Is canned tuna healthy?Pawel Malczewski
Canned tuna is one of the most nutritious foods available.
However, besides a wide variety of nutrients, it also contains various toxins such as methylmercury, BPA and histamine, which can be detrimental to one’s health.
This article discusses how to balance the health benefits of canned tuna against the potential danger of toxicity. At what point do the negative effects outweigh the health benefits? For a quick answer click here.
Canned tuna is a popular food worldwide. It is used, for instance, on top of salads or as part of an afternoon snack.
On the one hand, canned tuna seems like a healthy food choice, due to its many essential nutrients and its beneficial effects on normal physiology, optimal fetal neural development, and general health in pregnancy.
On the other hand, canned tuna contains methylmercury and other heavy metals, from polluted waters, chemicals, the lining of the cans, and histamine, from inappropriate handling of fish. (1)Kim Se-Kwon. Seafood Science: Advances in Chemistry, Technology and Applications. CRC Press. 1 edition (September 16, 2014). Available here.
People often underestimate the dangers of these chemicals and metals, but consuming too much canned tuna may lead to some serious health problems.
The nutritional and toxic contents of canned tuna, and, therefore, the potential positive and negative health effects of consuming it, differ depending on the:
- Tuna variety
- Tin content besides the fish component, such as vegetable oil versus spring water
- Material used for lining the cans
- Method of storage after the tuna is caught
For instance, the fat content varies between 3% and 33%, canned tuna in water contains more omega 3 fatty acids than tuna in oil. Light tuna has less mercury than albacore tuna. In addition, various brands produce different quality products.
There is an optimal amount of canned tuna that you can eat per week. This will enable you to get the most health benefits but at the same time won’t reach the maximum safe level of methylmercury, which is the most abundant, illness causing toxin in canned tuna.
The following sections describe the “good and bad” aspects of eating canned tuna and a summary of how much canned tuna you can eat per week and which type to pick. The calculation is based on upper safe limit recommendations of methylmercury. (2)Maqbool A, Strandvik B, Stallings VA. The skinny on tuna fat: health implications. Public Health Nutr. 2011 Nov;14(11):2049-54. Available here.
What types of tuna do we usually eat?
The most common type of fresh tuna available in stores comes from large and older fish varieties such as Bluefin tuna.
Canned tuna is usually found in two varieties, a small tuna variety called “light tuna” (mainly skipjack tuna) and a large tuna variety called “white tuna” (albacore tuna). Albacore tuna has the highest methylmercury content of all canned fish, but at the same time it is richer in omega 3 fatty acids DHA and EPA.
When is canned tuna good for you?
There are many health benefits of tuna, due to its high nutrient contents. Canned tuna is an excellent source of many nutrients such as protein, fat, Omega 3 fatty acids, vitamin A, vitamin B group (B1, B2, B3, B5, B6, B12), phosphorus and selenium and a good source of copper and magnesium (read more..). Many of these nutrients have significant positive effects on our health.
Health benefits of canned tuna
- Tuna may have anti-inflammatory properties, due to high omega 3 (EPA and DHA) and selenium contents. EPA and DHA fatty acids regulate the inflammatory system and prevent excessive inflammation.
NOTE: tuna canned in water has more omega 3 fatty acids than tuna canned in oil.
- The omega 3 and selenium contents may also decrease the risk of cardiovascular related diseases. (3)Long chain omega-3 fatty acids and cardiovascular disease: a systematic review. Available here.
- Selenoneine is a selenium containing compound found in the tissues and blood of tuna. It has strong antioxidant properties. Selenoneine protects heme proteins from iron oxidation by binding to hemoglobin and myoglobin. It also reacts to methylmercury, the major contaminant in tuna, reducing the danger of mercury toxicity. (4)Ganther HE, Goudie C, Sunde ML, Kopecky MJ, Wagner P. Selenium: relation to decreased toxicity of methylmercury added to diets containing tuna. Science. 1972 Mar 10;175(4026):1122-4. Available here.
Consuming selenoneine rich tuna lowers the reactive oxygen radicals’ levels, and reduces the risk of cancer formation, and of developing various chronic diseases. It also slows the effects of aging. (5)Yamashita Y, Yabu T, Yamashita M. Discovery of the strong antioxidant selenoneine in tuna and selenium redox metabolism. World J Biol Chem. 2010 May 26;1(5):144-50. Available here.
- Tuna canned in water contain antioxidant peptides that are released during cooking. These peptides may protect the cell membranes from damage due to peroxidation, an oxygen-related damage. (6)Hsua KC, Lub GH, Jao CL. Antioxidative properties of peptides prepared from tuna cooking juice hydrolysates with orientase (Bacillus subtilis). Food research international. Volume 42, Issues 5–6, June–July 2009, Pages 647–652. Available here.
