Not all canned tuna is created equal. You’d think a can labeled “tuna” is just… tuna, right? But the species of fish inside that can changes everything — from the taste and texture to something a lot more important: how much mercury you’re putting into your body each week. And that difference is what determines whether your tuna habit is totally fine or quietly becoming a problem.
So what’s actually in those cans?
Most of the canned tuna on American shelves comes from one of two fish. The first is skipjack, a smaller tuna that makes up about 70 percent of canned tuna sold in the U.S. You’ll see it labeled as “chunk light” or “flaked light” tuna. It’s the cheaper option, and it happens to be the safer one too. The second is albacore, which is a bigger fish with a milder flavor. It gets sold as “white tuna” and usually costs a bit more. About 20 percent of canned tuna consumed here is albacore, though that number might have shifted in recent years.
Here’s the thing, though — that size difference between skipjack and albacore isn’t just trivia. Bigger, older fish accumulate more mercury over their lifetimes. So that “premium” white tuna in your pantry? It typically contains three times more mercury than canned light tuna. That’s a pretty significant gap hiding behind nearly identical packaging.
Wait, how does mercury even get in there?
Mercury exists naturally in the environment — volcanoes release it, for instance — but industrial activity has made the problem much worse. Power plants, cement factories, and chemical manufacturers all release mercury into the air. It settles into rivers, streams, and eventually the ocean. Once it’s in the water, natural bacteria convert it into something called methylmercury, and that’s where the food chain gets involved. Small organisms absorb it. Small fish eat those organisms. Bigger fish eat the small fish. And at every step, the mercury concentrations get higher.
Tuna sit pretty high on that chain. A 2023 study found that tuna had the highest mercury content of any fish tested. The mercury doesn’t break down or dissolve once a fish absorbs it — it just builds up. So a big albacore that’s been swimming around for years is essentially a mercury storage device with fins. That’s not meant to scare you away from tuna entirely, but it’s good to know what you’re working with.
The actual weekly limit, broken down
The FDA breaks fish into three categories based on mercury levels: “best choices,” “good choices,” and “choices to avoid.” Canned light tuna (skipjack) falls into the best choices category. The recommendation? You can eat two to three servings per week, which works out to roughly 8 to 12 ounces. In practical terms, that’s about two to three 5-ounce cans. Not bad at all for a protein source that costs a couple bucks per can.
Canned white tuna (albacore) is a different story. Because of its higher mercury levels, the FDA puts it in the “good choices” category and recommends just one serving per week — about 4 ounces for adults. That’s roughly one 5-ounce can. Dr. Michael O’Neill, an internal medicine specialist at Hartford HealthCare, puts it even more conservatively, suggesting the average adult can safely eat six to nine ounces per week total, which works out to about one to two cans depending on size. Either way, eating tuna every single day would push you well past the safe limit.
And what about kids?
Children’s developing brains are more vulnerable to mercury than adult brains. That’s not just a general precaution — mercury can genuinely interfere with how a child’s brain absorbs nutrients during critical growth periods. The FDA says kids can eat fish one to two times per week, using a variety of fish types. But the portion sizes need to be much smaller than what adults eat. For kids ages 2 to 3, a serving is just 1 ounce. Ages 4 to 7 get 2 ounces. Ages 8 to 10 can have 3 ounces. And kids 11 and up can eat an adult-sized 4-ounce serving.
Stick to canned light tuna for kids whenever possible. The FDA specifically warns against giving children bigeye tuna (the kind often used in sushi), and also recommends that children avoid raw fish entirely due to foodborne illness risks. Two servings of canned light tuna per week is considered safe for most children. It’s honestly one of the easier ways to get protein and omega-3s into a kid who won’t touch salmon.
Pregnant? This part is for you.
There’s conflicting advice floating around about whether pregnant women should eat tuna at all. The FDA actually says that people who are pregnant or breastfeeding can eat canned light tuna — two to three servings a week is their recommendation. For white albacore, they suggest limiting it to one serving per week. The benefits of omega-3 fatty acids for fetal development are real, and the FDA apparently considers the mercury levels in light tuna low enough to be worth the trade-off.
