Scallops: a lean shellfish with almost no science of its own

Nobody has run a trial in which people ate scallops. That is the first thing to know about this page. The one randomised study with scallop in its name tested a capsule, 1 mg a day of plasmalogens extracted from scallops, in 66 Japanese adults over 40 with below-average verbal memory. After 12 weeks their memory score was 10 points higher than on placebo, with a confidence interval that starts at 0.4 and nearly touches zero. That result says nothing about eating the shellfish. As a food, scallops are lean and mostly water. Raw frozen sea scallops in the USDA samples give 13.5 g of protein and about 16 µg of selenium per 100 g. The British steamed figure is 23 g and 51 µg, partly because steaming drives water from 82 g to 73 g per 100 g and partly because the species and the sampling differ. Everything else we can say about scallops comes from studies of shellfish or fish in general: mercury, allergy, norovirus, diabetes. Where the clinical evidence is about scallops themselves, it is two single-patient case reports.

The numbers, per 100 g

How much is actually in it

• Raw frozen sea scallops carry about 16 µg of selenium and 13.5 g of protein per 100 g in USDA Foundation samples, while British steamed scallops show 51 µg and 23 g. Part of that gap is water lost in steaming, from 82 g to 73 g per 100 g, and the rest is species and sampling. — USDA Foundation Foods sea scallops (six samples) and bay scallops (six samples), frozen, wild caught; CoFID Scallops, steamed; USDA retention factors for shellfish without shell, steamed (n = USDA 6 + 6 samples; CoFID one entry; USDA-RETN-R6 code 2770) Evidence E source
  USDA sea scallops per 100 g: selenium 15.74 µg (range 9.71 to 29.6), protein 13.5 g (9.3 to 16.3), water 82.5 g; bay scallops selenium 28.4 µg (14.4 to 36.6), protein 16.4 g. CoFID 16-262 steamed per 100 g: 118 kcal, protein 23.2 g, water 73.1 g, selenium 51 µg, vitamin B12 9.0 µg, iodine 20 µg. USDA-RETN-R6:2770 SHELLFISH,WO/SHELL,STEAMED retains vitamin B12 90%, folate 75%, phosphorus 75%, potassium 90%, iron 90%

What a real portion looks like

• The FDA and EPA fish advice lists scallop among the Best Choices, the lowest-mercury group, and tells pregnant and breastfeeding women to eat 2 to 3 servings a week from that list, a serving being 4 ounces. — Pregnant and breastfeeding women and young children in the United States Evidence E source
  Scallop in Best Choices; 2 to 3 servings a week; 1 serving 4 ounces for adults, 1 to 4 ounces for children by age
• One cooked scallop weighs about 15 g and a cup about 135 g in the USDA portion table. A restaurant plate of five or six sea scallops is therefore roughly 75 to 90 g, close to the 85 g the table uses when no quantity is given. — Scallops, steamed or boiled, FNDDS, WWEIA category Shellfish (n = FNDDS 5,432 foods, 22,046 household measures) Evidence E source
  1 scallop 15 g, 1 cup 135 g, quantity not specified 85 g

What cooking and storage change

• Bivalve molluscs concentrate norovirus by filter feeding, and a review of two decades of outbreaks reports that high viral loads persist after depuration and typical food preparation steps, which is why raw or lightly cooked bivalves are a recurring outbreak vehicle. — Norovirus outbreaks linked to bivalve molluscs over 18 years, worldwide Evidence E source
  Bivalves are a common outbreak vehicle; viral loads persist after depuration and typical preparation

What it does to your health

• In 66 healthy Japanese adults over 40 with below-average verbal memory, 1 mg a day of scallop-derived plasmalogens for 12 weeks raised the standardised verbal memory score by 10 points more than placebo, with a confidence interval that nearly touches zero. — 68 randomised, 66 analysed, cognitively healthy Japanese adults aged 40 and over with below-average verbal memory (n = 66) Evidence B source
  Verbal memory estimated marginal mean difference 10.1 (95% CI 0.4 to 19.9, p = 0.042); BDNF no between-group difference; no adverse events
• A meta-analysis of individual participant data from 28 prospective cohorts with 956,122 people derived estimates for total fish, shellfish and other fish types, but reports no shellfish-specific figure. In men all associations were null, and in women the rate was 2% higher per 100 g a week of total fish. — 956,122 adults in 28 prospective cohorts from four regions, 48,084 incident cases of type 2 diabetes (n = 956,122) Evidence C source
  Women: IRR 1.02 (95% CI 1.01 to 1.03) per 100 g/week total fish, 1.04 fatty fish, 1.02 lean fish; men: all associations null

