No single category of nutrient has been more clearly determined to have anti-inflammatory health benefits than omega-3 fatty acids, and tuna is equally well-established as an important food source of omega-3s. In an average 5-ounce can of tuna, you are likely to get about 7-28 milligrams of EPA (eicosapentaenoic acid) and 140-850 milligrams of DHA (docosahexaenoic acid). Both EPA and DHA are critical omega-3 fatty acids for proper regulation of the body's inflammatory system and prevention of excessive inflammation. Generally speaking, you're likely to get more omega-3s from canned albacore than from canned "light" tuna made from other species of tuna like skipjack (but also at times including yellowfin, tongol, or bigeye). But you are also likely to get more mercury from canned albacore as well because albacore are typically larger and older, having had more opportunity to accumulate mercury from contaminated ocean waters.
Researchers in the Department of Marine Science at Coastal Carolina University in Conway, South Carolina have recently taken a very interesting approach to this controversial trade-off between the beneficial, anti-inflammatory omega-3s found in fish and their undesirable contamination with mercury. These researchers reviewed nutritional studies on the anti-inflammatory benefits of omega-3s to arrive at a daily intake recommendation of 500 milligrams for EPA-plus-DHA (combined). Next, they estimated how many servings of fish would be required to meet this recommended level. In the case of canned albacore tuna, for example, they estimated that a person would need to consume 9 servings per month (with 7 ounces per serving) to provide an average daily amount of 500 milligrams of EPA-plus-DHA.
Using a similar type of logic, they then took the National Academy of Sciences (NAS) recommended safe dose level for mercury, calculated a safe daily intake level of mercury from fish of 6.8 micrograms and estimated how many daily fish servings a person could consume without going over this 6.8 microgram limit. In the case of canned albacore tuna, they determined that only 3 servings of canned albacore tuna could be eaten each month if a person wanted to stay below the 6.8 microgram daily limit for mercury. Based on this logic, they concluded that canned albacore tuna did not provide a good trade-off between omega-3s and mercury since a person would need 9 servings per month to meet the omega-3 recommendation, but would actually have to stop after 3 servings in order to stay below the mercury limit. In fact, these researchers did not find any type of tuna (not only canned albacore, but also canned light tuna and wild ahi tuna) that was able to meet the omega-3 recommendation without exceeding the mercury limit. They did find other fish, however, that provided the desired amount of omega-3s without going over the mercury limit. These other fish included salmon, trout, shrimp and tilapia.
While we admire the creativity and logic used by these researchers to evaluate the trade-off between omega-3s and mercury in fish, we take a somewhat different approach while using their same logic. Like these marine science researchers, we think it's important for individuals to minimize their food exposure to mercury, and we like the idea of staying below the NSA limit. However, we also believe there is no reason for a person to depend exclusively on fish for their omega-3s, nor do we believe that all of a person's omega-3s must be provided in the form of EPA and DHA.
Many foods can provide small amounts of omega-3s, and other forms of omega-3s (like alpha-linolenic acid, found in many plant foods) also help to provide us with anti-inflammatory benefits. For these reasons, we believe that individuals have the flexibility to enjoy tuna and other types of fish by focusing on their overall diet and making sure they get plenty of anti-inflammatory omega-3s from all of their foods combined, while still staying below the mercury limit in their overall diet. From a practical standpoint, this approach means including a variety of omega-3 foods in the overall diet, emphasizing fish that are lower in mercury contamination, and including higher mercury fish on a more limited basis. Wild-caught Alaskan salmon, for example, could be eaten during the same week as tuna to help avoid excessive mercury exposure while still reaping the anti-inflammatory benefits of omega-3s.