Why canned tuna can be bad for you?
- Methylmercury in tuna
Methylmercury is an extremely poisonous form of mercury formed in water, soil, or plants as a result of reaction between bacteria and mercury.
All tuna is contaminated with methylmercury to some degree. The important questions are:
- which canned tuna products contain, on average, the least amount of mercury? Light tuna.
- how much canned tuna can we eat weekly not to exceed the recommended upper safe limit of mercury?
It depends on the body weight – see table below.
- how else we can avoid crossing that upper safe limit?
Don’t eat only tuna, consume other types of fish with lower amounts of mercury, such as sardines or salmon.
- who is in the risk group and should lower the consumption of tuna?
Pregnant and breastfeeding women and young children.
The following table contains a summary of the safe weekly limits of cans of snack-size tuna per body weight. The data was taken from the FDA which gathered the main results from major studies that used a large sample of products.
For more details, and very important information on mercury in fish, see the article “how much canned tuna is safe”.
As an example, a 70 kg/154lb woman shouldn’t eat more than about 7 cans of snack size canned light (skipjack) tuna per week and no more than 2.5 cans of white (albacore) tuna.
- Other heavy metals
In addition to mercury, other potentially harmful heavy metals are also found in tuna. However, these metals are found to be in acceptable quantities: lead (Pb), cadmium (Cd), Nickel (Ni) (7)Ashraf W, Seddigi Z, Abulkibash A, Khalid M. Levels of selected metals in canned fish consumed in Kingdom of Saudi Arabia. Environ Monit Assess. 2006 Jun;117(1-3):271-9. Available here.
- Bisphenol A and alternatives
A chemical called bisphenol A (BPA) has been used in the can lining to protect the food from direct contact with the metal surface.
It is now prohibited in many countries due to its hormone-like properties and interference with the endocrine system, causing serious health complications.
Many substitute chemicals have been used as alternatives, such as bisphenol B (BPB), bisphenol E (BPE), bisphenol F (BPF), bisphenol S (BPS) and 4-cumylphenol (HPP), but the safety of these chemicals has not been thoroughly researched. Some studies show that these chemicals have similar endocrine-disruptive properties to BPA, although the mechanism may be different. (8)Héliès-Toussainta C, Peyrec L, Costanzoa C, Chagnond MC, Rahmanic R. Is bisphenol S a safe substitute for bisphenol A in terms of metabolic function? An in vitro study. Toxicology and Applied Pharmacology. Volume 280, Issue 2, 15 October 2014, Pages 224–235. Available here. (9)Rosenmai AK, Dybdah M, Pedersen P, van Vugt-Lussenburg BM, Wedebye EB, Taxvig C, et al. Are Structural Analogues to Bisphenol A Safe Alternatives? Toxicol. Sci. (May 2014) 139 (1): 35-47. Available here.Although these chemicals are used in amounts that comply with the safety regulations, to insure the least exposure to these toxins, it is advisable to choose fresh products rather than canned.
Tuna meat contains varied levels of histamine. Histamine levels in tuna of above 200ppm (parts per million) may cause poisoning.
Most countries have established either 50ppm or 100ppm as a safe limit.
Histamine levels in tuna increase rapidly with time and inadequate temperature. To prevent unacceptable levels, tuna must be chilled on the fishing vessel to below 4 degrees Celsius (39.2 Fahrenheit) immediately after catching and be transported in chilled trucks.
In the most developed countries, the usual levels of histamine in tuna vary between 1ppm and 30ppm, since quality procedures are very strict. However, unacceptable levels of histamine (above 200ppm or even 500ppm) may occur in tuna fish caught in small, developing countries, especially in the tropics, due to inadequate chilling facilities on the fishing boats and in the transport trucks.
Canning or cooking the tuna does not reduce the histamine levels, so if it was badly handled, the excessive amount of histamine will remain the same.
Histamine poisoning symptoms, such as headache, burning or tingling sensation in the mouth, skin rash, inflammation or reduced blood pressure, may develop between 10 minutes to 2 hours after consumption. It normally subsides within 24 hours, except in the cases of elderly or sick individuals, who may need hospitalization. (10)Atuna. Histamine (scombrotoxin). Available here.
To avoid histamine poisoning, chose canned products from trusted brands.
- Canned tuna in oil
Canned tuna in oil is not a good choice for a few reasons.
Firstly, the oil used is usually vegetable oil, which is highly processed involving toxic chemicals and contains a high proportion of inflammation-causing fatty acids such as omega 6.
Another reason is that canned tuna in oil has lower amounts of omega 3 fatty acids than canned tuna in water.
In addition, if the olive oil used for canning is not extra virgin, it is usually of inferior quality.