Safety, limits and interactions

• In 102 healthy adults aged 48 to 76, eating 1 kg of fish and mussels a week for 26 weeks raised whole-blood mercury by 5.1 ng/ml, arsenic by 7.1 ng/ml and lead by 2.6 ng/ml compared with controls. The authors judged the levels of no health concern except for lead. — 102 healthy non-smoking Norwegian men and women aged 48 to 76, 51 per arm (n = 102) Evidence B source
  Difference in mean change vs control: mercury 5.1 ng/ml (95% CI 4.4 to 5.8), arsenic 7.1 (5.0 to 9.2), lead 2.6 (0.0 to 5.2); cadmium mostly below detection
• In a 14-year-old girl with shrimp allergy who reacted to scallops after exercise, IgE bound the same 38 kDa band in shrimp, crab and scallop and inhibition tests showed cross-reactivity, pointing to tropomyosin as the shared allergen. — One 14-year-old girl with shrimp allergy, Japan (n = 1) Evidence D source
  Serum IgE reacting with 38 kDa bands for shrimp, crab and scallops; dot-blot inhibition showed cross-reactivity

Who this works differently for

• Across 93 European studies, self-reported lifetime shellfish allergy is 0.4% and food-challenge-verified shellfish allergy is 0.1%, the second lowest of the eight big allergens after fish. — European population studies published 2000 to 2021, all age groups (n = 93 studies) Evidence C source
  Self-reported lifetime prevalence 0.4% (95% CI 0.3 to 0.6); challenge-verified point prevalence 0.1% (0.0 to 0.2)
• A worldwide systematic review of 61 studies put shellfish allergy at 0% to 10.3% by questionnaire but only 0% to 0.9% where food challenges were used, and found it may be more common in Southeast Asia. — Population-based cross-sectional and cohort studies worldwide, 61 studies (n = 61 studies) Evidence C source
  Shellfish allergy prevalence 0 to 10.3% self-reported, 0 to 0.9% by food challenge; fish 0 to 7% and 0 to 0.3%
• Among 127,310 allergen tests in a Shanghai children's hospital from 2020 to 2024, lobster or scallop specific IgE was positive in 5.27% of children aged 0 to 3, the age at which shellfish sensitisation was highest. — Children aged 0 to 18 tested for allergen-specific IgE at Shanghai Children's Hospital, 127,310 tests (n = 127,310 tests) Evidence C source
  Lobster/scallop sIgE positive 5.27% at age 0 to 3; shrimp 8.27%, crab 8.13%, mussel 2.89% in the same age group

What is still unknown

• A scoping review of 46 studies on shellfish in pregnancy, lactation and the first two years found consumption linked to higher contaminant biomarkers, mercury above all, no association with preterm birth, mixed results for birth weight, and no data on child development. — Pregnant and lactating women and children aged 0 to 2 in 46 articles published 2000 to 2022 (n = 46 studies) Evidence C source
  Higher mercury and other contaminant biomarkers with shellfish intake; iodine status associated; preterm birth not associated; several studies report lower birth weight
• A worker who handled king and queen scallops for 5 years developed occupational asthma and urticaria with specific IgE to both species and some cross-reactivity to prawn and crab, the only scallop-specific allergy report in the corpus. — One 40-year-old woman in a UK shellfish-processing plant (n = 1) Evidence D source
  OASYS serial peak flow consistent with occupational asthma; RAST positive to queen and king scallop; cross-reactivity with prawns and crabs

