Tuna is not one fish. The tribe Thunnini holds 15 species in five genera, and the tuna in most light cans is skipjack. Under US rules only albacore, Thunnus alalunga, may be labeled white tuna, while “light” is defined by meat color rather than by species.
Tuna are also unusual among fish because they keep their bodies warmer than the water. A network of blood vessels called the rete mirabile recaptures muscle heat, and a bluefin can hold a core temperature of 25 to 33 °C in water as cold as 6 °C. The meat itself is a mix of light and dark muscle in roughly equal parts.
Skipjack is a lean fish. Raw, it has 22 g of protein and 1 g of fat per 100 g, ranks 6th of 132 foods on this site for protein, and has more niacin per 100 g than any other food compared here. It has little of the omega-3 oil fish are known for, only 0.26 g of EPA plus DHA per 100 g. Mercury is the main thing to watch, and it depends heavily on which tuna is in the can.
Health benefits of tuna
No study of tuna as a food reaches strong evidence, and the strongest result below is about capsules: fish oil lowered triglycerides by about 15% but not deaths or heart events. Skipjack has little of that oil, with about 0.22 g of EPA and DHA in 3 oz (85 g) raw, against the 1 g a day used in the large capsule trial. For tuna itself, the best-supported finding comes from older US adults, where eating tuna or other broiled or baked fish went with lower risks of heart disease death, stroke, heart failure and atrial fibrillation, while fried fish did not. Here is what 22 studies found, strongest evidence first, from supplement trials and cohorts to mercury in pregnancy and lab work.
Omega-3 fish oil capsules cut triglycerides by about 15% but made little or no difference to deaths or heart events
Cochrane review of 86 randomized trials (162,796 people) lasting at least 12 months, mostly testing capsules rather than fish. Deaths from any cause (risk ratio 0.97) and cardiovascular events (0.96) barely changed, while coronary heart disease events fell slightly (0.91). These were supplements, not tuna, and the authors found little evidence about eating fish.
A 1 g daily marine omega-3 capsule did not lower major cardiovascular events or cancer in 25,871 older adults
Placebo-controlled randomized trial in the US (men 50 and older, women 55 and older), followed for a median of 5.3 years. Major cardiovascular events had a hazard ratio of 0.92, not significant, while total heart attacks had 0.72 (95% CI 0.59 to 0.90). A supplement, not fish. Funded by the National Institutes of Health and others.
Selenium-enriched skipjack tuna nuggets eaten for 12 weeks lowered LDL cholesterol by 12.9 mg/dL in people with ischemic cardiomyopathy
Randomized trial of 120 patients in Lahore, Pakistan: 60 ate the nuggets and 60 had standard dietary care. The tuna group also lost 1.8 kg more, and had lower triglycerides (14.1 mg/dL), higher HDL (4.6 mg/dL) and lower hs-CRP (0.9 mg/L). These were fortified nuggets, not plain tuna, with no placebo food, one hospital and a short follow-up.
A high dose of tuna extract lowered uric acid by 0.41 mg/dl four weeks after a 4-week course, against a rise of 0.11 with placebo
Randomized, double-blind trial of 48 men without gout who had slightly high uric acid, split into low-dose, high-dose and placebo groups. During the course uric acid fell 0.23 and 0.34 mg/dl in the extract groups against 0.07 on placebo; only the high-dose result after the course is reported as significant. It tested an extract of imidazole compounds, not tuna meat, and the authors work for Yaizu Suisankagaku Industry.
Show 18 more studies
Adults 65 and older who ate tuna or other broiled or baked fish 3 or more times a week had a 49% lower risk of dying from ischemic heart disease than those eating it less than once a month
Cohort of 3,910 US adults followed for 9.3 years on average (Cardiovascular Health Study). The drop was 58% for arrhythmic heart deaths, and nonfatal heart attacks were not linked to intake. Fried fish and fish sandwiches showed no benefit, only trends toward higher risk. The group mixes tuna with other broiled or baked fish.