While small amounts of antioxidant nutrients like vitamin C, manganese, and zinc are provided by tuna, it is unusually rich in one particular antioxidant mineral, namely, selenium. This antioxidant is not only concentrated in tuna but is also present in an unusual form called selenoneine. Selenoneine is especially helpful to the tuna as a nutrient for protecting their red blood cells from free radical damage. Interestingly, it is also able to bind together with mercury compounds in the fish's body (including methylmercury, or MeHg) and lower their risk of mercury-related problems. Because there are approximately 2-3 milligrams of selenoneine in a 4-ounce serving of tuna, we are likely to get some of this same antioxidant protection whenever we eat tuna. Equally interesting, tuna may turn out to be a fish that - even when contaminated with mercury—might pose less of a mercury risk to humans than might otherwise be expected due to the presence of selenium in this special form of selenoneine.
When you steam or sear or broil fresh tuna at home, this cooking process may also result in some special antioxidant benefits. These benefits are related to the presence of small protein fragments—called peptides—that may get formed during the cooking process when proteins in the tuna get broken down. Recent studies have shown that some of the protein breakdown products in tuna have strong antioxidant properties, including the ability to protect cell membranes from oxygen-related damage (a process called lipid peroxidation).
When researchers study the overall benefits of omega-3 containing fish in a regular diet plan, they almost always find cardiovascular benefits to emerge at the top of the health benefit list. Researchers know, for example, that consumption of omega-3 fish can increase the presence of omega-3s in the membranes of red blood cells as well as cells along the blood vessel linings. This increased level of omega-3s in the circulatory system is associated with better regulation of blood pressure and lower risk of blood vessel "clogging." Approximately 2-3 servings of omega-3 fish per week over the course of 3-4 months has been shown to provide these cardiovascular benefits, and in some studies, tuna has specifically been shown to raise bloodstream levels of omega-3s as described above.
In this area of cardiovascular benefits, some studies have also shown tuna to be a potentially helpful food in lowering risk of a heart-related problem called atrial fibrillation (AF). AF is a condition involving irregular electrical impulses within the heart. Intake of three or more servings of tuna and/or oily fish (like sardines or salmon) per week has been associated with a 15-30% decreased risk of AF in some studies. The common link in these studies between tuna and oily fish might obviously involve the omega-3 fats provided by these fish. At the same time, however, both tuna and oily fish like salmon and sardines provide significant amounts of vitamin D (and rank in our top four WHFoods for vitamin D richness) and they also rank as our top three foods for vitamin B12. These areas of vitamin richness might also play an important role in potential cardiovascular benefits associated with tuna intake. Finally, not to be left out of potential cardiovascular benefits provided by tuna are its nutrient contributions in the mineral department that extend beyond its selenium richness. Tuna is a good source of both magnesium and potassium, and each of these minerals are important contributors to healthy blood flow and heart function, especially with respect to well-regulated blood pressure.
Health benefits from tuna may also exist in the area of cancer risk. Here the research is somewhat mixed, for several reasons. First, there is very little research specific to tuna. Most of the large-scale studies have looked at fish intake overall, or fatty versus nonfatty fish, rather than tuna per se. Second, not all researchers classify tuna in the same way. Some classify it as a fatty fish, yet other classify it as a white fish (and non-fatty). Part of the reason for this inconsistency involves widespread consumption of canned albacore tuna, which typically contains less than 3 grams of total fat per ounce. In the area of colon cancer, there is clear evidence that increased intake of omega-3 fats from fish as a group can lower risk of this cancer type. While this fish group has almost always contained tuna in large-scale research studies, we're not aware of studies in which tuna has not been analyzed independently as a unique fish for helping lower colon cancer risk. In the areas of prostate cancer and renal cancer, there is also some evidence of decreased risk from consumption of fish containing omega-3s, although the findings seem to be more mixed for these cancer types, with some studies failing to show decreased risk.
It's worth adding that despite the relative absence of evidence regarding specific intake of tuna and cancer risk, there is a large amount of research connecting decreased overall cancer risk with increased intake of omega-3 fatty acids in the overall diet.
