Why You Should Avoid Eating Canned Tuna Every Day

Canned tuna might not be the sexiest food in the world. Still, it's a relatively economical and convenient choice if you're looking for a protein-heavy and shelf-stable snack, salad topping, recipe ingredient, or sandwich filler. However, you probably want to limit how many times a week you eat canned tuna. Despite the nutrient density and weight management superpowers of tuna, it contains methylmercury, a naturally occurring toxic compound linked to serious health problems in children and adults. As a result, eating canned (or pouch-based) tuna every day could put your health at risk due to a toxic buildup of methylmercury in your system.

Though you could encounter forms of mercury through other means, the United States Environmental Protection Agency (EPA) explains that eating fish such as tuna is one of the primary ways individuals are exposed to methylmercury. Essentially, when you eat tuna, you consume any methylmercury that has amassed in the fish's body. The EPA says that, given how much methylmercury circulates around the Earth, the majority of people have some methylmercury inside them. Once there, the human system slowly removes methylmercury over a span of months, according to Healthline. Yet, you wouldn't want to let your methylmercury levels get too high because they may start to affect you neurologically and in other ways.

What side effects can ingesting large quantities of methylmercury cause adults and children? A 2012 study published in the Journal of Preventive Medicine & Public Health explored the outcome of methylmercury overexposure and its related toxicity. It found that among people living in communities that ate high quantities of methylmercury-containing fish, incidences of memory problems, speech disorders, and concentration difficulties were notably common.

Another Environmental Health study from 2003 corroborates the idea that methylmercury can harm the human body and brain. As part of the study, researchers collected hair samples from 129 adult participants. Those whose hair exhibited exposure to methylmercury had notable "detectable alterations in performance on tests of fine motor speed and dexterity," among other symptoms.

Symptoms of methylmercury aren't just limited to the person who's been exposed. In a 2005 meta-analysis found in the American Journal of Preventive Medicine, researchers concluded that women who ate a lot of methylmercury when pregnant could pass it on to their fetuses. This process, according to the meta-analysis, could then put the babies at risk for cognitive disorders.

You don't have to remove canned tuna from your budget-friendly healthy shopping list. However, you may want to get choosier about the type of canned tuna you buy, as well as reduce the amount of times you eat it per week. In general, cans labeled "white tuna" contain more methylmercury than "light tuna." White tuna typically comes from larger tuna varieties, whereas light tuna hails from their smaller counterparts. Since larger tuna have more body mass, they take in more methylmercury over time because of their size. Consequently, swapping white tuna for light tuna may be one way to lower your possible exposure to methylmercury.

Just how much better could light tuna be for you than white tuna? A 2004 study in the journal Environmental Research examined several brands of canned tuna. After their analysis of 168 cans, the researchers discovered that light (and chunk light) canned tuna contained a mean of 0.118 ppm of methylmercury. In contrast, white canned tuna had a mean of 0.407 ppm of methylmercury, more than twice as much.

Canned tuna isn't a terrible ingredient for you or your children. It's a solid superfood that's great if you want to stay fit and fuel your muscles. As the U.S. Department of Agriculture notes, 3 ounces of tuna will cost you less than 100 calories, delivers an impressive 21.7 grams of protein, and offers up calcium, vitamin A, and other nutrients. Oh, and it doesn't contain any sugar, which is a nice perk. Tuna is also well-respected for its omega-3 fatty acid content. Healthline reports that an ounce of fresh canned tuna gives you 25 mg of DHA and 3 mg of EPA omega-3 fatty acids. Both types of fatty acids are thought to provide supportive benefits for your cognitive abilities, as well as your eye and heart health.

The key to canned tuna is to keep its methylmercury connection in mind when planning out your weekly meals. The FDA recommends indulging in a serving of canned tuna up to three times a week, as long as it's the light type. If you're pregnant, trying to become pregnant, or breastfeeding, consider talking with your healthcare provider about whether or not you should give up canned tuna temporarily. Just don't toss your canned tuna unnecessarily because it can still be a fine pick for your pantry. If you really want to eat fish every day, take advice from MedicineNet, which gives a thumbs-up to salmon, shellfish, and sardines as low-mercury options.