Older adults who ate tuna or other broiled or baked fish 1 to 4 times a week had a 27% lower risk of ischemic stroke, while fried fish went with a 44% higher risk
Cohort of 4,775 adults aged 65 and older followed for 12 years, with 626 strokes. Eating it 5 or more times a week went with 30% lower risk (hazard ratio 0.70). Fish was not linked to hemorrhagic stroke. This is a link, not proof, and the group mixes tuna with other broiled or baked fish.
Older adults who ate tuna or other broiled or baked fish 3 to 4 times a week had a 31% lower risk of heart failure than those eating it less than once a month
Cohort of 4,738 adults aged 65 and older followed for 12 years, with 955 new cases of heart failure. Eating it 1 to 2 times a week went with 20% lower risk, and 5 or more times a week with 32% lower risk, a result that narrowly missed significance (95% CI 0.45 to 1.03). Fried fish went with higher risk.
Older adults who ate tuna or other broiled or baked fish 1 to 4 times a week had a 28% lower risk of atrial fibrillation than those eating it less than once a month
Cohort of 4,815 adults aged 65 and older, with 980 cases of atrial fibrillation over 12 years. Eating it 5 or more times a week went with 31% lower risk (hazard ratio 0.69). Fried fish and fish sandwiches were not linked to lower risk. The group mixes tuna with other broiled or baked fish.
Each extra 20 g of fish a day went with a 4% lower risk of dying from cardiovascular disease and only a marginal drop in deaths from any cause
Meta-analysis of 14 cohort studies with 911,348 participants and 75,451 deaths: relative risk 0.96 for cardiovascular death and 0.98 for death from any cause. The link was significant only in Asian studies, while Western studies suggested a U shape with the lowest risk near 20 g a day. It covers all fish, not tuna alone.
People with higher mercury in their toenails did not have a higher risk of cardiovascular disease in two large US cohorts
Study of 3,427 people who developed cardiovascular disease, matched to controls, drawn from cohorts of 51,529 men and 121,700 women. Comparing the top and bottom fifths of toenail mercury, the relative risk for total cardiovascular disease was 0.85 (95% CI 0.72 to 1.01), at the exposure levels seen in US adults. Funded by the National Institutes of Health.
Children of women who ate no seafood in pregnancy had 48% higher odds of a low verbal IQ than children of women who ate more than 340 g a week
Cohort of 11,875 pregnant women in the Avon Longitudinal Study (ALSPAC), with children followed from 6 months to 8 years. Women who ate some seafood (1 to 340 g a week) had an odds ratio of 1.09, not significant. The authors concluded that advice to limit seafood could be harmful. It covers all seafood and is observational.
Children whose mothers had mercury in the top 10% scored 4.5 points lower on a vocabulary test at age 3, even though more fish went with better scores
Cohort of 341 mother-child pairs in Massachusetts. Mean fish intake was 1.5 servings a week, and eating more than 2 servings a week went with a 6.4-point higher visual-motor score. Eating 2 servings a week or less showed no benefit. The authors say advice for pregnant women should weigh both the benefits and the risks.
In the Seychelles, where mothers ate fish about 12 times a week, prenatal mercury was linked to only two of many test results in children at age 9
Cohort of 779 mother-infant pairs, with a mean prenatal mercury level of 6.9 ppm in maternal hair. Higher exposure went with a weaker grooved pegboard score in boys using the non-dominant hand, and with a better teacher-rated hyperactivity score. The authors say the data do not support a risk from ocean fish alone. Seychelles fish carry about the same mercury as commercial ocean fish elsewhere.
Prenatal mercury from fish had no overall adverse link to child development at 20 months among 1,265 Seychelles mother-child pairs
Observational cohort in a high-fish-eating population. Higher mercury went with lower psychomotor scores only in children of mothers with a higher n-6 to n-3 fatty acid ratio, and with better scores among mothers with higher n-3 fats. The authors suggest that fatty acid balance may change how mercury acts.
