Sushi and tuna: mostly rice, and a question of mercury

Freezing fish kills the parasites that raw fish can carry, and many Japanese diners avoid it because they believe freezing ruins sushi. In a randomized double-blind taste test in Japan, diners were no more likely to pick never-frozen mackerel sushi as tastier (odds ratio 0.86, 95% CI 0.59 to 1.26). Tuna was not in that trial. A piece of tuna nigiri is mostly rice: the UK composition table gives it 170 calories, 30.3 g carbohydrate and 8.4 g protein per 3.5 oz (100 g), and one piece is coded at 35 g in US surveys. Raw tuna on its own is lean, with 25.2 g protein, 0.7 g fat, 93 micrograms selenium and 3.2 micrograms vitamin D per 3.5 oz (100 g), and only 0.09 g omega-3 fat. We found no trial or cohort on health outcomes from eating sushi or tuna as a food. The evidence we have is about safety.

How much is actually in it

• Six USDA samples of wild yellowfin tuna averaged 76.52 micrograms of selenium per 3.5 oz (100 g), while sodium swung from 26.5 to 243 mg per 3.5 oz (100 g). — USDA Foundation Foods, Tuna, ahi or yellowfin, frozen, wild caught, 6 samples Evidence E source
  Selenium 76.52 ug/100 g (range 68.7-85.0); sodium 94.37 mg/100 g (range 26.5-243.0, median 50.95); protein 24.7 g
• Tuna nigiri in the UK composition table carries 170 calories, 30.3 g carbohydrate and 8.4 g protein per 3.5 oz (100 g), mostly from the rice. — CoFID 2021 record 16-362, Sushi, tuna nigiri Evidence E source
  Per 100 g: energy 170 calories, carbohydrate 30.3 g (starch 25.5 g, sugars 4.7 g), protein 8.4 g, fat 2.5 g, n-3 PUFA 0.31 g
• Raw tuna flesh in the UK composition table carries 25.2 g protein, 93 micrograms selenium and 3.2 micrograms vitamin D per 3.5 oz (100 g), with only 0.7 g fat. — CoFID 2021 record 16-399, Tuna, flesh only, raw Evidence E source
  Per 100 g: energy 107 calories, protein 25.2 g, fat 0.7 g, n-3 PUFA 0.09 g, selenium 93 ug, vitamin D 3.2 ug, sodium 66 mg
• NIH names tuna among fatty fish whose flesh is among the best natural food sources of vitamin D. — US diet Evidence E source
  Qualitative

What a real portion looks like

• In US dietary recall coding one piece of tuna-topped sushi weighs 1.2 oz (35 g), and an unspecified portion is coded as 210 g. — FNDDS food code 58151440, Sushi, topped with tuna (fdc_id 2708971) Evidence E source
  1 piece 35 g; 1 cup 140 g; quantity not specified 210 g

What your body absorbs

• In a randomized dinner study in 9 euthyroid adults, a sushi meal with fresh seaweed salad raised urinary iodine by 385% and TSH by 150% for a day or two. — Nine euthyroid participants (n = 9) Evidence B source
  Urinary iodine +385%, +59% and +43% by group; TSH +150% on day 2, back by day 3; fT4 unchanged
• In a randomized metabolic study in 14 women aged 51-70, 7 weeks on a high-meat diet including tuna increased zinc absorption compared with a low-meat diet. — 14 women aged 51-70 y, each diet for 7 wk (n = 14) Evidence B source
  Zinc absorption and retention higher on high-meat diet; iron status lower (higher iron-binding capacity, lower ferritin)
• In a randomized trial in 60 toddlers over one month, tuna oil given as a microencapsulated powder in formula raised blood DHA more than plain tuna oil. — Sixty toddlers (n = 60) Evidence B source
  Significantly greater blood DHA with microencapsulated powders; size not in abstract

