Tuna is one of the most nutrient-dense fish you can eat. A 3.5-ounce serving of fresh yellowfin tuna has roughly 92 calories and nearly 20 grams of protein with less than 1 gram of fat. But protein is just the starting point. Tuna is packed with omega-3 fatty acids, several vitamins and minerals in unusually high concentrations, and a complete set of essential amino acids.
Protein and Calories
Tuna is almost pure protein. That 3.5-ounce serving delivers about 20 grams of it, which is comparable to chicken breast but with fewer calories. The fat content is minimal in lean varieties like yellowfin and skipjack, sitting under 1 gram per serving. This makes tuna one of the highest protein-to-calorie ratios you’ll find in any whole food.
Tuna also provides all nine essential amino acids your body can’t make on its own, making it a complete protein. This matters if you’re relying on tuna as a primary protein source for muscle repair, recovery, or general nutrition.
Omega-3 Fatty Acids
The type of tuna you choose makes a big difference in omega-3 content. Albacore tuna contains about 1,300 milligrams of omega-3s per 3.5-ounce serving, with roughly 1,000 mg coming from DHA and 300 mg from EPA. These are the two omega-3 forms your body uses most readily for brain function, heart health, and controlling inflammation.
Other varieties like skipjack (the most common canned “light” tuna) contain significantly less, closer to 400-500 mg of total omega-3s per serving. If you’re eating tuna specifically for omega-3s, albacore gives you roughly three times more than skipjack.
Vitamins and Minerals
Tuna stands out for a few micronutrients that are hard to get from other foods. A single 3.5-ounce serving of bluefin tuna delivers about 250% of the recommended daily intake of vitamin D, a nutrient most people fall short on. It also provides roughly 149% of the daily selenium recommendation (82 micrograms per 100 grams), and selenium plays a key role in thyroid function and protecting cells from damage.
Vitamin B12 is another strength. A serving contains about 5 micrograms, which is double the daily reference intake. B12 is essential for nerve function and red blood cell production, and it’s found almost exclusively in animal foods. Tuna also supplies about 200 mg of phosphorus per serving, covering roughly 29% of daily needs, which supports bone health and energy metabolism.
Canned in Water vs. Oil
How tuna is packed changes its nutritional profile more than you might expect. Per ounce, canned tuna in oil has 56 calories and 2 grams of fat, while canned tuna in water has just 24 calories and less than 1 gram of fat. That’s more than double the calories from the oil alone.
Here’s the counterintuitive part: water-packed tuna actually retains more omega-3s. An ounce of water-packed tuna contains 56 mg of DHA compared to just 29 mg in oil-packed tuna. The vegetable oil used in canning likely displaces some of the fish’s natural omega-3 fats during processing. If you want the most nutritional value per calorie, water-packed tuna is the better choice.
Mercury Content
Tuna contains mercury, and the amount varies by species. Canned light tuna (usually skipjack) averages 0.126 parts per million, according to FDA testing. Canned albacore (“white” tuna) averages 0.350 ppm, nearly three times higher. Bigeye tuna has the highest mercury levels of any commonly sold tuna and is classified by the FDA as a “choice to avoid.”
For most adults, the FDA recommends eating 8 or more ounces of seafood per week as part of a healthy diet. Canned light tuna falls into the “best choices” category, meaning two to three servings a week is considered safe. Albacore and yellowfin are rated as “good choices,” with a recommended limit of one serving per week. If you’re pregnant or breastfeeding, the guidance is 8 to 12 ounces per week total from lower-mercury options, with a single serving defined as 4 ounces.
Histamine Risk From Improper Storage
Tuna carries a specific food safety concern that most other proteins don’t. Its dark meat is naturally high in an amino acid called histidine. When tuna is stored above 40°F (4°C) after being caught, bacteria convert histidine into histamine. Properly stored tuna contains less than 0.1 mg of histamine per 100 grams. Mishandled tuna can reach 20 to 50 mg per 100 grams, enough to cause a reaction called scombroid poisoning.
Symptoms resemble an allergic reaction: flushing, headache, stomach cramps, and sometimes hives, typically starting within minutes to hours of eating the fish. Cooking does not destroy histamine once it’s formed, so the key prevention step happens before the tuna reaches your kitchen. Fresh tuna should smell clean, not fishy or ammonia-like, and it should have been kept consistently cold from catch to sale.