Tuna is exceptionally high in protein, delivering about 26 grams per 100-gram serving with almost no carbohydrates and very little fat. It’s also a rich source of omega-3 fatty acids, selenium, vitamin D, and several B vitamins, making it one of the most nutrient-dense fish you can eat.
Protein
Protein is tuna’s standout nutrient. A standard can of light tuna (165 grams, drained) provides roughly 42 grams of complete protein, meaning it contains all nine essential amino acids your body can’t make on its own. That’s close to an entire day’s worth for many adults, packed into a single can. By calorie count, about 93% of the energy in water-packed tuna comes from protein, with fat contributing just 7% and carbohydrates essentially zero. At 116 calories per 100 grams, it’s one of the leanest protein sources available.
Omega-3 Fatty Acids
Despite being low in total fat, tuna provides meaningful amounts of EPA and DHA, the two omega-3 fats linked to heart and brain health. The amount varies significantly by species. Bluefin tuna leads with about 1.6 grams of combined EPA and DHA per 100 grams of fish. Albacore follows at roughly 1.3 grams, while lighter varieties like skipjack come in around 0.5 grams.
How tuna is packed matters too. Water-packed canned tuna retains nearly twice the DHA of oil-packed tuna per ounce (56 mg versus 29 mg), because draining oil-packed tuna pulls some omega-3s out with the oil. If omega-3s are what you’re after, water-packed is the better choice.
Vitamin D
Tuna is one of the few foods naturally rich in vitamin D. Just 3 ounces of canned tuna supplies up to 50% of the recommended daily level. Since most people get their vitamin D from sunlight and relatively few foods contain it in significant amounts, tuna is a practical way to fill the gap, especially during winter months or for people who spend most of their time indoors.
Selenium
Tuna is loaded with selenium, a mineral that supports thyroid function and acts as an antioxidant in the body. Selenium also plays an interesting role in relation to mercury, one of the concerns people have about eating tuna. Your body uses selenium-dependent enzymes to prevent and repair oxidative damage, particularly in the brain. Mercury can bind to selenium and disable those enzymes, but this only becomes a problem when mercury levels exceed selenium levels in the fish. In tuna, selenium consistently outweighs mercury by a wide margin. Researchers at Oregon State University found that all four tuna species they studied had strongly positive “health benefit values,” meaning they supply far more protective selenium than harmful mercury. Skipjack tuna had the highest benefit ratio of any species in the study.
Mercury Levels by Tuna Type
Mercury is worth understanding because it varies dramatically between tuna species, and it determines how much you can safely eat each week. According to FDA testing data, canned light tuna (typically skipjack) averages 0.126 parts per million of mercury. Canned albacore (white tuna) averages 0.350 ppm, nearly three times higher. Fresh or frozen albacore is similar at 0.358 ppm.
The FDA classifies tuna into three tiers based on these levels:
- Best Choice: Canned light tuna, including skipjack. You can eat 2 to 3 servings per week.
- Good Choice: Albacore (white) tuna, canned or fresh, and yellowfin. Limit to 1 serving per week.
- Avoid: Bigeye tuna, which has the highest mercury levels of any tuna species.
For pregnant or breastfeeding women, the FDA recommends 8 to 12 ounces of lower-mercury seafood per week, with a serving size of 4 ounces. Children’s portions are smaller: about 1 ounce for toddlers, scaling up to 4 ounces by age 11, with 2 servings per week from the “Best Choice” list.
Other Vitamins and Minerals
Beyond the headliners, tuna provides niacin (vitamin B3), which helps convert food into energy, and vitamin B12, essential for nerve function and red blood cell production. It contains phosphorus for bone health and small amounts of iodine, though at 7 micrograms per 3-ounce serving, tuna isn’t a major iodine source compared to cod (146 mcg) or dairy products.
Water-Packed vs. Oil-Packed
Choosing between water-packed and oil-packed tuna changes the nutritional profile more than you might expect. Per ounce, oil-packed tuna has about 2.5 times the total fat of water-packed (2.3 grams versus 0.9 grams), mostly from the added oil rather than the fish itself. And as noted above, draining oil-packed tuna strips away a significant portion of its DHA. Water-packed tuna keeps more of its natural omega-3s intact while staying leaner overall. Oil-packed tuna does have a richer taste and softer texture, so the trade-off is partly about preference, but nutritionally, water-packed comes out ahead.