Oily Fish vs. White Fish: Defining the Difference
At the heart of the matter is the fundamental difference in how various fish store their fat. Oily fish, also known as fatty fish, have oil distributed throughout their body tissues and belly cavity. This is where the majority of their beneficial long-chain omega-3 fatty acids are found. This category includes fish like salmon, mackerel, herring, and sardines. By contrast, white fish store most of their oil in their liver, which means their flesh is considerably leaner. Examples of white fish include cod, haddock, and plaice.
Why Canned Tuna Doesn't Make the Cut
For many years, some types of tuna, particularly when fresh, were included on lists of oily fish. However, public health organizations, such as the UK's National Health Service (NHS) and the British Heart Foundation (BHF), have revised their guidelines. In the UK, for instance, official advice changed in 2018 because data revealed that the omega-3 content in fresh tuna was more comparable to that of white fish.
The Impact of the Canning Process
The processing method used for canned tuna is a primary reason it is not considered an oily fish. Unlike canned salmon or sardines, which are often cooked only once inside the can, most tuna is pre-cooked before canning. This steaming process, along with subsequent draining, significantly reduces the levels of the long-chain omega-3 fatty acids (EPA and DHA) in the final product. While tuna still contains some omega-3s, the concentration is too low to meet the criteria for classification as an oily fish.
The Nutritional Tale of Two Tunas: Water vs. Oil
When choosing canned tuna, the packing liquid can make a noticeable difference in the final nutritional profile. However, it's important to be aware of how this affects the omega-3 content.
| Nutrient (per 1 oz) | Canned in Oil | Canned in Water |
|---|---|---|
| Total Fat | 6.4g* | 0.8g* |
| Omega-3 (DHA) | 29mg | 56mg |
| Omega-3 (EPA) | 8mg | 8mg |
| Protein | 8g | 6g |
| Vitamin D | 1.9µg | 0.3µg |
| Sodium | 118mg | 70mg |
*Note: Nutritional information can vary by brand and specific product. The table above provides an example based on available data.
Interestingly, data from one source indicates that canned tuna packed in water contains a higher level of DHA per ounce than oil-packed tuna. This is because tuna packed in oil is drained, and the omega-3s lost during cooking are discarded along with the oil. In water-packed versions, these omega-3s are retained in the canning liquid, but many people drain it before eating. If you discard the water or oil, you are also discarding some of the valuable fatty acids.
Beyond Omega-3s: The Other Nutritional Benefits of Tuna
Just because canned tuna is not an oily fish doesn't mean it isn't healthy. Canned tuna remains a highly nutritious food with many health benefits, including:
- High-Quality Protein: Tuna is a complete protein, meaning it contains all the essential amino acids your body needs for muscle repair and growth.
- Essential Vitamins and Minerals: It is an excellent source of B vitamins (especially B3 and B12), as well as selenium, magnesium, and vitamin D.
- Low in Fat: Canned tuna, particularly when packed in water, is a very lean source of protein and is low in calories, making it useful for weight management.
Which Tuna is the Best Choice for You?
When selecting canned tuna, consider the type of tuna and the packing liquid based on your nutritional goals:
- Skipjack Tuna: Most canned "light" tuna is skipjack. It is a smaller species, which means it tends to have lower mercury levels.
- Albacore Tuna: Often sold as "white" tuna, albacore has a milder flavor but is a larger fish and thus generally higher in mercury.
- Tuna in Water vs. Oil: If you want to control your calorie and sodium intake, opt for tuna packed in water and choose a low-sodium version. For a more satisfying flavor and moisture content, tuna in oil is an option, but be mindful of the added calories and fat. The choice also impacts omega-3 retention, as discussed above.
How to Supplement Your Diet with Oily Fish
If your goal is to consume adequate omega-3 fatty acids, relying solely on canned tuna is not the most effective strategy. Instead, consider incorporating these true oily fish into your diet:
- Salmon
- Mackerel
- Sardines
- Herring
- Trout
- Pilchards
These fish provide a much more concentrated source of EPA and DHA compared to canned tuna. You can also find some of these options, like salmon, sardines, and mackerel, conveniently in cans, ensuring a higher omega-3 intake than canned tuna. The British Heart Foundation provides helpful guidance on heart-healthy ways to include oily fish in your diet.
Conclusion: Understanding the Distinction
Ultimately, canned tuna does not count as an oily fish because of the pre-canning cooking process that reduces its omega-3 content. This reclassification, adopted by major health authorities, highlights the importance of sourcing omega-3s from a variety of fish. While not an oily fish, canned tuna remains a convenient, affordable, and nutritious staple, providing lean protein and other essential vitamins and minerals. For those aiming to meet their omega-3 needs, it's wise to diversify their fish intake with true oily fish like salmon, sardines, and mackerel.