In 286 autopsied brains of older adults, seafood eaters had more mercury, but higher brain mercury was not linked to more brain damage
Cross-sectional study of deceased Chicago participants (average age 89.9) in the Memory and Aging Project. Brain mercury rose with seafood meals per week (correlation 0.16). Eating seafood at least once a week went with less Alzheimer disease pathology, but only in carriers of the APOE e4 gene.
Three-year-olds who ate “other fish including tuna” had 120% higher toenail mercury than children who ate no fish
Cohort of 700 children in the New Hampshire Birth Cohort Study. Any fish went with 108% higher toenail mercury, and fried fish or fish sticks with 23% higher, and 23% of children ate at least one fish meal a week. The tuna group is mixed with other non-fried fish, and the authors say the health effects of this exposure remain to be determined.
University students who ate tuna in campus dining halls had hair mercury of 0.466 µg/g, against 0.110 µg/g in students who did not
Study of 20 tuna eaters and 33 non-eaters. More than half of the tuna eaters (54%) reported 3 or more tuna meals a week, which could exceed the EPA reference dose for methylmercury, and 7% of participants reported more than 20 tuna meals a week, linked to hair mercury above 1 µg/g. Small and based on self-reported intake.
A fisherman who ate tuna at two or more meals a day for 2 years developed mercury poisoning with leg pain and tingling
Case report of one 48-year-old man. Two months after he stopped eating tuna his blood mercury was 21.79 µg/l, estimated at 38.70 to 53.20 µg/l while at sea, and it fell to 14.18 µg/l after four months as his symptoms nearly cleared. One case shows what extreme intake can do, not what ordinary servings do.
In a lab digestion model, less than 20% of the mercury in canned tuna was bioaccessible, against 39 to 48% in cooked tuna
Raw, boiled, grilled and canned tuna of the genus Thunnus was digested in a test tube to see how much selenium and methylmercury could be absorbed. In the bioaccessible fraction selenium outnumbered mercury 10 to 74 times, by molar ratio. This was not a study in people, and the authors judged raw, boiled and grilled tuna riskier than canned for pregnant and nursing women.
Tuna protein hydrolysate lowered blood pressure, blood sugar and cholesterol in rats fed a high-fat diet
Rats ate a high-fat diet for 16 weeks and got the hydrolysate (100, 300 or 500 mg/kg) or metformin for the last four weeks, with 8 rats per group. The hydrolysate and metformin had comparable effects. A hydrolysate is tuna protein broken into small pieces, not tuna meat, and rat results often do not carry over to people.
In obese diabetic mice, replacing half the protein with tuna dark muscle protein raised HDL cholesterol and lowered liver fat
Four-week-old male KK-Ay mice ate a casein diet or one in which 50% of the protein came from tuna dark muscle for 4 weeks. The authors tie the changes to gene activity in fat tissue and liver. A short mouse study in a strain bred to be obese and diabetic.
Rats fed tuna protein plus cholesterol had higher blood and liver cholesterol than rats fed cod protein
Male Wistar rats ate 23% protein from casein, cod or tuna, with or without 0.5% cholesterol and 0.1% sodium cholate. On the cholesterol diet the tuna group had more serum and liver cholesterol than the cod group, though it excreted more fecal sterols. A mixed rat result, not a test in people.
Who should be careful with tuna
Most people can eat tuna freely. Take a little care if one of these applies:
- Pregnancy, breastfeeding and young children. The FDA and EPA chart ranks canned light tuna (which includes skipjack) a Best Choice, albacore and yellowfin Good Choices, and bigeye a Choice to Avoid. For people who are pregnant or breastfeeding that means 2 to 3 servings a week of Best Choices or 1 serving of a Good Choice, and for children 2 servings a week of Best Choices. A serving is 4 oz for adults, about the size of your palm, and about 1 oz at ages 1 to 3, 2 oz at 4 to 7, 3 oz at 8 to 10 and 4 oz at 11.