From an overall nutritional standpoint, tuna is more diverse in its nutrient content than many people would suspect. It's an excellent source of vitamin B3 (niacin), vitamin B6 (pyridoxine), and vitamin B12 (cobalamin), as well as a good source of vitamin B1, vitamin B2, and choline. In combination, the result is a wide variety of B-complex vitamins all supplied in valuable amounts by tuna. Tuna is also a very good source of the mineral phosphorus and a good source of the minerals potassium, iodine, and magnesium. Of course, because of its muscle content, tuna is an excellent source of protein, providing two thirds of the Daily Value (DV) in one 4-ounce serving. In fact, tuna is our top protein source at WHFoods. This nutrient diversity in tuna would be expected to provide support for other body systems not mentioned above, including energy metabolism and blood sugar regulation.
The tuna family is a diverse family of fish. Some tuna are classified as "pelagic" fish that live relatively close the surface or in water columns that extend downward for several hundred meters at most. Others are classified as "midwater" fish that can be found at depths up to 600 meters. Tuna swim in most of the world's oceans. For example, there are six major stocks of albacore tuna, in the North Atlantic, South Atlantic, Indian Ocean, Mediterranean Sea, north Pacific and south Pacific.
This family of fish ranges widely in size. Some tuna—like bullet tuna—average about 1 foot in length. Other tuna—like Atlantic Bluefin—average over 6 feet in length and have been known to reach a size of 15 feet. Most tuna migrate over many miles of water (for example, some regularly cross the Atlantic or Pacific Oceans, over a distance of many thousand miles). While some smaller species of tuna live no longer than 3-5 years, it is not unusual for larger species like bluefin to live upwards of 20 years. All tuna belong to the scientific family called Scombridae, which also includes mackerel and bonito.
Among the most commercially popular of all tuna species are the following.
Albacore are a moderately sized and moderately long-lived species of tuna, with a common length of 3-4 feet, common weight of 15-45 lbs., and an average lifespan of 9-12 years. Albacore tuna can be labeled as "white meat" tuna when canned and has become a popular canned variety in the U.S.
While smaller and shorter-lived than bluefin (on average), bigeye are still considered a large and long-lived species of tuna, able to reach lengths of eight feet or more and often averaging five to six feet. Bigeye are sometimes sold under their Hawaiian name, "ahi." Along with yellowfin and bluefin, some bigeye are also used in sushi and sashimi and labeled referred to as "maguro."
Blackfin tuna belong to the yellowfin subgroup of tuna but have not become a commercially important species, unlike their yellowfin counterparts. Blackfin are relatively small in size, averaging between 1-3 feet in length and often 10-20 lbs.
Bluefin are the largest of the commercial tuna species and can reach weights exceeding 1,000 pounds and lengths of nearly 15 feet. It is also common for bluefin to have a lifespan of 20 years, and in some cases, nearly twice that long. Some bluefin swim from the Gulf of Mexico (where they are born) across the entire Atlantic Ocean, live along the European coast of the Atlantic, and then eventually swim back to the Gulf of Mexico to reproduce. When swimming, their top water speeds can reach 40-45 miles per hour.
Bluefin are a popular species of tuna in preparation of sushi and sashimi, where they are often referred to as "hon maguro." You can also find bluefin tuna being referred to as "toro" (tuna belly) when served as sushi. Due to their larger size and longevity, bluefin also average higher mercury concentrations than most other species of tuna.
Bluefin are also some of the most endangered tuna species. The International Union for Conservation of Nature (IUCN) in Cambridge, UK lists Southern bluefin as "critically endangered" and Atlantic Bluefin as "endangered."
Skipjack is the species of tuna that you are most likely to find in a can of "light" tuna. They're a relatively small species of tuna, often weighing between five to six pounds and averaging one to two feet in length. Skipjack are also shorter lived, with a lifespan of two to three years. This combination of lifestyle circumstances also tends to make skipjack a tuna species that is lower in mercury accumulation.
Skipjack is most often sold as canned light tuna and is the most common species found in tuna cans. It's also sold fresh or frozen.
