A can of sardines and a can of tuna seem to solve the exact same problem: open, drain and have protein ready in a minute. And on protein, they really are very close. The comparison changes once you look at what comes with those grams of protein.
For protein, it is essentially a practical tie. Sardines pull ahead for EPA and DHA, calcium when the bones are eaten and very low mercury. Water-packed tuna can be much leaner, but not every type of tuna has the same profile.
A useful comparison of drained canned fish
Exact values vary by species and packing liquid, so representative ranges are more useful than pretending every can is nutritionally identical.
| Per 100 g drained | Sardines | Canned light tuna in water |
|---|---|---|
| Protein | ~24–25 g | ~25–26 g |
| Fat | ~10–12 g | ~1 g |
| EPA + DHA | ~1.3–1.5 g | ~0.2 g |
| FDA average mercury | ~0.01 ppm | ~0.13 ppm |
Protein differs by only a gram or two per 100 grams. Omega-3 is the opposite: a serving of sardines can provide six or seven times as much EPA+DHA as canned light tuna in water.
In a drained 3- to 4-ounce serving, both remain substantial protein foods. The practical choice is rarely about one extra gram of protein and more often about fat, omega-3, calcium, sodium, tuna species and how often the fish is eaten.
Tuna is leaner; sardines bring more fat with a different role
Water-packed tuna is usually very low in fat and therefore lower in calories. Sardines contain much more, especially when packed in oil. That does not make the difference simply “good” or “bad”: some of that fat includes EPA and DHA.
Packing oil matters too. Undrained sardines in oil are not a fair match for thoroughly drained tuna in water because some of the calorie difference would come from the added oil rather than the fish itself.
When comparing two cans at the store, use the drained serving and the Nutrition Facts panel if available. Oil-packed fish can still fit well; it simply has a different energy profile from a water-packed product.
For omega-3, the gap is no longer small
NIH data list about 1.19 grams of EPA+DHA in 3 ounces of drained canned sardines in tomato sauce, which works out to roughly 1.4 grams per 100 grams.
Canned light tuna in water provides about 0.19 gram per 3 ounces, or roughly 0.22 gram per 100 grams. Sardines are not ahead by a rounding error; they can provide several times as much.
That makes sardines especially useful when the goal is not only convenient protein but also a meaningful amount of long-chain omega-3 in a relatively small serving.
Mercury separates them too
FDA commercial-fish data put sardines at an average of about 0.01 ppm mercury. Canned light tuna averages around 0.13 ppm, canned albacore about 0.35 ppm, yellowfin about 0.35 ppm and bigeye about 0.69 ppm.
That is why “tuna” is too broad a word when mercury is the question. The species and product matter.
For people who are pregnant, breastfeeding or feeding young children, FDA/EPA advice distinguishes tuna types rather than treating all tuna alike. A canned-light product and a bigeye tuna steak are not interchangeable mercury choices.
Soft sardine bones change the calcium picture
In many canned sardines the bones are soft enough to eat, and that creates a nutritional advantage tuna does not share. A 3-ounce serving can provide roughly 300 mg or more of calcium, while boneless canned tuna provides very little.
That does not make sardines better at everything, but it does show why protein alone misses an important part of the comparison.
Which one deserves pantry space?
Both do. Water-packed tuna offers a lot of protein with very little fat and a mild flavor that fits easily into many meals. Sardines provide nearly the same protein while adding far more EPA+DHA, calcium when the bones are eaten and a very low mercury profile.
Sodium also varies substantially by brand and packing liquid. Two cans with similar protein can differ enough in sodium that the label matters more than the species name for that particular nutrient.
If protein is the only metric, they are basically tied. If you look at the whole package, sardines bring several advantages the protein number does not show.
Sources
- USDA FoodData Central — Protein, fat and canned fish composition.
- NIH Office of Dietary Supplements — Omega-3 Fatty Acids — EPA and DHA in sardines and tuna.
- FDA/EPA — Advice about Eating Fish — Mercury-based fish-choice categories.
- FDA — Technical Information on Mercury in Commercial Fish — Average mercury concentrations by fish and tuna type.