However, Dr. O’Neill takes a more cautious stance, suggesting that pregnant or breastfeeding mothers should avoid tuna entirely. High doses of mercury in fetuses can lead to serious problems including cognitive difficulties, cerebral palsy, deafness, and blindness. This is one of those areas where the experts don’t fully agree, so talking to your OB about your specific situation is probably the smartest move. If you want fish but want to play it extra safe, salmon and cod both contain far less mercury than any type of tuna.
What mercury poisoning actually looks like
Mercury poisoning isn’t dramatic or sudden — it creeps up. Methylmercury gets absorbed through your gastrointestinal tract and then distributes itself throughout your body, with a particular affinity for the nervous system and brain. Chronic exposure can cause memory loss, irritability, tingling sensations, tremors, and changes to your taste, vision, and smell. In adults, it can also mess with fertility and blood pressure regulation. None of these symptoms scream “I’ve been eating too much tuna,” which is part of what makes it tricky.
And here’s the frustrating part: once mercury is in your body, it doesn’t leave quickly. Dr. O’Neill notes that it can take weeks or even months for mercury levels to drop after you stop the exposure. There are medications that can help pull mercury out of the body, but for most people, the best treatment is simply stopping the intake. Which, honestly, is kind of unsatisfying when you think about it — there’s no quick fix, just time.
Not all cans are created equal (seriously)
Beyond just “light” versus “white,” the actual mercury content varies from can to can. A 5-ounce can of chunk light tuna made from skipjack typically contains about 20 micrograms of mercury. Albacore and yellowfin? Up to 50 micrograms per can. And then there’s Atlantic bluefin — the big one — which can pack as many as 283 micrograms per five ounces. That’s more than fourteen times the amount in a can of light tuna. The EPA lists the average mercury concentration of canned light tuna at 0.13 parts per million, while canned albacore chunk white tuna comes in at 0.35 parts per million. The FDA considers anything over 0.46 parts per million unsafe for consumption.
Where the fish was caught matters too. Dr. O’Neill recommends buying tuna caught from U.S. or local fisheries, since those tend to be healthier fish from better-monitored waters. He specifically warns against imported tuna, especially from the Indian Ocean. Labels that say “line caught,” “pole caught,” or “FAD-free” (fish aggregating device free) are also good indicators of more sustainable — and generally safer — practices. If the can doesn’t tell you where the fish came from, that’s a red flag.
Oil-packed or water-packed — does it matter?
This one is purely about calories and fat, not mercury. But since people always ask: a can of white tuna in oil (drained) has about 331 calories and 14.4 grams of fat. The same fish packed in water? 220 calories and 5.1 grams of fat. That’s a pretty big difference. For light tuna, oil-packed runs 339 calories and 14 grams of fat, while water-packed drops to 191 calories and just 1.4 grams of fat. If you’re watching your weight or trying to keep things lean, water-packed is the obvious winner.
The mercury levels don’t change based on packing liquid, so pick whichever you prefer from a taste standpoint. Some people swear oil-packed tuna makes better salads and sandwiches. Others don’t notice much difference. Neither choice is wrong — it just depends on what you’re optimizing for.
A handy tool if you want to get specific
The FDA’s guidelines are based on averages — specifically, they’re built around an average American adult weight of 165 pounds. If you weigh less than that, you might want to eat smaller portions or stick to two servings a week instead of three. If you weigh more, you may have slightly more wiggle room, though the FDA doesn’t explicitly say that.
For anyone who wants a more personalized answer, the Environmental Working Group has a tuna calculator that lets you enter your weight, age, gender, and whether you have a heart condition. It then gives you tailored suggestions for the type and amount of fish you can safely eat, along with mercury content and sustainability information. It takes about 30 seconds and it’s genuinely useful if tuna is a regular part of your diet. Also worth checking your state and local advisories — some areas issue specific warnings about certain types of fish based on local water conditions.
The simplest takeaway: if you’re going to eat canned tuna regularly, make it light tuna, keep it to two or three cans a week, and check the label to know what species you’re actually eating.