When prepared for sushi, skipjack tuna is sometimes referred to as "bonito" or "katsuo," and skipjack tuna is often used similarly to yellowfin tuna in preparation of sashimi. Some segments of the sashimi market prefer skipjack and use it interchangeably with yellowfin tuna in grilled or fried preparations.
Tongol (also called longtail) has become a popular alternative species of tuna in the canned "light" tuna market. Unlike many of its fellow tuna, tongol are less migratory, seasonal, and found primarily in the Indian and Western Pacific oceans. Virtually all commercially available tongol come from the coastlines of Malaysia, Indonesia, Thailand, and Iran (where the Indian Ocean becomes the Arabian Sea). Tongol are relatively small in size, averaging approximately 10-12 pounds and ranging from 1-3 feet in length. The overall lifestyle and size of tongol also make them lower in mercury accumulation in the limited data that we have seen. Although most canned light tuna features skipjack as its primary species, it is not unusual to find "light" canned tuna that include tongol.
Yellowfin are moderate-to-large sized tuna, ranging widely in size from one to two feet to as large as five to six feet, and in some cases, even longer. Smaller yellowfin average 10-12 pounds in weight, but larger yellowfin will average much more, in the range of 40-60 pounds (and in some cases, even more). Yellowfin are relatively fast growing and have an average lifespan of four to eight years. Their variable size also makes them variable in mercury accumulation, but most of the data we have seen on yellowfin show their mercury concentrations to fall at the moderate level.
Other species of tuna include bullet tuna (Auxis rochei), dogtooth tuna (Gymnosarda unicolor), slender tuna (Allothunnus fallai), frigate tuna (Auxis thazard), and kawakawa (Euthynnus affinis).
The evolution of ocean fish shows the emergence of tuna to have occurred approximately 45 millions years ago—long before humans were around to go fishing for them! Tuna swim in all of the earth's oceans (except for oceans at the North and South Poles), including all parts of the Atlantic, Pacific, and Indian Oceans, as well as the Mediterranean Sea. There is evidence of Phoenician trap fisheries for tuna as early as 2000 BC.
For most of human history, fishing for tuna has been a small-scale regional and seasonal practice. The unique migratory patterns of tuna made small coastal fisheries for tuna the rule rather than the exception. Beginning in the 1940's and 1950's, however, industrial fishing for tuna started to become more and more widespread, with greatly expanded tonnage and offshore distances. Tuna—and particularly certain species, like bluefin—have been overfished on a global basis and Thailand, Ecuador, the Philippines, Spain, China, Mauritius, and Indonesia were the countries exporting the greatest volume of canned and processed tuna in 2014. Among species produced, skipjack led all other species, with yellowfin ranking second. Between 50-75 countries regularly participate in the commercial tuna production, most of which takes place in the Atlantic, Pacific, and Indian Oceans. In comparison to other fish, tuna has yet to be extensively farmed, even though there is increasing commercial investigation of tuna farming in various regions throughout the world, including the Mediterranean. The use of net pens in an open sea environment to contain and raise bluefin tuna has been experimented with in this region (along with other regions worldwide). However, few scientists believe that net pen farming can help to compensate long-term for overfishing of tuna, or alleviation of problems related to their endangered status.
Tuna is sold in many different forms. It is available fresh as steaks, fillets, or pieces. Tuna is probably best known in its canned form.
Just as with any seafood, it is best to purchase fresh tuna from a store that has a good reputation for having a frequent supply of fresh fish. Get to know a fishmonger (the person who sells the fish) at the store, so you can have a trusted resource from whom you can purchase your fish with confidence.
Fresh whole tuna should be displayed buried in ice, while fillets and steaks should be placed on top of the ice. Try to avoid purchasing tuna that has dry or brown spots.