- Can you eat canned tuna when pregnant?
Despite the fact that the consumption of fish is beneficial for a developing fetus, breast-fed infants and young children, the intake of canned tuna and other fish high in mercury should be limited.
There are certain types of fish, such as tilefish, swordfish, shark or kink mackerel, that must be avoided when women are pregnant or breastfeeding, due to the excessive amount of mercury. Although Albacore tuna is high in mercury compared to the other canned tuna products, it still contains much less mercury than the above mentioned fish. (read more..)The official recommendation for pregnant and breastfeeding women is 6 oz. (about 170g) per week of albacore tuna. Since light tuna has only 30% of the mercury compared to albacore tuna, it is safer for pregnant, breastfeeding women and young children to choose the light tuna variety, especially in water or brine, for higher omega 3 fatty acids contents. Since the methylmercury contents in light tuna are lower, the weekly limit can be higher. (11)FDA. U.S. Food and Drug Administration. Fish: What Pregnant Women and Parents Should Know. Available here.
NOTE: it is important to note, however, that in order to minimize any risk, rather than eating tuna or other fish with high mercury levels, it is safer to choose fish that are low in mercury. This includes sardines or salmon, which still contain high amounts of EPA and DHA for the neuro-development of the fetus and infants.
How much canned tuna is safe?
Although other toxins contained in the canned tuna are important to consider, the main risk of having canned tuna fish comes from the methylmercury contents.
The summarized information on the weekly safe limits is in the above section on methylmercury and the detailed information is in the article “How much canned tuna is safe to eat?”.
Canned tuna can be a healthy meal if consumed within the safe limits. These limits are mainly determined by the methylmercury contents, which is the most significant toxin contained in tuna flesh.
Insuring that the overall weekly methylmercury consumption from all food sources and the outside environment is kept under the safe limit, canned tuna can be a healthy addition to the diet.
Which canned tuna is healthiest?
The healthiest canned tuna is:
- light tuna – for minimum mercury content;
- water packed – contains more omega 3 fatty acids than in oil;
- packed raw and heated – to preserve most nutrients and taste;
- Purchased from trusted brands.
- Alternate canned tuna with other nutrient rich fish, such as sardines and salmon.
- Use more fresh fish rather than canned ones;
- Limit canned tuna consumption to the above weekly limit;
- Be aware of other mercury containing products to reduce your daily exposure.
References [ + ]
|1.||↑||Kim Se-Kwon. Seafood Science: Advances in Chemistry, Technology and Applications. CRC Press. 1 edition (September 16, 2014). Available here.|
|2.||↑||Maqbool A, Strandvik B, Stallings VA. The skinny on tuna fat: health implications. Public Health Nutr. 2011 Nov;14(11):2049-54. Available here.|
|3.||↑||Long chain omega-3 fatty acids and cardiovascular disease: a systematic review. Available here.|
|4.||↑||Ganther HE, Goudie C, Sunde ML, Kopecky MJ, Wagner P. Selenium: relation to decreased toxicity of methylmercury added to diets containing tuna. Science. 1972 Mar 10;175(4026):1122-4. Available here.|
|5.||↑||Yamashita Y, Yabu T, Yamashita M. Discovery of the strong antioxidant selenoneine in tuna and selenium redox metabolism. World J Biol Chem. 2010 May 26;1(5):144-50. Available here.|
|6.||↑||Hsua KC, Lub GH, Jao CL. Antioxidative properties of peptides prepared from tuna cooking juice hydrolysates with orientase (Bacillus subtilis). Food research international. Volume 42, Issues 5–6, June–July 2009, Pages 647–652. Available here.|
|7.||↑||Ashraf W, Seddigi Z, Abulkibash A, Khalid M. Levels of selected metals in canned fish consumed in Kingdom of Saudi Arabia. Environ Monit Assess. 2006 Jun;117(1-3):271-9. Available here.|
|8.||↑||Héliès-Toussainta C, Peyrec L, Costanzoa C, Chagnond MC, Rahmanic R. Is bisphenol S a safe substitute for bisphenol A in terms of metabolic function? An in vitro study. Toxicology and Applied Pharmacology. Volume 280, Issue 2, 15 October 2014, Pages 224–235. Available here.|
|9.||↑||Rosenmai AK, Dybdah M, Pedersen P, van Vugt-Lussenburg BM, Wedebye EB, Taxvig C, et al. Are Structural Analogues to Bisphenol A Safe Alternatives? Toxicol. Sci. (May 2014) 139 (1): 35-47. Available here.|
|10.||↑||Atuna. Histamine (scombrotoxin). Available here.|
|11.||↑||FDA. U.S. Food and Drug Administration. Fish: What Pregnant Women and Parents Should Know. Available here.|