What cooking and storage change

• By the USDA table for lean finfish baked without drippings, cooking keeps 90% of vitamin B12, B6 and thiamin and all of the minerals. — USDA retention factors for Finfish and Shellfish Products, FINFISH <5% FAT, BAKED, WO/DRIPPINGS (Retn_Code 2301) Evidence E source
  Vitamin B12 90%, vitamin B6 90%, thiamin 90%, niacin 95%, riboflavin 95%; calcium, iron, zinc, potassium, sodium 100%
• In a randomized double-blind taste trial with 240 pieces of mackerel sushi, diners were no more likely to prefer never-frozen fish, with an odds ratio of 0.86. — Japanese individuals; 120 rounds of discrimination testing (n = 40) Evidence B source
  OR 0.86 (95% CI 0.59-1.26) for choosing unfrozen mackerel as tastier; squid OR 1.38 (0.93-2.05)

Safety, limits and interactions

• A meta-analysis of 103 histamine poisoning incidents found a mean of 1107 mg histamine per kg in implicated food, mostly tuna or marlin. — 55 reports, 103 incidents Evidence C source
  Mean histamine 1107.21 mg/kg (CI 422.62-2900.78); I2 100%
• Across 693 Iranian canned tuna samples, histamine averaged 77.86 mg per kg, below the FDA limit of 200 mg per kg. — 11 articles and a total of 693 samples (n = 693) Evidence C source
  Mean 77.86 mg/kg (95% CI 47.51-108.21); prevalence 9.19%
• Pooled data on 1295 Iranian canned tuna samples put mercury at 0.11 micrograms per gram, with arsenic the only metal carrying a modeled cancer risk. — 23 articles and 1295 samples (n = 1295) Evidence C source
  Hg 0.11 ug/g wet weight; As 0.38 ug/g; ILCR of As 3.21E-5 adults, 4.18E-5 children
• Of 2009 Kudoa food poisoning cases reported in Japan in 2013-2023, 99% were traced to flounder, particularly as sashimi and sushi. — Reported cases totaled 2009 (n = 2009) Evidence C source
  99% of cases implicated flounder sashimi and sushi
• A systematic review of 149 articles on warfarin lists sushi among foods that warrant awareness of increased bleeding risk. — 149 articles describing 78 herbs, food or dietary supplements Evidence C source
  Listed; size not quantified

What people believe that the data does not support

• Nationally representative US surveys found awareness of mercury in fish rose from 69% in 2001 to 80% in 2006, and women of childbearing age were less aware than other women. — Food Safety Surveys with sample sizes of 4482 in 2001 and 2275 in 2006 (n = 6757) Evidence C source
  Awareness 69% to 80% (p<.001)

Who this works differently for

• FDA and EPA list canned light tuna (including skipjack) as a Best Choice, albacore and yellowfin tuna as Good Choices, and bigeye tuna as a Choice to Avoid with the highest mercury levels. Children get 2 Best Choices servings a week, 1 to 4 ounces by age. — people who are pregnant or breastfeeding and children ages 1 to 11 years Evidence E source
  2 servings a week from Best Choices, serving about 1 ounce at age 1 to 3, 2 ounces at 4 to 7, 3 ounces at 8 to 10, 4 ounces at 11
• FDA lists raw or smoked fish among foods that can carry Listeria and advises pregnant women to avoid refrigerated smoked seafood, tuna included, unless it is in a cooked dish. Listeriosis is life-threatening especially for unborn and newborn children, adults over 65 and people with weakened immune systems. — Pregnant women, unborn and newborn children, adults over 65, people with weakened immune systems (n = -) Evidence E source
  Raw or smoked fish listed as Listeria sources, avoid refrigerated smoked seafood such as tuna unless in a cooked dish
• A systematic review of canned tuna found methylmercury hazard quotients above 1 for children in 12 countries, while cadmium, lead and nickel posed no non-cancer risk. — adults and children consumers of canned tuna Evidence C source
  THQ > 1 for MeHg in children in 12 countries and adults in Tunisia; THQ < 1 for Cd, Pb, Ni
• Among 700 three-year-olds, eating non-fried fish including tuna was linked with 120% higher toenail mercury than eating no fish. — 700 three-year-old children from the New Hampshire Birth Cohort Study (n = 700) Evidence C source
  +120% toenail Hg (95% CI 82%, 164%) for other fish including tuna vs none
• Among 108 children with IgE-mediated fish allergy in Singapore, most tolerated another fish species, and 24.1% tolerated tuna. — 108 children with fish allergy (n = 108) Evidence C source
  75.9% tolerate another fish; tuna 24.1%; anaphylaxis 6.5%
• FDA and EPA advise people who are pregnant or breastfeeding to eat 8 to 12 ounces of lower-mercury seafood per week. — people who are pregnant or breastfeeding Evidence E source
  8-12 oz per week of lower-mercury seafood
• The FDA and EPA fish chart lists bigeye tuna among the choices to avoid because of the highest mercury levels. — people who are or might become pregnant, breastfeeding, and children Evidence E source
  Bigeye tuna: choice to avoid, highest mercury levels

