Functional Foods · Fish
Oily Fish
Several species (for example Salmo salar, Sardina pilchardus, Scomber scombrus, Clupea harengus) · also called Fatty fish, pescado azul
Oily fish, such as salmon, sardines, mackerel and herring, have more oil in their flesh than white fish and are the richest food source of omega-3 fats. People who eat more fish had fewer heart events and slightly fewer deaths in large studies, but those studies cannot prove cause, and the trials that exist are mostly of capsules. The main cautions are fish allergy, mercury and pollutants (with set limits for pregnancy and girls), and raw or cold-smoked fish in pregnancy.
General information, not medical advice. Last substantive update · Not medically reviewed. A named clinician has not signed off on this page. How this page is made
About Oily Fish
Oily fish are fish with more oil in the flesh, such as salmon, sardines, mackerel, herring and trout. They are a food, not a proven remedy. People who eat more fish do better on several measures in large observational studies, but trials that could show cause are mostly of omega-3 capsules.
What it is
Oily (fatty) fish have more oil in their flesh than white fish. The NHS lists herring (including bloater, kipper and hilsa), pilchards, salmon, sardines, sprats, trout and mackerel, and says fresh and canned tuna do not count. It describes oily fish as high in long-chain omega-3 fats and a good source of vitamin D. The FDA adds iron, iodine, choline, vitamin B12 and selenium to the nutrients fish provide.
Names can hide differences. In the FDA and EPA mercury chart, Atlantic mackerel and Pacific chub mackerel are Best Choices, Spanish mackerel is a Good Choice and king mackerel is a Choice to Avoid. Canned sardines, pilchards and tinned salmon have bones you can eat (NHS).
Nutrition, and what could not be checked
No per-portion table (USDA) was available for this page, so it does not state calories, protein or the grams of omega-3 in a portion. Amounts of omega-3 and vitamin D differ by species, by farmed or wild, and by fresh or canned, so the label on tinned fish is the best guide.
Official portion sizes are used in the safety advice: the NHS counts a portion as about 140 g cooked, and the FDA counts a serving as about 4 ounces, roughly the palm of the hand.
What the research shows
Nearly all the human evidence on eating fish is observational. A 2021 review of 24 studies (714,526 people) found non-fried fish was probably linked with lower risk of heart events and heart attack, and fried fish with higher risk. A 2016 pooled analysis of 12 cohorts found the highest fish intake went with about 6% lower risk of death from any cause. A 2024 pooled analysis of 35 studies linked higher fish intake with lower risk of cognitive impairment and dementia. A 2021 analysis of 28 cohorts found no link with type 2 diabetes in men and a slightly higher risk in women.
Trials are scarce. The 2020 Cochrane review of 86 trials (162,796 people) found little or no effect of omega-3 on deaths, heart events or stroke, but nearly all tested capsules, and the authors say there is little evidence of effects of eating fish. One small trial showed two fish meals a week raise the omega-3 index. One trial in 199 school-age children gave mixed results.
These studies can show a link, not cause. People who eat more fish may also differ in income, diet and habits.
Fish versus fish oil capsules
Fish is a whole food with protein, vitamin D and other nutrients. Capsules and cod liver oil are different products. In one small trial, two fish meals a week and a daily omega-3 capsule each raised the omega-3 index, but the trial did not test heart attacks or deaths. The big Cochrane review is mostly of capsules. A result for a capsule does not carry over to a meal of fish, and the reverse is also true. The NHS also warns that fish liver oil supplements are high in vitamin A and should be avoided in pregnancy.
At a glance
Traditional uses history, not proof
- Eaten as food in many places
- Long use as food is not proof that it treats any condition
Studied for research
- Omega-3 fats and vitamin D, moderate certainty that oily fish supply them (no nutrient table read)
- Heart disease, low certainty (observational; fried fish went the other way)
- Death from any cause, low certainty (observational)
- Trials of eating fish, insufficient (the large Cochrane review is mostly capsules)
- Baby's brain development in pregnancy, low certainty (observational)
- Memory and dementia, low certainty (observational)
- Children's thinking, low certainty (one trial)
- Type 2 diabetes, mixed (no benefit seen; slight rise in women)
Main compounds
- EPA and DHA (long-chain omega-3 fats)
- Vitamin D
- Methylmercury (a contaminant)
Common forms
- Fresh, frozen, canned, smoked or cured oily fish as food
- Steamed, baked or grilled versus fried (the NHS and a 2021 review favour non-fried)
- Fish oil and cod liver oil capsules are different products and are not covered here
Research links: 2021 review: fish and heart disease (24 studies) · 2020 Cochrane review: omega-3 and heart disease (86 trials) · FDA and EPA advice about eating fish · Research Library · Genes & Biomarkers Library
What it is and its history
- Accepted scientific name
- Not a single species. "Oily fish" is a food group.
