans to prevent corrosion. It can leach into food, acting as an endocrine disruptor that may interfere with hormones. Manufacturers are now offering BPA-free alternatives, though some are replacing it with other bisphenols.

The high-heat canning process can cause a reduction in certain heat-sensitive vitamins, such as some B vitamins. However, key nutrients like protein and omega-3 fatty acids generally remain stable.

If you have gout or are susceptible to it, you should be cautious with canned sardines. They are high in purines, which break down into uric acid and can exacerbate gout symptoms.

While modern canning is very safe, improper handling before processing can lead to histamine formation, causing a form of food poisoning. Only consume fish from properly sealed, undamaged cans.

Yes, farmed fish like some salmon or shrimp can be a concern. Some unregulated farming practices may use antibiotics, and farmed fish can contain higher levels of PCBs and dioxins. Choosing wild-caught, sustainably sourced fish can mitigate these risks.

Microplastics are tiny plastic particles that enter the marine food web through pollution. Small fish like sardines, which are consumed whole, may contain microplastics, though the health implications are still being studied.