What is still unknown

• The USDA systematic review of seafood in pregnancy found that most studies did not separate seafood types, so tuna cannot be judged apart from other fish. — cohort studies of maternal seafood intake and child language development Evidence C source
  Evidence gap

The bottom line

The FDA and EPA advise people who are pregnant or breastfeeding to eat 8 to 12 ounces a week of seafood lower in mercury, and their chart lists bigeye tuna among the choices to avoid for its high mercury. That advice is about how much and which fish, and the 8 to 12 ounces is a weekly total for lower-mercury seafood, not an amount of tuna. On this page only bigeye tuna is placed on the chart, and we have no card on the limits for other tuna species, on eating raw fish such as sushi while pregnant, or on fish portions for children. If you are pregnant or feeding a child, take the species and the amount to your midwife or doctor before counting tuna sushi toward that figure. For children, modeled exposure from canned tuna put methylmercury hazard quotients above 1 in 12 countries, a risk estimate rather than measured harm. Among 700 three-year-olds in New Hampshire, eating non-fried fish including tuna was linked with 120 percent higher toenail mercury (95% CI 82 to 164 percent) than eating no fish, a biomarker with no health outcome attached. The USDA review of seafood in pregnancy could not judge tuna on its own, because most studies did not separate seafood types. Tuna and marlin dominate histamine poisoning. Across 103 incidents, the implicated fish held a mean of 1107 mg histamine per kg (CI 422.62 to 2900.78), and the outbreak reports disagreed hugely with each other. Canned tuna tested in Iran averaged 77.86 mg per kg, below the FDA limit of 200, in one country's product. Pooled Iranian data put mercury in canned tuna at 0.11 micrograms per gram and found arsenic the only metal carrying a modeled cancer risk. Of 2009 Kudoa food poisoning cases in Japan from 2013 to 2023, 99 percent came from flounder, especially as sashimi and sushi, so this risk belongs to flounder. A review of warfarin interactions lists sushi among foods that warrant awareness of bleeding risk, without a size or a reason. If you take warfarin, mention sushi to the person who manages your dose. In nine adults with normal thyroid function, a sushi dinner with fresh seaweed salad raised urinary iodine by up to 385 percent and TSH by 150 percent, and TSH was back to baseline by day three. Among 108 children with fish allergy at one Singapore center, most tolerated another species, and 24.1 percent tolerated tuna. Sodium in six USDA samples of frozen yellowfin ranged from 26.5 to 243 mg per 3.5 oz (100 g), which the dataset notes likely reflects brine used in processing. By the USDA table for lean baked fish, cooking keeps 90 percent of vitamin B12 and all of the minerals, a group factor not measured on tuna. In 14 women aged 51 to 70, seven weeks on a high-meat diet with tuna as one of four protein foods raised zinc absorption compared with a low-meat diet. In US surveys, awareness of mercury in fish rose from 69 percent in 2001 to 80 percent in 2006.