The bottom line

Cook them through. Bivalves filter seawater and concentrate norovirus in the process, and a review of 18 years of outbreaks found that the virus survives depuration and the usual kitchen steps, which is why raw or lightly cooked bivalves keep turning up as the source. Steaming costs some nutrients on the way. In the USDA retention table, shellfish out of the shell keep about 90 percent of their vitamin B12, potassium and iron and about 75 percent of their folate and phosphorus. A portion is smaller than it looks on the menu. One cooked scallop weighs about 15 g, so a plate of five or six sea scallops is 75 to 90 g, close to the 85 g the USDA table assumes when nobody says how many. The FDA and EPA put scallop in their Best Choices group, the lowest in mercury, and tell pregnant and breastfeeding women to eat 2 to 3 servings of 4 ounces a week from that list. Set against that is a scoping review of 46 studies on shellfish in pregnancy and the first two years, which found higher contaminant biomarkers, mercury above all, no link with preterm birth, mixed results for birth weight and no data on child development. Both are true at once. The review covers shellfish as a group, so how much of it applies to scallops is unknown. In healthy Norwegian adults aged 48 to 76, a kilogram of fish and mussels a week for 26 weeks raised blood mercury by 5.1 ng/ml, arsenic by 7.1 and lead by 2.6, and the authors judged only the lead worth concern. Again, mussels and fish, and a kilogram a week is a lot. On diabetes the news is dull in a good way. A pooled analysis of 28 cohorts and 956,122 people, with shellfish among the categories analysed but no shellfish figure reported, found no association with type 2 diabetes in men and a 2 percent higher rate per 100 g a week of total fish in women. Allergy is the one place where scallops earn their own warning. Challenge-verified shellfish allergy is rare, 0.1 percent across 93 European studies and no higher than 0.9 percent worldwide, but questionnaires put it as high as 10.3 percent and it may be more common in Southeast Asia. Those prevalence figures pool crustaceans with molluscs and do not separate scallops. In a Shanghai hospital series, lobster or scallop specific IgE was positive in 5.27 percent of children aged 0 to 3. If you react to shrimp, treat scallops with the same care. In one 14-year-old girl the same 38 kDa protein, tropomyosin, bound IgE from shrimp, crab and scallop, and she reacted to scallops only after exercise. That report and one case of occupational asthma in a scallop-processing worker are the whole scallop-specific allergy literature in our corpus. What we could not find matters as much. There is no study of how well anything in a scallop is absorbed, no health claim on scallops in the US or EU registers, no drug interaction entry, and no study under scallop of cadmium or shellfish toxins. If you have a shellfish allergy, are pregnant or have a reason to watch mercury, the missing pieces are the ones that would answer your question, and this page cannot.

