Understanding the Distinction Between Lean and Fatty Fish
To understand why canned tuna does not qualify as a fatty fish, it's essential to know the official distinction. Fish are categorized as either lean (whitefish) or fatty (oily) based primarily on their fat content and the location of that fat. Fatty fish store their oil throughout their muscle tissue, which is why their flesh is darker. This oil is rich in long-chain omega-3 polyunsaturated fatty acids (EPA and DHA), which are highly beneficial for heart, brain, and eye health. Examples of true fatty fish include:
- Salmon
- Mackerel
- Sardines
- Herring
- Anchovies
In contrast, lean fish store most of their fat in their liver, resulting in white, flaky, and low-fat muscle tissue. Cod, haddock, and flounder are classic examples of lean fish. Despite being from the same family, most canned tuna falls into this lean category for a few key reasons related to the specific species used and the canning process itself.
The Species and Processing That Change Tuna's Fat Profile
The perception of all tuna being oily is a common misconception. The type of tuna used for canning is typically different from the fresh steaks one might find at a high-end restaurant. Most "light" canned tuna is made from the smaller skipjack tuna, which is naturally a leaner species. Even canned "white" albacore tuna, while slightly higher in omega-3s than skipjack, is still not considered a fatty fish after processing.
Another critical factor is the canning process. To make the fish shelf-stable, it undergoes a high-heat sterilization process. This can cause some of the natural fish oils, and thus the omega-3s, to be cooked out. While fresh tuna can be high in omega-3s, the canning process effectively reduces the levels to those more comparable with white fish. This is a key reason why health organizations, including the UK's NHS, state that canned tuna is not an oily fish.
Canned Tuna vs. True Fatty Fish: A Nutritional Comparison
To illustrate the difference, let's compare the nutritional profile of a serving of canned tuna with a well-known fatty fish, salmon. The differences in fat, omega-3, and caloric content are clear. For this comparison, we will use a 3-ounce portion of canned light tuna packed in water and a similar portion of canned pink salmon, which is also a good source of omega-3s.
| Nutrient (per 3 oz serving) | Canned Light Tuna (in water) | Canned Pink Salmon |
|---|---|---|
| Total Fat | <1 g | ~5 g |
| Omega-3s (EPA + DHA) | ~190 mg | ~910 mg |
| Calories | ~73 kcal | ~118 kcal |
| Protein | ~17 g | ~19 g |
Note: Nutritional values can vary between brands. EPA+DHA values for canned tuna can differ based on species and processing.
As the table shows, a serving of canned salmon provides significantly more omega-3 fatty acids and overall fat than canned tuna. This is the primary reason for the different classifications. Canned tuna is an excellent source of lean protein, but it is not the best choice if you are trying to increase your omega-3 intake.
What Kind of Tuna Should You Choose?
The packing liquid—water or oil—also affects the final nutritional content. Tuna packed in oil will have higher overall fat and calorie content due to the added oil. However, some omega-3s can also transfer into the oil, so if you drain it completely, you may lose some of those fats. While water-packed tuna is lower in total fat and calories, some research suggests it may retain more DHA.
Choosing between light (skipjack) and white (albacore) tuna also matters. Albacore generally contains more omega-3s than skipjack. However, larger fish species like albacore also tend to have higher levels of mercury. Health experts often recommend light, skipjack tuna, especially for pregnant women and children, due to its lower mercury content, and to enjoy it in moderation. For detailed guidance on omega-3s, you can consult reputable sources like the National Institutes of Health. [^1]
Conclusion: A Healthy Choice, But Not a Fatty One
In summary, canned tuna is not a fatty fish. It is a lean protein with a low-fat profile, especially when packed in water. The species of tuna typically canned (like skipjack) and the heat processing involved significantly reduce the omega-3 content compared to truly oily fish. While canned tuna still offers important nutrients like protein, vitamin D, and selenium, it should not be relied upon as a primary source of omega-3 fatty acids. For those, you should turn to other fish like salmon, sardines, and mackerel. By understanding the nutritional differences, consumers can make more informed decisions to meet their dietary goals.
[^1]: National Institutes of Health, Office of Dietary Supplements, 'Omega-3 Fatty Acids Fact Sheet for Health Professionals', https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/
Further Reading
For more detailed information on specific fish and their omega-3 content, resources like the National Institutes of Health (NIH) Office of Dietary Supplements provide comprehensive guides. You can find their fact sheet on omega-3 fatty acids at https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/.
