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Tuna is one of the healthiest foods out there. It is an incredibly rich source of protein while containing an insignificant amount of fat, making it a very useful food for weight loss.

However, recently there has been a lot of concern over the amount of mercury found in tuna and the adverse effects it has on the people eating it. So, the question remains, should you eat tuna? In short, yes, you should, but only a certain type, and only if you are not at risk for mercury poisoning. First, let’s take a look at the controversy surrounding tuna.

Is Tuna Toxic?

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Most people have heard by now that they shouldn’t eat too much tuna due to the amount of mercury that they contain. Well, that information is partially right, except for one small detail: most mercury that enters the ocean isn’t actually harmful, it’s the conversion of mercury into methylmercury that makes the consumption of tuna possibly dangerous.

Methylmercury is a highly toxic form of mercury that scientists believe is converted from mercury by some species of bacteria that live on the ocean floor. Methylmercury can be found in most forms of marine life, and often tend to build up in large predatory fish, such as tuna, as they eat prey that contain methylmercury. This concept is reflected in a study that measured mercury levels in different sized species of tuna.

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The study collected over 100 different tuna samples from 54 sushi restaurants and 15 grocery stores. Researchers used DNA testing to identify which species of tuna each sample belonged to. They found that mercury levels were highest in bigeye and bluefin tuna, two of the biggest tuna species, and that the lowest levels were found in skipjack tuna, one of the smallest tuna species. Although there are many other factors which effect a tuna’s mercury content, the general rule is the bigger the tuna is, the more mercury is in them.

How to Choose Canned Tuna

Like I mentioned before, the smaller a tuna is, the less mercury it is going to have in it. But the way tuna is harvested and the location that it grows up in also play an important role in their mercury levels. Also, even though you now know which species of tuna to look for, labels on canned tuna can make it fairly confusing to determine what you should eat to avoid mercury. Here is a breakdown of the most and least toxic forms of canned tuna.

  • Chunk White. Chunk white is the name that canned tuna producers use to label albacore tuna. Albacore is one of the healthiest fish you can eat, as long as it is caught in the U.S. or British Columbia. Although albacore isn’t necessarily the smallest species of tuna, they are usually caught when they are young, ensuring that they didn’t have enough time to build up high mercury levels.
  • Canned Light. The most common type of tuna that is marketed as “canned light” is usually skipjack tuna, which, as we discussed before, is one of the smallest species of tuna, therefor having much lower levels of mercury than other, bigger species. However, many studies have shown that this type of canned tuna still has levels of mercury that would be considered dangerous if eaten by women and children.
  • Chunk Light. Chunk light is a blend of a variety of different tuna species. It can often contain meat from small, low-mercury species such as skipjack, but can also contain meat from large, high-mercury species such as bigeye, making it best to avoid this type of canned tuna.

Who Should Eat Tuna

Nicoise tuna salad with salad greens, tomato, olives and flaked fresh tuna served on an omelette base, overhead view

Despite the real risks of overeating high-mercury fish such as tuna, most people can still consume a diet consisting of regular tuna consumption without having any adverse effects. However, there are certain demographics that are more at risk for mercury poisoning than others.

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According to information based on findings from the U.S. Environmental Protection Agency, a child weighing approximately 48 pounds that eats more than 1.4 ounces of tuna a week (that’s about one third of a can) can be at risk of brain damage due to mercury exposure. The same guidelines also stated that a woman weighing around 140 pounds would exceed their acceptable mercury exposure by eating more than 4.5 ounces of tuna a week. It is also advised that women who are pregnant avoid tuna or any other mercury-containing foods completely.

Mercury poisoning can effect many parts of the body. The most notable effect it has is on the brain but it can also have an impact on other organs such as the kidneys, lungs and skin. Symptoms of mercury poisoning include:

  • Red cheeks, fingers and toes
  • Bleeding from the mouth and ears
  • Rapid heartbeat
  • High blood pressure
  • Intense sweating
  • Loss of hair, teeth and nails
  • Blindness
  • Loss of hearing
  • Impaired memory
  • Lack of coordination
  • Abnormal speech patterns

If you are experiencing any of these symptoms and are consuming a diet high in mercury-laden foods, you may be suffering from mild mercury poisoning. Let us know if this information was useful for you in the comment section.

References:

http://www.whoi.edu/oceanus/feature/how-does-toxic-mercury-get-into-fish

http://nutritiondata.self.com/facts/finfish-and-shellfish-products/4146/2

http://www.atuna.com/index.php/en/tuna-info/tuna-species-guide#yellowfin

http://www.rodalesorganiclife.com/food/mercury-tuna

http://www.newsmax.com/Health/Health-News/tuna-mercury-risk/2015/05/19/id/645428/

Image Sources:

http://www.hydroquebec.com/sustainable-development/documentation-center/images/figure-1-7.gif

http://stockarch.com/files/13/09/nicoise_tuna_salad.jpg

http://foodnetwork.sndimg.com/content/dam/images/food/fullset/2015/4/7/0/fnd_canned-tuna-primer_s4x3.jpg.rend.snigalleryslide.jpeg

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