Sources

1. scal-c3-12 · reference dataset
   USDA Foundation Scallops, sea, frozen, wild caught — Selenium 15.74 µg (9.71–29.6, n=6) · Protein 13.51 g (9.31–16.25) · Water 82.54 g || Scallops, bay, Patagonian, frozen, wild caught — Selenium 28.37 µg (14.4–36.6, n=6) · Protein 16.39 g · Water 79.43 g || CoFID 16-262 Scallops, steamed — 118 kcal · Protein 23.2 g · Water 73.1 g · Selenium 51 µg · Vitamin B12 9.0 µg · Iodine 20 µg || USDA-RETN-R6:2770 SHELLFISH,WO/SHELL,STEAMED — vitamin_b12_ug 90% · folate_total_ug 75% · phosphorus_mg 75% · potassium_mg 90% · iron_mg 90%
   USDA FoodData Central Foundation Foods, release 2026-04-30, FDC 2747667; CoFID 2021, Public Health England / OGL v3.0; USDA Table of Nutrient Retention Factors R6 (2007) · checked 2026-09-23
2. scal-c3-11 · agency advice
   Eat 2 to 3 servings a week from the "Best Choices" list...1 serving is 4 ounces
   FDA and EPA, Advice about Eating Fish, fda.gov · checked 2026-09-23
3. scal-c3-13 · reference dataset
   FNDDS 2706358 Scallops, steamed or boiled — 1 scallop 15 g · 1 cup 135 g · Quantity not specified 85 g
   USDA FNDDS 2021-2023, Scallops, steamed or boiled, fdc_id 2706358 · checked 2026-09-23
4. scal-c3-10 · review
   Bivalve molluscs, which accumulate noroviruses via filter feeding and are often eaten raw or insufficiently cooked, are a common food vehicle implicated in gastroenteritis outbreaks...The authors describe how their physiology of filter feeding can render them concentrated vehicles of norovirus contamination in polluted environments and how high viral loads persist in molluscs even after application of depuration practices and typical food preparation steps.
   Transbound Emerg Dis, 2020 · checked 2026-09-23
5. scal-c3-01 · RCT
   Of 168 individuals screened, 68 eligible participants were randomly assigned (1:1) to receive either sPls (1 mg/day) or placebo for 12 weeks...After 12 weeks, standardized verbal memory scores were significantly higher in the sPls group than in the placebo group (estimated marginal mean difference, 10.1; 95% confidence interval, 0.4-19.9; p = 0.042).
   Front Nutr, 2026 · checked 2026-09-23
6. scal-c3-03 · meta-analysis of cohort studies
   Incidence rate ratios (IRRs) for associations of total fish, shellfish, fatty, lean, fried, freshwater, and saltwater fish intake and type 2 diabetes were derived for each study...In women, for each 100 g/week higher intake the IRRs (95% CIs) of type 2 diabetes were 1.02 (1.01-1.03, I2 = 61%) for total fish, 1.04 (1.01-1.07, I2 = 46%) for fatty fish, and 1.02 (1.00-1.04, I2 = 33%) for lean fish. In men, all associations were null.
   Nutrients, 2021 · checked 2026-09-23
7. scal-c3-02 · RCT
   We randomly assigned 102 healthy men and women (all non-smokers) aged 48-76 years to an intervention group (n = 51) or a control group (n = 51). Intervention participants received a high amount of fish and mussels for 26 weeks (1 kg week(-1))...The difference in mean change for intervention compared with control persons was 5.1 ng ml(-1) (95% confidence interval (CI) = 4.4, 5.8) for mercury, 7.1 ng ml(-1) (95% CI = 5.0, 9.2) for arsenic, and 2.6 ng ml(-1) (95% CI = 0.0, 5.2) for lead.
   Food Addit Contam Part A Chem Anal Control Expo Risk Assess, 2015 · checked 2026-09-23
8. scal-c3-08 · case report
   Immunoblotting revealed that her serum IgE reacted with the 38 kDa bands for shrimp, crab and scallops, suggesting that tropomyosin was the major allergen. Dot-blot inhibition analysis showed a cross-reactivity among shrimp, crab and scallops.
   J Dermatol, 2006 · checked 2026-09-23
9. scal-c3-04 · meta-analysis of prevalence studies
   fish (1.4%, 0.8-2.0) and shellfish (0.4%, 0.3-0.6). The point prevalence of food challenge-verified allergy were as follows: cow's milk (0.3%, 0.1-0.5), egg (0.8%, 0.5-1.2), wheat (0.1%, 0.01-0.2), soy (0.3%, 0.1-0.4), peanut (0.1%, 0.0-0.2), tree nuts (0.04%, 0.02-0.1), fish (0.02%, 0.0-0.1) and shellfish (0.1%, 0.0-0.2).
   Allergy, 2023 · checked 2026-09-23
10. scal-c3-05 · systematic review of observational studies
    The prevalence of fish allergy ranged from 0% to 7% and the prevalence of shellfish allergy from 0% to 10.3%, depending on the method of diagnosis. Where food challenges were used, the prevalence for fish allergy was found to be 0% to 0.3% and for shellfish allergy was 0% to 0.9%...The limited data available suggest that fish allergy prevalence is similar worldwide; however, shellfish allergy prevalence may be higher in the Southeast Asia region.
    Ann Allergy Asthma Immunol, 2016 · checked 2026-09-23
11. scal-c3-07 · retrospective cohort
    A total of 127 310 tests were included...The positive rates of inhalant allergen such as Ambrosia elatior (1.59%) and food allergens such as egg white (17.36%), milk (30.48%), shrimp (8.27%), crab (8.13%), codfish (2.61%), salmon (0.66%), mytilus edulis (2.89%), lobster/scallop (5.27%), cashew nuts (5.09%), peanuts (3.54%), and soybean (1.73%) were highest at the age of 0-3
    Zhonghua Yu Fang Yi Xue Za Zhi, 2025 · checked 2026-09-23
12. scal-c3-06 · scoping review
    A total of forty-six articles were included in this review. Overall, shellfish consumption was associated with higher biomarkers of environmental contaminants, with mercury being the most studied and having the strongest evidence base...Preterm birth was not associated with shellfish consumption, but newborn anthropometry showed mixed results, with several studies reporting lower birth weight with higher shellfish consumption.
    Nutr Res Rev, 2025 · checked 2026-09-23
13. scal-c3-09 · case report
    A 40-year-old female worked in a shellfish-processing plant, handling king and queen scallops for 5 years...RAST testing demonstrated evidence of specific sensitization (IgE) to queen and king scallop. There was also some cross-reactivity observed with other shellfish (prawns and crabs).
    Occup Med (Lond), 2006 · checked 2026-09-23