Sources

1. sstu-daily-r6-01 · USDA Foundation Foods dataset
   Tuna, ahi or yellowfin, frozen, wild caught: Selenium, Se 76.52 UG, range 68.7-85.0 (median 76.3), 6 samples; Sodium, Na 94.37 MG, range 26.5-243.0 (median 50.95), 6 samples; Protein 24.7 G
   USDA FoodData Central, Foundation Foods, release 2026-04-30, Tuna, ahi or yellowfin, frozen, wild caught · checked 2026-09-29
2. sstu-daily-r6-02 · CoFID dataset
   CoFID 16-362 Sushi, tuna nigiri: Energy (kcal) 170; Carbohydrate (g) 30.3; Starch (g) 25.5; Total sugars (g) 4.7; Protein (g) 8.4; Fat (g) 2.5; n-3 poly /100g food (g) 0.31
   CoFID 2021 (Public Health England), code 16-362 · checked 2026-09-29
3. sstu-daily-r6-03 · CoFID dataset
   CoFID 16-399 Tuna, flesh only, raw: Energy (kcal) 107; Protein (g) 25.2; Fat (g) 0.7; n-3 poly /100g food (g) 0.09; Selenium (µg) 93; Vitamin D (µg) 3.2; Sodium (mg) 66
   CoFID 2021 (Public Health England), code 16-399 · checked 2026-09-29
4. sstu-daily-r6-19 · NIH ODS fact sheet
   The flesh of fatty fish (such as trout, salmon, tuna, and mackerel) and fish liver oils are among the best sources [17,1].
   NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals · checked 2026-09-29
5. sstu-daily-r6-04 · FNDDS dataset
   FNDDS 58151440 Sushi, topped with tuna: 1 piece 35 g; 1 cup 140 g; Quantity not specified 210 g
   USDA FNDDS 2021-2023, food code 58151440 · checked 2026-09-29
6. sstu-daily-r6-07 · RCT
   UIE rose (p < 0.001) by 385%, 59% and 43% for groups A, B, and C, peaked in the 6-h spot urine sample at 393, 120, and 109 µg/g, and was down to pre-meal values by day 2. Serum TSH rose (p = 0.012) 150% on day 2 and was down to pre-meal values by day 3.
   J Endocrinol Invest, 2020 · checked 2026-09-29
7. sstu-daily-r6-08 · RCT
   Lean beef, chicken, ham, and tuna in the HM diet replaced foods with a low mineral content in the LM diet. ... Compared with the other diets, the HM diet increased zinc absorption and retention, and slightly increased urinary zinc.
   Am J Clin Nutr, 1995 · checked 2026-09-29
8. sstu-daily-r6-09 · RCT
   The results showed an enhanced bioavailability with significantly greater concentrations of blood DHA levels in formulas with microencapsulated powders.
   Nutrients, 2020 · checked 2026-09-29
9. sstu-daily-r6-05 · USDA Table of Nutrient Retention Factors, dataset
   USDA-RETN-R6:2301 FINFISH,<5%FAT,BAKED,WO/DRIPPINGS: vitamin_b12_ug 90%; vitamin_b6_mg 90%; thiamin_mg 90%; niacin_mg 95%; riboflavin_mg 95%; zinc_mg 100%; iron_mg 100%
   USDA Table of Nutrient Retention Factors, Release 6, 2007, Retn_Code 2301 · checked 2026-09-29
10. sstu-daily-r6-06 · RCT
    This risk of infection can be eliminated by freezing fish; however, Japanese people are hesitant to freeze fish because it is believed that freezing ruins sushi's taste. ... The odds ratio for selecting unfrozen sushi as "tastes better" over frozen sushi was 0.86 (95% confidence interval [CI], .59-1.26; P = .45).
    Clin Infect Dis, 2015 · checked 2026-09-29
11. sstu-daily-r6-10 · systematic review and meta-analysis
    histamine mean concentration in poisoning samples was 1107.21 mg/kg with confidence interval for the meta-mean of 422.62-2900.78 mg/kg; heterogeneity index (I2) was 100% (P < 0.0001); prediction interval was 24.12-50822.78 mg/kg. Fish involved in histamine poisoning was mainly tuna or Istiophoridae species.
    Crit Rev Food Sci Nutr, 2018 · checked 2026-09-29
12. sstu-daily-r6-11 · systematic review and meta-analysis
    The mean concentration was calculated as 77.86 mg kg−1 (95% confidence interval [CI], 47.51 to 108.21 mg kg−1), which was lower than the 200 mg kg−1 recommended limit by the U.S. Food and Drug Administration (FDA).
