Can you eat tuna while pregnant? Tuna Fish has been a staple in the American diet since the 1910’s. , However recently, its use has been on a decline.

Ever wondered why?

Tuna is famous because it has very low levels of fat and very high levels of protein, minerals, vitamins and PUFAs. Unfortunately, it was found out that  it comes contaminated with pollutants such as heavy metals and their organic derivatives due to ocean pollution. Even contaminated tuna is considered to be an excellent source of protein and Vitamin D, B3, B6, B12, Magnesium, Phosphorous, Iodine and Potassium.

Can You Eat Tuna While Pregnant?

Pollutants such as heavy metals and their organic derivatives e.g. mercury, lead, arsenic, dioxins, polychlorinated biphenyls accumulate in fish as a result of ocean contamination. Fish contaminated with mercury is one of the major ways of exposure to mercury poisoning in America, especially through tuna consumption in kids and pregnant women. Mercury exposure can lead to adverse neurological and neurodevelopmental effects during fetal development due to maternal fish consumption in pregnancy.

Furthermore PUFAs also act as major components of the cell membranes and can lead to a positive effect on neurological advancement when consumed regularly. PUFAs especially DHA plays an important role in fetal brain and retina development when consumed by pregnant mothers. In adults PUFAs are especially important during maturation and ageing, as it is believed people who regularly consume PUFAs have sharper reflexes even in old age.

In the same way Omega-3 fatty acids are not only involved in better heart health but they are also implicated in reducing risks of cancer. Studies concerning colon cancers have clearly shown Omega-3’s from tuna can lower risk of colon cancer.

The bigger the tuna fish is in size the more Omega 3 fatty acids it has generated in its body, however at the same time the fish has had more time to accumulate toxic mercury in its body due to sea pollution. Mercury is mounted up in the muscle tissues of the tuna fish.

For example canned Albacore tuna is found to contain more PUFAs but since the Albacore is a relatively large fish it can also have increased levels of mercury. Whereas chunk light contains lower quantities of both mercury and PUFAs, making the PUFAs and mercury levels in tuna a controversial relationship. The FDA states 4 ounces of canned tuna have about 40 micrograms of mercury.

Pregnant women are especially recommended tuna according to their weight. For example the NRDC stipulates a pregnant woman weighing 100 lbs. should not consume more than 1 can of White Albacore tuna in canned from meanwhile, but 1 can of chunk light tuna can be consumed every 6 days. Similarly a woman with a weight of 20 lbs. should only consume 1 serving of White Albacore tuna over a period of 10 weeks.

Mercury released from burning of fossil fuels in factories and power plants assimilates in lakes, rivers, and oceans, from where it is absorbed or ingested by small organisms such as fish. For a fish as big as tuna the mercury levels are increased in their bodies. Mercury cannot be seen or tasted in fish and cooking does not diminish its concentration.

Is Tuna Healthy? 

Tuna is a well-established source of PUFAs or omega-3 fatty acids. According to the FDA 4 ounces of canned tuna probably contains 1,000 milligrams of EPA i.e. Eicosapentaenoic acid and DHA i.e. Docosahexaenoic acid, both of which are categorised as Poly unsaturated fatty acids (PUFAs).

PUFAs are one of the only established nutrients to have a positive effect on the health due to their anti-inflammatory properties and are especially beneficial for the human heart. Other protective effects of regularly consuming tuna include lower risk of diabetes and stroke. Consumption of omega-3 fatty acids from tuna can helps regulate blood pressure and lowers the risk of ‘clogging’ in the blood vessels. Some studies specially highlight the cardiovascular benefits of eating tuna for lowering the risk of Atrial Fibrillation, a condition which refers to irregular electrical impulses in the heart. Three or more serving of tuna every week is linked to 15-30% decreased risk of developing Atrial Fibrillation.

Canned tuna is the most commonly consumed form of seafood in America and is essentially a meat alternative. It is most popularly used to make tuna salads, tuna sandwiches or tuna casseroles. The USDA Foods specifies that tuna can be eaten with vegetables, mustard, mayonnaise, whole grain breads or crackers to attain maximum taste. Tuna in cans is preserved in edible oils, brine, salted water or various sauces, and is mostly either ‘chunked’ or ‘flaked’ after processing.  In the US, 52% of canned tuna is used for tuna sandwiches, while 22% is used in for easy tuna salads and 15% of canned tuna goes into making tuna casseroles.

In 2014, about 67% of the canned seafood sold in the US was canned tuna. However, these numbers have gone down from 3.9 pounds/person back in 1989, to 2.3 pounds/person. The fall of the canned tuna is a classic tale of how the American public is improving their relationship with their diet due to increased health awareness. Tuna fell from favour in the 1980’s when it was found to contain major pollutants which cause adverse effects. In addition the tuna-catching practice which results in killing dolphins also resonated with the American public, leading to a boycott of some major tuna producing brands.