Smell is a good indicator of freshness. Since a slightly "off" smell cannot be detected through plastic, if you have the option, purchase displayed fish as opposed to pieces that are prepackaged. Once the fishmonger wraps and hands you the fish that you have selected, smell it through the paper wrapping and return it if it has a truly strong fishy odor.
Canned tuna is available either solid or in chunks, and is packaged in oil, broth or water. Although the tuna packed in oil is usually the moistest, it also has the highest fat content, and the oils in which it is packed are high in omega-6 fats. Since omega-6s and omega-3s compete for the same enzymes that activate them for use in the body, and most Americans already consume too many omega-6 fats in comparison to omega-3s, it is best to purchase tuna packed in water or broth. Oftentimes, canned tunas do not distinguish which specific species was used except to note that it is either light tuna (bluefin or yellowfin) or white tuna (usually albacore).
One final note about tuna selection: at present, the U.S. Department of Agriculture National Organic Program has yet to implement organic certification standards for seafood, including tuna. In the absence of organic certification, you may want to obtain more additional information on salmon than you otherwise might do with certified organic foods, and for this reason, our Individual Concerns section provides you with links to additional websites that provide high-quality and straightforward information about seafood choices (including salmon).
When storing all types of fresh seafood, including tuna, it is important to keep them cold since fish spoils quickly and is very sensitive to temperature. Therefore, after purchasing tuna or other fish refrigerate it as soon as possible. If the fish is going to accompany you during a day full of errands, keep a cooler in the car where you can place your tuna to make sure it stays cold and does not spoil.
The temperature of most refrigerators is slightly warmer than ideal for storing fish. To ensure maximum freshness and quality, it is important to use special storage methods to create the optimal temperature for holding the fish. One of the easiest ways to do this is to place fish, which has been well wrapped, in a baking dish filled with ice. The baking dish and fish should then be placed on the bottom shelf of the refrigerator, which is its coolest area. Replenish the ice one or two times per day.
The length of time that tuna can stay fresh stored this way depends upon how fresh it is, i.e. when it was caught. But in general, about two days is the longest time period that we recommend refrigerating fresh fish on ice. After two days, we recommend freezing the fish if you will not be cooking it. To freeze, wrap it well in plastic and place it in the coldest part of the freezer where it will keep for up to two or three weeks.
All of these selection and storage steps for tuna are especially important due to special risk of histamine formation in tuna. Adverse reactions to histamine in tuna are often referred to as "scombrotoxic poisoning" since tuna belong to Scombridae family of fish. Failure to keep fresh tuna well chilled at refrigerator temperatures prior to cooking can result in increased histamine content and greater risk of adverse reaction. So can improper handling of canned tuna, in which a can is opened and allowed to sit at room temperature after being opened yet not consumed for several hours. The possibility of unwanted histamine formation in tuna makes it especially important for you to use care in the selection and storage of this food.
For some of our favorite recipes, click Recipes.
In 2014, the U.S. Food and Drug Administration (FDA) and U.S. Environmental Protection Agency (EPA) drafted new joint provisional guidelines for tuna consumption by pregnant women, nursing mothers, and young children. These provisional guidelines recommended 2-3 weekly servings of fish by young children on an age-appropriate and calorie-appropriate basis. Similarly, 8-12 ounces of fish representing 2-3 servings per week were recommended for pregnant women and nursing mothers. Simultaneous with this recommendation for regular intake of fish, however, was a recommendation for selection of fish lower in mercury and avoidance of higher mercury fish. With respect to tuna, these provisional guidelines, recommended a limit of 6 ounces of albacore tuna per week for pregnant women and nursing mothers, and preferential selection of light canned tuna when including tuna in weekly fish consumption.
We do not disagree with the logic of the FDA recommendations. Yet, we would also point out that "canned light tuna" may include skipjack, tongol, and yellowfin species and that some yellowfin tuna can be quite high in mercury accumulation. So as a general rule, "canned light tuna" that specify skipjack or tongol may provide you with lower mercury exposure. We would also point out that canned tuna is not the only form of tuna available in the marketplace, and that fresh tuna (including species like skipjack) is available as fresh fish option.