    J Food Prot, 2018 · checked 2026-09-29
13. sstu-daily-r6-13 · systematic review and meta-analysis
    Adults and children that consume canned tuna fish in Iran are not at non-carcinogenic risk but have a carcinogenic risk due to As.
    Food Chem Toxicol, 2018 · checked 2026-09-29
14. sstu-daily-r6-16 · cohort
    Flounder, particularly sashimi and sushi, were implicated in 99% of cases.
    Sci Rep, 2026 · checked 2026-09-29
15. sstu-daily-r6-17 · systematic review
    These include Chinese wolfberry, chamomile tea, cannabis, cranberry, chitosan, green tea, Ginkgo biloba, ginger, spinach, St. John's Wort, sushi and smoking tobacco.
    Br J Clin Pharmacol, 2021 · checked 2026-09-29
16. sstu-daily-r6-18 · cross-sectional
    Our results indicated an increase in consumers' awareness of mercury as a problem in fish (69% in 2001 to 80% in 2006, p<.001).
    Environ Res, 2011 · checked 2026-09-29
17. sf-fish-r2-4 · agency advice
    1 ounce at age 1 to 3 2 ounces at age 4 to 7 3 ounces at age 8 to 10 4 ounces at age 11 Eat 2 servings a week from the “Best Choices” list. ... Tuna, canned light (includes skipjack) Best Choice ... Tuna, albacore/white tuna, canned and fresh/frozen Good Choice ... Tuna, yellowfin Good Choice ... Tuna, bigeye Choice to Avoid: HIGHEST MERCURY LEVELS
    FDA and EPA, Advice about Eating Fish · checked 2026-10-08
18. sf-lrs-r3-6 · agency advice
    You can get listeriosis by eating raw, unpasteurized milk ... raw or smoked fish and other seafood. ... Refrigerated smoked seafood - unless it's in a cooked dish, such as a casserole. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna, or mackerel, is most often labeled as "nova-style," "lox," "kippered," "smoked," or "jerky." ... Listeriosis is a life-threatening disease, especially for unborn or newborn children, adults over the age of 65, and those with weakened immune systems.
    US FDA, Listeria (Food Safety for Moms-to-Be) · checked 2026-10-08
19. sstu-daily-r6-12 · systematic review
    Moreover, the THQ value due to Me Hg for adult in Tunisia and for children in Tunisia, Malta, Portugal, Latvia, Cambogia, Peru, South Korea, Romania, Hong Kong, United Arab Emirates, Morocco, and Egypt was higher than 1 value.
    Int J Environ Health Res, 2024 · checked 2026-09-29
20. sstu-daily-r6-14 · cohort
    To a lesser extent, children consuming "other fish (not fried) including tuna" and "fried fish or fish sticks" had 120% (95% CI: 82%, 164%), and 23% (95% CI: 2%, 51%) higher toenail concentrations, respectively, than those consuming no fish.
    Environ Res, 2024 · checked 2026-09-29
21. sstu-daily-r6-15 · cohort
    Anaphylaxis occurred in 6.5%. ... Most can tolerate another species of fish (75.9%), most commonly salmon (37.0%), tuna (24.1%) and cod (22.2%).
    Asian Pac J Allergy Immunol, 2025 · checked 2026-09-29
22. sstu-daily-r6-20 · FDA/EPA advice
    Those who are pregnant or breastfeeding consume between 8 and 12 ounces per week of a variety of seafood from choices that are lower in mercury.
    FDA/EPA, Advice about Eating Fish, 2024 · checked 2026-09-29
23. sstu-daily-r6-21 · FDA/EPA advice
    Tuna, bigeye
    FDA/EPA, Advice about Eating Fish, 2024 · checked 2026-09-29
24. sstu-daily-r6-22 · USDA NESR systematic review
    The type of seafood consumed, which may be an important variable, was not considered in most studies; the one study that considered shellfish and squid separately from fish found divergent results by type.
    USDA NESR, Seafood Consumption during Pregnancy and Lactation and Neurocognitive Development in the Child, 2020 · checked 2026-09-29