Recently, research has shown different types of tuna contains high quantities of selenium and PUFAs i.e. Omega-3 fatty acids which can have a positive effect on the health. However at the same time tuna is one of the few fish with very high levels of mercury, making the consumption of tuna a controversial debate. Many health experts are still undecided if the benefits of tuna nutrition are higher than the negative effects, since mercury poisoning can lead to elevated risks of cardiovascular problems and slowing down of neurological development.

Bio-Accessibility Of Selenium

The bio-accessibility i.e. availability or absorption of Selenium (Se) in the body, is seen to be very high in tuna. Selenium is present in higher concentrations in raw and cooked tuna than in canned tuna. Selenium bio-accessibility means it is readily available to the body and completes the daily requirement of Se, which is 160 g per week. The mineral Se is present in tuna in an unusual form also known as selenoneine which serves as an antioxidant protecting the red blood cells from free radical damage in the fish.

In recent years Selenium’s presence in tuna fish has gained prominence, since it binds with mercury (methyl mercury MeHg—a neurotoxin) inside the body of the tuna fish. The binding of Se with MeHg leads to the formation of the complex Se:MeHg which results in a lower risk of mercury poisoning when humans eat tuna. A 4-ounce serving of tuna is believed to contain approximately 2-3 milligrams of selenoneine and when we eat tuna the antioxidant property of Se is transferred to our body.

Some researchers believe eating tuna even when it is contaminated with mercury poses lower risk of mercury poisoning if the tuna has a higher content of Se. Studies of tuna claim even the best canned tuna contains low quantities of both Mercury and Selenium.

Tuna Canning

On the other hand the canning of tuna involves a process in which the entire tuna fish is steamed for hours, as a result of which the tuna releases a watery liquid also known as cooking juice. The juice is discarded by the tuna manufacturers however researchers believe it contains very strong antioxidants. When the nutritional composition of the cooking juice was examined it was found to contain small protein fragments called peptides, which have strong antioxidant properties.

The cooking juice is capable of protecting the cell membranes from lipid peroxidation i.e. oxygen-related damage. It is possible cooking tuna at home will preserve more of its juice resulting in retaining more of its beneficial antioxidant peptides.

A study found that cooking juice obtained from tuna contains very high levels of DPPH (1,1-diphenyl-2-picrylhydrazyl) which is a powerful scavenging agent i.e. prevents free radicals from damaging tissues in the human body. The peptide sequence found in tuna comprised of four to eight different amino acid residues. Therefore it is recommended that tuna should not be consumed in highly processed varieties and home cooking methods are preferred by some nutrition experts.

Scombroid Poisoning

The US Food Allergen Labeling and Consumer Protection Act (FALCPA) states fish is number four on the classification of allergens in America. About 2-3% of US adults have developed allergies to consuming fish. In tuna fish allergy is mainly caused by a type of food poisoning called scombroid poisoning, which is also referred to as histamine poisoning.

Some tuna species contain very substantial amounts of the amino acid histidine. When tuna is canned interactions with certain bacteria can cause the histidine to convert into histamine, which causes allergies. Histamine is present in high amounts in canned tuna that has undergone excessive processing, as bacterial levels rise when certain bacteria interacts with each other for a long period of time usually when food has been stored for a long time. A 4 ounce serving of canned tuna is expected to contain about 20-240 milligrams of histamine.

The scombroid fish poisoning from tuna is usually experienced within hours and its symptoms include flushing, sweating, nausea and vomiting and headache.

Dietary Recommendation

Although tuna fish contains mercury but the benefits of tuna are believed to surpass its negative effects if eaten with caution and within the recommended limit. The EPA and FDA have recommended eating not more than 8 to 12 ounces or 3 to 4 servings of a variety of fish including tuna, especially tuna with lower levels of mercury.

There are different species of tuna available in the US market and the Natural Resource Defence Council (NRDC) has listed all of the species of tuna which contain very high levels of mercury. The NRDC recommends the canned tuna from Chunk light and Skipjack contain moderate levels of mercury and only six or less of their serving should be eaten every month.

Meanwhile the Canned  Albacore tuna and Yellow-fin tuna species contain high levels of mercury and consumption of only three or less servings are recommended very month.  The tuna species Bigeye and Ahi are not recommended for eating since they contain very high levels of mercury. The recommendations were developed by the NRDC in association with the USDA.

Simple Tuna Sandwich

One of the reasons why tuna is such a big part of the American diet is the ease with which it can be prepared, since tuna as a meat alternative can be simply applied on toasts and eaten with ease. For example a simple tuna sandwich requires one can of tuna without cooking or any sort of preparation, with choice of sliced vegetables e.g. celery, onions, cucumbers, capsicum, tomatoes etc. and choice of bread slices e.g. brown, bran, white etc. A simple tuna salad sandwich made with 5 ounces of Tuna Salad and 3 ounces of Bread contains only 679 calories.