- Naming authority
- The NHS list is the group used on this page; the FDA/EPA list names species separately.
- Common names
- Oily fish (English); Fatty fish (English); Pescado azul (Spanish); Pescado graso (Spanish)
- Family or group
- Several fish families. Oily fish are grouped by how much oil is in the flesh, not by biology.
- Classification
- Animalia > Several: Salmonidae (salmon, trout), Clupeidae (herring, sardines, pilchards, sprats), Scombridae (mackerel), per GBIF for the species checked
- Native range
- Not verified from a source read.
- Habitat
- Not verified from a source read.
- Cultivation
- Not verified from a source read.
- Harvest and processing
- Not read, except that frying can increase the fat content of fish (NHS), that fish may be sold fresh, frozen, canned, smoked or cured (cold-smoked and cured fish carry a listeria warning in pregnancy), and that canned and fresh were not compared in the studies read.
- Look-alikes and adulterants
- Name: Tuna; Note: The NHS says fresh and canned tuna do not count as oily fish. It has its own mercury limits.; Name: White fish (cod, haddock, pollock); Note: Low in fat; a different group from oily fish (NHS).; Name: King mackerel versus Atlantic mackerel; Note: Both are called mackerel, but the FDA/EPA chart puts Atlantic and Pacific chub mackerel on Best Choices and king mackerel on Choices to Avoid.; Name: Fish oil and cod liver oil capsules; Note: Supplements, not the food. See the linked page on cod liver oil and fish oil from food.
- Sustainability and conservation
- Not assessed. The NHS notes that eating a variety of fish helps protect stocks, but no stock assessment was read.
What is inside, and how it may work
What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.
Main compounds
| Compound | Family | Where it is concentrated | Activity studied | Level of evidence |
|---|---|---|---|---|
| EPA and DHA (long-chain omega-3 fatty acids) | fatty acids | Flesh of oily fish Not read; the NHS says oily fish are the richest food source and are "high" in long-chain omega-3. | Raised the omega-3 index in a small trial when eaten as two fish meals a week. Long-chain omega-3 capsules lowered triglycerides about 15% in pooled trials. 16 4 1 | Human data |
| Vitamin D | vitamin | Flesh of oily fish Not read; the NHS calls oily fish a good source. | Not studied in the sources read for this food. 16 | Human data |
| Methylmercury | contaminant | Larger, longer-lived fish Not read as numbers; the FDA/EPA chart ranks species. | Toxic to the developing nervous system (WHO). 18 10 | Human data |
Mechanisms, receptors and pathways
| Target or pathway | Gene or receptor | What was found | Level |
|---|---|---|---|
| Red blood cell omega-3 level | Not specified in the sources read | In the YouFish trial, two fish meals a week raised the omega-3 index and lowered the omega-6 share in red blood cell membranes. This is a marker of intake, not a proven reason for any health effect. 4 | Human data |
Absorption, metabolism and elimination
- Absorption
- Not found for oily fish in the sources read.
- Distribution
- Not found.
- Metabolism
- Not found.
- Elimination
- Not found.
- Bioavailability
- Not established; the trial shows blood levels rise after weeks of fish meals.
Isolated compounds versus whole extracts
The observational results (heart, death, dementia, diabetes, pregnancy) are for fish eaten as food. The Cochrane review of 86 trials is mostly of omega-3 capsules, and its authors say there is little evidence of effects of eating fish. In the one trial that compared them, fish meals and a capsule each raised the omega-3 index, but heart outcomes were not tested.