- Badly stored tuna (histamine poisoning). Tuna that was not kept cold can build up histamine, which freezing, cooking and canning do not remove, and smell and taste cannot reliably detect it. Flushing, a peppery burning in the mouth, headache or rash starts within minutes to 2 hours and usually passes in 4 to 6 hours; see a doctor and say what you ate.
- Fish allergy. Fish is one of the nine major US food allergens, and labels must name the species. A review notes that canning may make tuna less allergenic, but only an allergist should test that.
How to choose, store and eat tuna
- Canned light (skipjack): the lowest-mercury canned type, a mean of 0.126 ppm in FDA tests against 0.350 ppm for canned albacore. In 168 cans, light averaged 0.118 ppm and white 0.407 ppm, and packing in oil or water or draining the can made no difference.
- Fresh or frozen steaks: yellowfin averaged 0.354 ppm, albacore 0.358 ppm and bigeye 0.689 ppm in FDA data. Cook steaks to 145 °F, and buy them only from a cold counter.
- Broiled or baked, not fried: in older US adults, tuna or other broiled or baked fish 1 to 4 times a week went with 27% lower risk of ischemic stroke, while fried fish went with a 44% higher risk.
On labels, only albacore may be called white tuna, and light tuna had under a third of its mercury in the 168-can study. Fresh tuna should smell mild and have firm flesh that springs back when pressed. Keep it at 40 °F or below and use it within 2 days, or freeze it. Because mercury is in the flesh, the way to cut it is to choose the type, not to drain or rinse the can.
Sources
- Advice about eating fish. FDA and EPA.
- Mercury levels in commercial fish and shellfish (1990-2012). FDA.
- Burger J, Gochfeld M. Mercury in canned tuna: white versus light and temporal variation. Environ Res. 2004.
- Scombrotoxin poisoning and decomposition. FDA.
- Scombroid fish poisoning associated with tuna steaks, Louisiana and Tennessee, 2006. CDC, MMWR. 2007.
- Selecting and serving fresh and frozen seafood safely. FDA.
- Food allergies. FDA.
- 21 CFR 161.190: Canned tuna. US Code of Federal Regulations.
- Pecoraro L, Tenero L, Pietrobelli A, et al. Canned tuna tolerance in children with IgE-mediated fish allergy: an allergological and nutritional view. Minerva Pediatr. 2020.
History of tuna
The word tuna comes from Spanish atún, which came from Andalusian Arabic. The genus name Thunnus comes from the Ancient Greek thýnnos, the word for Atlantic bluefin, and the tuna tribe was named by Edwin Chapin Starks in 1910.
People have fished bluefin around the Mediterranean for a very long time. The Phoenician method called almadraba, a maze of nets that traps the fish, is still used in Portugal, Spain, Morocco and Italy. Ancient DNA work used bluefin specimens from archaeological sites dating from the 2nd century BCE to the 15th century CE, and catch records show the Mediterranean population rising and falling since at least the 16th century.
Canned tuna as Americans know it began in California. According to NOAA Fisheries, a cannery in San Pedro was packing mackerel and sardines in the late 1800s, and in 1903 one of its workers perfected canning albacore with steam. In 1914 the Van Camp brothers bought the California Tuna Company he later founded, and in 1930 Van Camp began selling tuna as Chicken of the Sea.
Light tuna came later and from a different fish. Japanese fishermen used bamboo poles and lines to catch skipjack off Japan and introduced the method to US fishermen, which changed fishing out of San Pedro. A cannery founded in 1917 as the French Sardine Company of California later became StarKist.
Bluefin went the other way. Overfishing depleted Atlantic bluefin in the late 20th and early 21st century, while Japan first raised farm-hatched bluefin in 1979 and closed the breeding cycle in 2002. In 2019 a 278 kg bluefin sold in Tokyo for 333.6 million yen, about US$3.1 million, the highest price paid for a single fish.
