Is Canned Tuna Bad For You?

Tuna is a saltwater fish of the mackerel family. The Atlantic Bluefin Tuna can weigh up to 1,508 lbs. and be up to fifteen feet long. These fish are found in warm seas and fished commercially to provide the canned and fresh tuna around the world. Tuna is also a popular game fish. It was first canned in production in Australia in 1903. Typically canned in oils or water, it can also be canned with a variety of sauces for flavor. The tuna fish is usually processed to be “chunked” or flaked and stores well. The fish is processed after being gutted and pre-cooked from 45 minutes to three hours. Next, it goes through the process of being cleaned, filleted, and sealed. The final process involves the can being heated for two to four hours to kill any remaining bacteria.

Tuna is a healthy lean protein, which promotes strong muscle tissue, immune health and cell development. This popular saltwater fish also contains high levels of Omega-3 fatty acids (oils), docosahexaenoic (DHA) and eicosapentaenoic (EPA) that help improve cardiovascular health, by strengthening blood vessels and lower blood pressure. Some of the commercial processing methods can destroy many of the omega-3 oils, so the actual levels per can may vary.

Additionally, tuna is a source of niacin, a B-vitamin that has shown to help regulate cholesterol by preserving the high-density lipoprotein (HDL) levels. Tuna also possesses potassium, which is required for good heart, kidney and liver function and selenium; which is used by the body for reproductive health, DNA mechanics and thyroid function. However, canned tuna in water contains 520 milligrams of sodium (salt). With the daily recommended amount being 2,300 milligrams, one can of tuna in water consumes a significant amount your daily salt allowance. High sodium affects the body’s circulatory system causing hypertension and cardiovascular disease. Large doses of sodium can increase dehydration, cause water retention, and cause swelling in the extremities (edema).

The content of Mercury in tuna can vary greatly between brands. A study conducted by Rutgers University found that Star-Kist tuna contained ten times more mercury than any other canned tuna brand. The mercury levels in tuna can also vary by the specific breed of tuna fish, as well. Larger fish, such as Ahi and Bigeye tuna, typically have higher Mercury levels than smaller breeds. Due to the mercury content, pregnant women should try to avoid their consumption of tuna. Mercury can cause great harm the neurological and brain development of the baby. The Food and Drug Administration (FDA) guidelines pertaining to canned tuna suggest that special populations, including pregnant women, nursing mothers, and children, limit their tuna intake to one 6-ounce serving per week. If the tuna is “light chunk," the serving size moves up to 12-ounces. However, since it is impossible to determine how much Mercury is in a particular serving, it is better to avoid it all together.  

There is an ongoing battle over the health of non-child bearing adults’ consumption of Mercury. On one hand, you have the great values of high protein, Omega-3 oils (though some are lost in processing), and the convenience of tossing a can of tuna in your bag for lunch. On the other hand, you have the risks surrounding Mercury poisoning. There is no set amount of Mercury established that is equivocal to Mercury poisoning. There are too many variables to consider, such as the type of fish, the brand, what is actually in the can (as levels vary from can to can, even within brands), and the specifications of the individual consuming it. When this heavy metal poisoning occurs, it largely affects the neurological system.  A Harvard studied found that canned tuna accounts for over one-third of the average American’s exposure to Mercury.

Much like all foods sold in a can, tuna cans also bleed bisphenol-A (BPA) into the food. BPA is a plastic(s) processing chemical that induces deceitful hormone reactions in the human body’s endocrine system and is linked to a host of other problems such as a compromised immune system, obesity, diabetes, cancer, female reproductive problems, hyperactivity in children and much more. These reactions are especially dangerous for babies, children, and young adults, but pose some risk to humans in every age bracket. The use of BPA as a can liner has come under great scrutiny in recent years, so much so that some food processing plants have stopped using it. However, in many cases, BPA has been replaced by bisphenol-S (BPS). Bisphenol-S also interferes with the hormones in the body. Moreover, tuna sold in a pouch also comes with similar risks. The primary reason packaging plants switched to pouches over cans is that pouches occupy less space.

Another thing to take into consideration is whether you want your tuna in oil or water. Canned tuna in oil has a richer flavor and a smoother texture. However, meat packaged in oil poses a greater risk to overall health than that of meat packed in water. The additional oil increases the fat content. The tuna in water has a lighter taste and the benefits you receive are well worth it.

There has been a big trend in some dieters, athletes, and weight lifters towards consuming tuna for at least one meal a day, or even multiple meals each day. Its high protein levels and low calories help these populations meet their goals quickly. The question continues cycle: How much canned tuna is too much? There is not a definite answer. It is likely not healthy to eat more than one can per day and probably best to limit yourself on how many days in a row you consume it. If you do consume it daily, be aware of what breed of tuna you are eating and steer clear of the big fish. It is better to aim for light chunk tuna, though there is still no guarantee of the level of Mercury. Remember too much of a good thing can be a bad thing. As with everything—moderation is the key!