Nutritional composition
Per-portion nutrition numbers are NOT given on this page. USDA FoodData Central could not be queried today (the public key was rate-limited) and no other table was read. What was read: the NHS says oily fish are high in long-chain omega-3 fats and a good source of vitamin D, that a portion is about 140 g cooked, and that canned sardines, pilchards and tinned salmon have edible bones that add calcium and phosphorus; the FDA says fish provide omega-3 (DHA and EPA), iron, iodine, choline, protein, vitamin B12, vitamin D and selenium, and counts a serving as about 4 ounces (the palm of the hand). Species, farming, season and canning change the amounts, so check the nutrition label on tinned fish.
1 moderate certainty1 mixed findings5 low certainty1 not enough evidence
What was looked at
The 8 benefits and uses checked for Oily Fish, each with how strong the evidence is. Tap one to open it.
- Omega-3 fats and vitamin D (what the food provides)Moderate certainty
- Heart disease and heart attack (observational)Low certainty
- Living longer (death from any cause, observational)Low certainty
- Trials of eating fish for heart outcomesNot enough evidence
- Baby's brain development when fish is eaten in pregnancy (observational)Low certainty
- Memory, thinking and dementia in older age (observational)Low certainty
- Thinking and behaviour in school-age children (one trial)Low certainty
- Type 2 diabetes risk (observational, mixed)Mixed findings
Lab markers tracked in the studies
Omega-3 index (EPA and DHA in red blood cells)Blood fats and hs-CRP (an inflammation marker)Triglycerides (a blood fat), from omega-3 supplement trialsAttention and mental flexibility test scores (children)
What is Oily Fish good for?
The main studied uses and how strong the human evidence is for each. Almost all of it comes from studies that watch what people eat, which can show a link but not prove cause.
Benefits, one by one
Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.
Omega-3 fats and vitamin D (what the food provides)
Moderate certaintyThe NHS says oily fish are high in long-chain omega-3 fats and a good source of vitamin D, and the FDA lists omega-3 (DHA and EPA), iron, iodine, choline, vitamin B12, vitamin D and selenium among the nutrients in fish. No portion-by-portion numbers were read for this page.
2 studiesOily fish as food (salmon, sardines, mackerel, herring, trout). Canne…
Studies, doses and limits
What the trials found
Statements from the NHS and the FDA/EPA. No trial was read that tested whether eating oily fish corrects a low nutrient level, apart from the omega-3 index trial under Biomarkers.
Results
Oily fish are named by UK and US agencies as a source of long-chain omega-3 fats. Amounts differ by species, farming and canning, and were not read.
Effect sizes as reported
No numbers read. USDA portion data could not be retrieved for this page.
Why this rating
Moderate that oily fish supply these nutrients, because two agencies say so, but no nutrient table was read, so amounts are unverified.
Form and dose studied
Oily fish as food (salmon, sardines, mackerel, herring, trout). Canned and fresh were not compared.
Who was studied
General population.
Limits
Statements, not a nutrient table. Species, season, farming and canning change the amounts.
Why researchers looked
Oily fish are the richest food source of the long-chain omega-3 fats EPA and DHA, so most research on fish asks about those fats.
Traditional use
Fish has been eaten as food in many places. Long use as food is not proof that it treats any condition.
Proposed mechanism Authoritative guidance
Not shown for the whole food. EPA and DHA are the long-chain omega-3 fats the health agencies point to.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab for fish allergy, mercury and pregnancy limits.
Heart disease and heart attack (observational)
Low certaintyIn studies that followed large groups of people, those who ate more non-fried fish had fewer heart events. Fried fish went the other way. This shows a link, not cause.
2 studiesFish eaten as food. Fried and non-fried were separated; species were …
Studies, doses and limits
What the trials found
A 2021 systematic review of 24 observational studies (714,526 people) found non-fried fish was probably linked with lower risk of cardiovascular disease events and heart attack. Fried fish was probably linked with higher risk of both. No study showed a significant link with stroke. The FDA says strong evidence shows eating fish as part of a healthy eating pattern may have heart health benefits.
Results
A probable link to lower risk for non-fried fish, a probable link to higher risk for fried fish, and nothing clear for stroke.
Effect sizes as reported
No numbers in the abstract.
Why this rating
Low: observational studies, and the review itself starts by saying earlier results were inconsistent. The FDA statement is about a whole healthy eating pattern, not fish alone.
Form and dose studied
Fish eaten as food. Fried and non-fried were separated; species were not.
Who was studied
Adults in several countries.
Limits
People who eat fish may also differ in other ways. The abstract does not say what fish replaced in the diet.