Sources
- Tuna. Wikipedia.
- Andrews AJ, Puncher GN, Bernal-Casasola D, et al. Ancient DNA SNP-panel data suggests stability in bluefin tuna genetic diversity despite centuries of fluctuating catches in the eastern Atlantic and Mediterranean. Sci Rep. 2021.
- Voices from the Fisheries: pioneers of the West Coast tuna industry. NOAA Fisheries.
Frequently asked questions about tuna
Is tuna good for you?
For most people, yes, if you choose the type with care. Raw skipjack tuna has 22 g of protein and 1 g of fat per 100 g, and 3 oz (85 g) covers 82% of the daily value of niacin and 56% of selenium. In older US adults, tuna or other broiled or baked fish 1 to 4 times a week went with 27% lower risk of ischemic stroke. That is a link, not proof, and mercury depends on the type.
Can you eat tuna every day?
Daily tuna is not what the official advice describes. In a study of university students, 54% of tuna eaters reported 3 or more tuna meals a week, which could exceed the EPA reference dose for methylmercury, and a fisherman who ate tuna at two or more meals a day for 2 years developed mercury poisoning. The FDA chart for pregnancy and children sets 2 to 3 servings a week of Best Choices such as canned light tuna, or 1 serving of albacore.
Is tuna high in mercury?
It depends on the type. FDA tests found a mean of 0.126 ppm in canned light tuna, 0.350 ppm in canned albacore, 0.354 ppm in fresh or frozen yellowfin and 0.689 ppm in fresh or frozen bigeye. In 168 cans, white tuna averaged 0.407 ppm against 0.118 ppm for light, and draining did not help. Higher mercury was not tied to more cardiovascular disease in a large US toenail study, but the official advice for pregnancy and children still limits it.
Is tuna safe during pregnancy?
Yes, in the right type and amount. The FDA and EPA list canned light tuna as a Best Choice (2 to 3 servings of 4 oz a week), albacore and yellowfin as Good Choices (1 serving a week) and bigeye as a Choice to Avoid. In a Massachusetts cohort, higher maternal mercury went with lower child test scores, while in a cohort of 11,875 women, children of those who ate no seafood had 48% higher odds of a low verbal IQ. Ask your clinician about your own diet.
Is tuna high in protein?
Yes. Raw skipjack tuna has 22 g of protein per 100 g, or 18.7 g in 3 oz (85 g), which is 91% of its 88 calories. It is a complete protein with all essential amino acids, and it ranks 6th of 132 foods on this site for protein. These figures are for raw skipjack, and canned tuna differs.
Is tuna good for your heart?
Cohort studies say possibly, while trials of fish oil say little. In older adults, tuna or other broiled or baked fish 3 or more times a week went with 49% lower risk of dying from ischemic heart disease, and 1 to 4 times a week with 28% lower risk of atrial fibrillation, but fried fish did not. In a Cochrane review of 86 trials, omega-3 capsules cut triglycerides by about 15% but did little for deaths or events, and skipjack has only about 0.22 g of EPA and DHA in 3 oz.
Is tuna good for your brain?
No trial has tested tuna for brain health, and the evidence is observational. In 286 autopsied older adults, eating seafood at least once a week went with less Alzheimer disease pathology, but only in carriers of the APOE e4 gene, and higher brain mercury was not linked to more damage. In pregnancy, children of women who ate no seafood had 48% higher odds of a low verbal IQ, while in another cohort top-decile maternal mercury went with a 4.5-point lower vocabulary score.
Is tuna good for weight loss?
No study here tested weight loss with plain tuna. In a 12-week trial of 120 heart patients, those who ate selenium-enriched tuna nuggets lost 1.8 kg more than controls, but the nuggets were a fortified product. Raw skipjack has 88 calories and no carbohydrate in 3 oz, so it fills a plate cheaply, but that is a swap effect rather than a proven effect of tuna.