Eating 4 cans of tuna a week is generally considered acceptable for adults if it's mostly canned light (skipjack) tuna (low mercury), but it pushes the recommended limits; for albacore tuna (higher mercury), it's too much, and pregnant people should limit it to 1 serving or avoid it. The FDA suggests 2-3 servings (8-12 oz) of low-mercury fish weekly, so 4 cans (often 5oz/can) is pushing that, making variety important.
Tuna contains very high amounts of mercury, and eating too much can cause mercury poisoning. The FDA recommends that a 200 pound male not consume more than 3 cans in a week.
In more severe cases, symptoms such as bronchospasm, respiratory failure, and low blood pressure may be present (vasodilatory shock). Patients with tuna poisoning have symptoms such as diarrhea and abdominal pain.
Here is FDA guidance: According to the FDA, canned light tuna, made primarily from skipjack, is recognized as a fish with low mercury levels and is designated as a "best choice." A serving is typically 4 ounces for adults, per the FDA. The FDA recommends eating two to three servings a week, or about 8 to 12 ounces.
An average tuna fish contains about 0.391 ppm (or 0.391 mg/kg) of mercury. The maximum permitted amount of mercury in tuna in most countries is 1.0 ppm. Evidently, these levels do not differ greatly, but chances of mercury poisoning are still small.
Apparently, the safest tuna to eat is Skipjack.
If you're counting calories and maximizing omega-3 fatty acids, then tuna in water might make a great choice. On the other hand, if moisture, flavor, and vitamin D levels are your focus, then olive oil-packed tuna might be better. Whatever tuna you choose, it's important not to go overboard for this mild-flavored fish.
Fish that eat other fish usually have the most mercury. These include: In the ocean, Shark, Swordfish, King Mackerel, Marlin, Orange Roughy, Tilefish (from the Gulf of Mexico), and Bigeye Tuna. In lakes and rivers, Black Bass species (for example, Largemouth Bass), Striped Bass, Pikeminnow, and White Sturgeon.
Tuna: if you are trying for a baby or are pregnant, you should have no more than 4 cans of tuna a week or no more than 2 tuna steaks a week. This is because tuna contains higher levels of mercury than other fish. If you are breastfeeding, there is no limit on how much tuna you can eat.
Researchers from Chalmers University of Technology have come up with a novel approach to packaging canned tuna infused in the water-based solution of amino acid cysteine. It was shown to remove up to 35 percent of the accumulated mercury in canned tuna, significantly reducing human exposure to mercury via food.
Omega 3s
These are the good fats that keep your heart happy and healthy. Tuna is brimming with two types of omega-3 fatty acids, DHA and EPA, which have been linked to reduced inflammation, improved brain function, and a lowered risk of heart disease.
Some tuna cans that say do not drain because they don't add oil, water, fillers, preservatives, and GMO soy broth. Cans that say do not drain contain only tuna or sometimes salmon. They only have natural occurring fish oils and juices and those are rich in omega threes.
Canned tuna is the only seafood in some people's diets. So that's why mercury contamination is such a concern in this particular fish. Mercury is a known neurotoxin. Too much of it is harmful to children, whose bodies and brains are still growing.
Often, you'll need to take chelators (medicine that removes metal from your body) for several weeks to months after mercury exposure to completely remove the chemical from your body.
High exposure to inorganic mercury may result in damage to the gastrointestinal tract, the nervous system, and the kidneys. Both inorganic and organic mercury are absorbed through the gastrointestinal tract and affect other systems through this route.