Why researchers looked
Fish is the best-known food source of omega-3 fats, and heart health is the oldest question asked about it.
Traditional use
Not described in the sources read.
Proposed mechanism Hypothesis
Not shown. The omega-3 fats are one idea; the reviewers do not test it.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab.
Living longer (death from any cause, observational)
Low certaintyPeople who ate the most fish had about 6% lower risk of dying from any cause than people who ate the least, in a pooled analysis of 12 cohorts.
1 studiesAll fish eaten as food, not only oily fish.
Studies, doses and limits
What the trials found
A 2016 meta-analysis of 12 prospective cohorts (672,389 people, 57,641 deaths) found the highest fish intake group had about 6% lower all-cause death risk (RR 0.94, 95% CI 0.90 to 0.98). The link was not a straight line: 60 g of fish a day versus none went with 12% lower risk (RR 0.88, 0.83 to 0.93).
Results
A small link to lower all-cause death, from cohorts that ended in 2014 or earlier.
Effect sizes as reported
RR 0.94 (0.90 to 0.98); 60 g/day vs never RR 0.88 (0.83 to 0.93).
Why this rating
Low: observational, small effect, all fish combined.
Form and dose studied
All fish eaten as food, not only oily fish.
Who was studied
Adults in prospective cohorts.
Limits
Cannot show that fish caused the difference. Fish eaters may differ in income, diet and habits.
Why researchers looked
If a food helps many body systems, it might show up as fewer deaths overall.
Traditional use
Not described in the sources read.
Proposed mechanism Unknown
Not shown.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab.
Trials of eating fish for heart outcomes
Not enough evidenceThe big Cochrane review of omega-3 trials found little or no effect on deaths or heart events, and says there is little evidence of effects of eating fish. Almost all of those trials used capsules.
1 studiesMostly omega-3 capsules. Not oily fish meals.
Studies, doses and limits
What the trials found
The 2020 Cochrane review included 86 randomised trials (162,796 people, 12 to 88 months). Most tested capsules; some used omega-3-rich foods or dietary advice. More long-chain omega-3 made little or no difference to all-cause death (RR 0.97, 95% CI 0.93 to 1.01; high certainty), cardiovascular events (RR 0.96, 0.92 to 1.01; high) or stroke (RR 1.02, 0.94 to 1.12; moderate). It may slightly reduce coronary heart disease events (RR 0.91, 0.85 to 0.97; low certainty). The authors say there is little evidence of effects of eating fish.
Results
No trial of oily fish meals with heart attacks or deaths as the outcome was read. The capsule trials do not show a large effect.
Effect sizes as reported
All-cause death RR 0.97; coronary heart disease events RR 0.91.
Why this rating
Insufficient for oily fish as food: the trials are mostly of capsules. For capsules the main results are high-certainty null results.
Form and dose studied
Mostly omega-3 capsules. Not oily fish meals.
Who was studied
Adults at varying heart risk, mainly in high-income countries.
Limits
A result for a capsule does not carry over to a meal of fish, and the reverse is also true.
Why researchers looked
Observational links need trials to test cause, and trials of omega-3 are the nearest test.
Proposed mechanism Not applicable
Not applicable.
A proposed mechanism does not show that the effect happens in people.
Fish oil capsules are a different product; see the linked cod liver oil and fish oil page.
Baby's brain development when fish is eaten in pregnancy (observational)
Low certaintyA 2015 review of 8 studies concluded that moderate fish intake in pregnancy gave benefits that outweigh possible harms for the child's brain development, if the fish is low in mercury.
2 studiesFish and seafood in general, not oily fish alone.
Studies, doses and limits
What the trials found
The review included 8 studies of healthy pregnant women (from 279 papers screened) and described them rather than pooling, because they differed too much. The FDA says moderate scientific evidence shows fish in pregnancy can help a baby's cognitive development.
Results
A benefit that outweighs harms for moderate intake of low-mercury fish. Nothing here supports eating high-mercury fish.
Effect sizes as reported
No numbers in the abstract.
Why this rating
Low: eight observational studies with mixed methods and outcomes; the review is from 2015. The FDA rates the evidence moderate.
Form and dose studied
Fish and seafood in general, not oily fish alone.
Who was studied
Healthy pregnant women and their children.
Limits
Observational, small number of studies, search ended in 2014.