Based on all of the research that we have reviewed, we think it makes sense not only for pregnant women, women of childbearing age who might become pregnant, nursing mothers, and young children to limit their consumption of higher mercury fish, but for everyone who wants to include fish within their meal plan. Accordingly, we do not think it makes sense for you to rely on tuna as a primary seafood source for key nutrients, including omega-3 fats, since all tuna species show some level of mercury contamination in research studies. However, we do think it makes sense for you to treat tuna as a fish that can be enjoyed multiple times per month, especially if you select tuna types with lower mercury risk. As a general rule, we would include both skipjack and tongol tuna in this lower mercury risk category.
In some cases, we would also consider yellowfin to be in the lower mercury risk category, although this species can have widely ranging mercury level due to its widely ranging size and lifestyle. For many people who want to err on the conservative side, it might make sense to avoid yellowfin tuna altogether if you are unable to determine its status as higher or lower in mercury. Because mercury levels in oceans are continuously changing, and because they can vary so greatly from ocean to ocean and even at different water depths within an individual ocean, levels in fish—including tuna—can sometimes be difficult to predict or even determine. One resource you can to follow-up on these levels is mercury and fish information provided by the U.S. Food and Drug Administration (FDA) at this website.
If you are making a decision about tuna consumption and have actual mercury data available like the FDA data above, you can generally regard tuna with mercury levels of 100 ppb or less as being "lower" in mercury, and tuna with mercury levels of 500 ppb or more as being "higher" in mercury.
Contamination of ocean waters, overfishing of fish and shellfish species, quality of fish farming practices, potential detrimental effects of certain fishing methods on wildlife, and risk of exposure to fish contaminants (especially mercury) have become individual concerns for many consumers. (These concerns are not limited to tuna, but extend to all seafood.) Luckily, two organizations in the U.S. have worked to evaluate all the issues listed above, and offer practical recommendations for making fish choices in light of these concerns. We encourage you to make use of the resources provided by both of these organizations.
The first organization is the Monterey Bay Seafood Watch (www.seafoodwatch.org).
You can find practical recommendation for 65 different types of fish on their website, as well as Best Choices, Good Alternatives, and Choices to Avoid. You can also download seafood guides specific to your region of the United States and a mobile app providing you with this information. The Monterey Bay Seafood Watch program is associated with the Monterey Bay Aquarium in Monterey Bay, California and run by the not-for-profit Monterey Bay Aquarium Foundation.
The second organization is The National Ocean and Atmospheric Administration Fish Watch (http://www.fishwatch.gov/).
The National Ocean and Atmospheric Administration (NOAA) is a federal agency in Washington, D.C. that has used its FishWatch website to create educational, user-friendly profiles of over 100 fish and shellfish, with up-to-date information about fishing rate, habitat impacts, population, bycatch, species science, nutrient content, and marketplace availability. In comparison with the Monterey Bay Seafood Watch, the FishWatch site is more educational in nature, and is focuses on the providing of information that can be used to make informed seafood choices.
Fish, such as tuna, are among the eight food types considered to be major food allergens in the U.S., requiring identification on food labels. For helpful information about this topic, please see our article, An Overview of Adverse Food Reactions.
Tuna, yellowfin fillet, baked
GI: very low
|vitamin B3||25.03 mg||156||19.1||excellent|
|vitamin B12||2.66 mcg||111||13.5||excellent|
|vitamin B6||1.18 mg||69||8.5||excellent|
|phosphorus||377.62 mg||54||6.6||very good|
|vitamin D||92.99 IU||23||2.8||good|
|vitamin B1||0.15 mg||13||1.5||good|
|vitamin B2||0.16 mg||12||1.5||good|
Density>=7.6 AND DRI/DV>=10%
Density>=3.4 AND DRI/DV>=5%
Density>=1.5 AND DRI/DV>=2.5%