Tuna is one of the most nutrient-dense proteins you can eat, delivering high-quality protein, omega-3 fatty acids, and selenium in a low-calorie package. A single 3-ounce serving of cooked skipjack tuna provides nearly 2 grams of leucine (the amino acid most responsible for triggering muscle repair) along with protective fats that benefit your heart, brain, and eyes.
Protein That Builds and Repairs Muscle
Tuna is a lean, complete protein, meaning it contains all nine essential amino acids your body can’t make on its own. What sets it apart from many other protein sources is its exceptionally high leucine content. A 3-ounce serving of fresh skipjack tuna delivers about 1.95 grams of leucine, and the same portion of canned white tuna in oil provides roughly 1.83 grams. Leucine is the amino acid that flips the switch on muscle protein synthesis, the process your body uses to rebuild and grow muscle tissue after exercise or injury.
That leucine concentration matters because research consistently shows a threshold of about 2 to 3 grams per meal is ideal for maximizing muscle repair. A serving of tuna gets you most of the way there on its own, making it a practical choice for athletes, older adults trying to preserve muscle mass, and anyone recovering from physical stress.
Omega-3 Fats for Heart and Blood Vessel Health
The omega-3 fatty acids in tuna, specifically EPA and DHA, are the forms your body uses most efficiently. Canned light tuna packed in water provides about 0.17 grams of DHA and 0.02 grams of EPA per 3-ounce serving. Yellowfin tuna is leaner, coming in at 0.09 grams of DHA and 0.01 grams of EPA for the same portion. These numbers are modest compared to salmon, but tuna’s accessibility and low cost make it easy to eat regularly, which is what matters most for long-term cardiovascular benefit.
EPA and DHA help lower triglyceride levels, reduce inflammation in blood vessel walls, and support healthy blood pressure. They also make blood platelets slightly less sticky, which can reduce the risk of clot formation. Eating two to three servings of fish per week is the general target most nutrition guidelines recommend, and tuna is one of the simplest ways to hit that goal.
How Selenium Protects Your Brain
Tuna is one of the richest dietary sources of selenium, a trace mineral that plays a surprisingly specific role in brain health. Selenium is essential for producing a family of proteins called selenoproteins, which act as your cells’ defense system against a particular type of damage called ferroptotic cell death. This happens when iron accumulates in cells and triggers a chain reaction of destruction to cell membranes.
Your brain is especially vulnerable to this kind of damage because it’s rich in both iron and the types of fats that are easily oxidized. Selenium helps your neurons produce an antioxidant (GPX4) that directly neutralizes this process. In animal models of stroke, selenium drove significant changes in the expression of hundreds of genes involved in cell protection, including genes that maintain mitochondrial function. While these findings come from lab research, they help explain why populations with higher selenium intake tend to show better cognitive outcomes as they age.
Keeping Your Eyes Healthy
The omega-3s in tuna also play a direct role in eye health. Your eyes depend on a multi-layered tear film to stay lubricated and protected: a lipid layer that prevents evaporation, a protein layer that nourishes the cornea, and a mucous layer for continuous lubrication. When this system breaks down, you get dry eye syndrome, which affects tens of millions of adults.
EPA and DHA contribute to the fatty acid content of tear secretions, improving tear film quality and reducing evaporative loss. They also block inflammatory signals at the surface of the eye, which is relevant because chronic low-grade inflammation is a major driver of dry eye symptoms. Clinical trials on omega-3 supplementation have shown meaningful improvements: in one study, patients saw symptom scores improve by more than 9 points within a single month, while a placebo group actually got slightly worse. Eating cold-water fish like tuna, salmon, and sardines regularly helps raise omega-3 levels enough to support these benefits without supplements.
Canned in Water vs. Oil
How your tuna is packed changes its nutritional profile more than most people realize. A standard 4-ounce serving of tuna canned in water contains about 3.6 grams of fat, while the same serving canned in oil has 9.2 grams, more than double. The oil-packed version is higher in calories as a result. If you’re watching your overall fat or calorie intake, water-packed tuna is the straightforward choice. If you’re less concerned about calories and prefer the richer flavor and texture, oil-packed tuna is still a nutritious option.
Mercury: Which Types Are Safest
Mercury is the main reason people hesitate about eating tuna, and the concern is legitimate, but it varies dramatically by species. Skipjack tuna (sold as “canned light”) contains mercury levels below 0.22 parts per million, which puts it in the FDA’s “Best Choices” category. You can safely eat two to three servings per week. Albacore (sold as “canned white”) and yellowfin exceed that 0.22 ppm threshold and fall into the “Good Choices” tier, meaning one serving per week is the recommended limit. Bigeye tuna, often found in sushi restaurants, carries the highest mercury levels of any tuna species and is the only type the FDA says to avoid entirely.
For pregnant and breastfeeding women, the FDA recommends 2 to 3 servings per week from the Best Choices list (with one serving being 4 ounces) or 1 serving from the Good Choices list. Children need smaller portions: about 1 ounce per serving for ages 1 to 3, scaling up to 4 ounces by age 11, with 2 servings per week from the Best Choices list.
The practical takeaway is simple. Canned light tuna gives you the protein, omega-3s, and selenium benefits with the lowest mercury exposure. If you prefer albacore for its milder flavor and firmer texture, just keep it to once a week and fill remaining fish servings with lower-mercury options.