The Primary Concerns with Canned Tuna
Canned tuna is a convenient source of protein and heart-healthy omega-3 fatty acids, but it comes with several potential downsides, most notably mercury contamination. The level of mercury can vary significantly depending on the species of tuna. In addition, processing methods can impact the final nutritional profile, including sodium and fat content. Understanding these factors is essential for making informed choices that protect your health and support environmental sustainability.
Mercury Levels: Which Tuna Species Are Safest?
Mercury naturally accumulates in seawater and, through a process called bioaccumulation, ends up in fish. As a predatory fish eats smaller ones, the mercury compounds accumulate and magnify. Larger, longer-living fish at the top of the food chain tend to have the highest mercury concentrations.
- Bigeye Tuna: Often used for high-end sushi, bigeye tuna is one of the largest tuna species and has the highest mercury levels. It should be avoided, especially by vulnerable groups.
- Albacore (White) Tuna: This is a larger species than skipjack and therefore accumulates more mercury over its lifespan. While a good source of omega-3s, its consumption should be more limited than light tuna.
- Yellowfin Tuna: This species has mercury levels similar to albacore. If purchasing canned, check if it's labeled 'gourmet' or 'tonno,' as this can indicate a higher mercury content.
- Skipjack (Light) Tuna: The smallest and most abundant commercial tuna species, skipjack has the lowest mercury levels. It is the safest choice for frequent consumption and is widely used in canned 'chunk light' tuna products.
Sodium and Packing Liquid
Beyond mercury, the way tuna is canned also impacts its nutritional value. The two most common packing liquids are oil and water, and the sodium content can vary dramatically between brands and varieties.
- Sodium Content: Tuna is not naturally high in sodium, but a significant amount is often added during the canning process for flavor and preservation. A single can can contain a large percentage of your daily recommended sodium intake. For those on a low-sodium diet, it is critical to seek out products specifically labeled 'low sodium' or 'no salt added'.
- Water vs. Oil-Packed: Water-packed tuna is lower in calories and fat compared to oil-packed varieties. While some oil-packed tuna uses healthful olive oil and can retain more omega-3s if the oil is consumed, most common varieties are packed in cheaper vegetable oils. When drained, water-packed tuna retains more omega-3 fatty acids compared to drained oil-packed tuna, as omega-3s are fat-soluble and can drain away with the oil.
Sustainability and Fishing Methods
Consumer choice affects the health of our oceans. Unsustainable fishing practices can lead to bycatch (unintentionally catching other marine species like turtles or sharks) and overfishing.
- Best Practices: Look for tuna caught using "pole-and-line," "troll-caught," or "FAD-free" (fish aggregating device-free) methods. These methods have minimal environmental impact and virtually eliminate bycatch. Certification labels like the Marine Stewardship Council (MSC) are excellent indicators of sustainability.
- Less Sustainable Practices: Avoid tuna caught using conventional purse seines with FADs or destructive longlines, which can harm other marine life. The common "Dolphin-Safe" label, while positive, does not ensure overall sustainability.
Comparison of Canned Tuna Varieties
| Feature | Bigeye Tuna | Albacore (White) Tuna | Skipjack (Light) Tuna |
|---|---|---|---|
| Mercury Content | Very High | High | Low |
| FDA/EPA Recommendation | Avoid | Limit to 1 serving/week for adults | Best Choice: 2-3 servings/week for adults |
| Flavor Profile | Rich, sweet, firm texture | Mild, delicate, firm texture | Stronger, more "fishy" flavor, flaky texture |
| Packing Liquid | Typically fresh or frozen | Water or oil | Water or oil |
| Sustainability | Varies by fishery, Atlantic stock overfished | Some sustainable fisheries exist, check label for method | Most abundant and best-managed stock |
Making Safer Canned Tuna Choices
- Prioritize skipjack or canned light tuna: Due to their lower mercury content, these varieties are the safest choice for regular consumption.
- Check for low-sodium options: If monitoring sodium intake, always select cans specifically marked 'low sodium' or 'no salt added'.
- Rinse your tuna: Rinsing canned tuna under water can help remove some of the surface-level sodium.
- Choose water-packed tuna: For lower calories and a cleaner flavor, choose tuna packed in water over oil. If you desire the benefits of olive oil-packed tuna, consider a high-quality brand where the oil is meant to be consumed with the fish.
- Look for sustainable certifications: Choose tuna with clear labels indicating sustainable fishing methods, such as 'pole-and-line caught' or MSC-certified, to support ethical practices.
Conclusion
By being an informed consumer, you can easily navigate the canned tuna aisle to make healthier, safer, and more sustainable choices. Avoiding the larger, high-mercury species like bigeye and limiting albacore is the most important step for health, especially for sensitive populations. When paired with choosing low-sodium, water-packed varieties from sustainably-minded brands, you can enjoy this nutritious protein source with confidence. Remember to consume tuna in moderation and diversify your seafood choices with other low-mercury options like salmon and sardines to maximize nutritional benefits and minimize risks.
For more detailed information on sustainable seafood and specific recommendations, consult reputable resources like the Monterey Bay Aquarium Seafood Watch guide.