Why researchers looked
Fish provides omega-3 fats, iodine, iron and choline that matter for a baby's brain, but fish can also carry mercury.
Traditional use
Not described in the sources read.
Proposed mechanism Authoritative guidance
Not shown. The FDA lists omega-3 (DHA and EPA), iron, iodine and choline as nutrients in fish that support brain development.
A proposed mechanism does not show that the effect happens in people.
Pregnancy has fish limits and food-safety rules. See the Safety tab.
Memory, thinking and dementia in older age (observational)
Low certaintyPeople who ate the most fish had a lower likelihood of cognitive impairment or decline and of dementia (RR 0.82 for each) than people who ate the least, in a 2024 pooled analysis. This is a link, not proof.
1 studiesAll fish eaten as food.
Studies, doses and limits
What the trials found
A 2024 meta-analysis of 35 observational studies found, for the highest versus lowest fish intake, RR 0.82 (95% CI 0.75 to 0.90) for cognitive impairment or decline, RR 0.82 (0.73 to 0.93) for dementia and RR 0.80 (0.67 to 0.96) for Alzheimer disease. At 150 g of fish a day versus none, RR was 0.70 (0.52 to 0.95) for cognitive impairment or decline. For dementia and Alzheimer disease the authors say more studies are needed to improve the strength of evidence.
Results
A consistent small-to-moderate link to lower risk in observational studies. No trial of fish for dementia was read.
Effect sizes as reported
RR 0.82 (cognitive impairment/decline); 0.82 (dementia); 0.80 (Alzheimer disease).
Why this rating
Low: observational only; the authors themselves call for more studies on dementia.
Form and dose studied
All fish eaten as food.
Who was studied
Adults, mostly older.
Limits
Fish eaters may differ in education, diet and health. Some results varied between studies (I2 up to 61%).
Why researchers looked
DHA is a major fat in the brain, so fish has long been studied for memory and dementia.
Traditional use
Not described in the sources read.
Proposed mechanism Hypothesis
Not shown.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab.
Thinking and behaviour in school-age children (one trial)
Low certaintyIn one 12-week trial of 199 children aged 8 to 9, oily fish improved parts of a thinking test and slightly reduced parent-rated difficulties compared with poultry, but the main overall thinking score was not clearly better.
1 studiesOily fish as food, compared with poultry.
Studies, doses and limits
What the trials found
The FiSK Junior trial gave 199 healthy children about 300 g a week of oily fish or poultry for 12 weeks (the fish group ate about 375 g a week). The overall cognitive score tended to improve by 0.17 points (95% CI -0.01 to 0.35). Attention errors fell by 1.9 (-3.4 to -0.3), reaction time in a complex task improved by 51 ms (-94 to -7), and the parent-rated difficulties score fell by 0.89 (-1.60 to -0.18).
Results
A small, mixed result: some measures improved, the overall score did not clearly.
Effect sizes as reported
Overall score +0.17 (-0.01 to 0.35); attention errors -1.9; difficulties -0.89.
Why this rating
Low: one trial, short, a main score that did not clearly differ, and parent-reported behaviour.
Form and dose studied
Oily fish as food, compared with poultry.
Who was studied
Healthy children aged 8 to 9.
Limits
One country, 12 weeks, results not repeated in another trial that was read.
Why researchers looked
Omega-3 fats build up in the brain during childhood.
Traditional use
Not described in the sources read.
Proposed mechanism Hypothesis
Not shown. The authors link the results to higher red blood cell omega-3, which rose by 2.3 points.
A proposed mechanism does not show that the effect happens in people.
Children have mercury and pollutant limits; see the Safety tab.
Type 2 diabetes risk (observational, mixed)
Mixed findingsA large pooled analysis found no link between fish intake and type 2 diabetes in men, and a slightly higher risk in women, mainly in the Americas. This does not show that fish causes diabetes.
1 studiesFish eaten as food, split by type.
Studies, doses and limits
What the trials found
A 2021 pooled analysis of 28 cohorts (956,122 people, 48,084 new cases) found that in women each extra 100 g a week was linked with IRR 1.02 (1.01 to 1.03) for total fish and 1.04 (1.01 to 1.07) for fatty fish. In men all links were null. Results in women varied by region.
Results
No benefit seen, and a small positive link in women. The authors call it neutral in men and modest in women.
Effect sizes as reported
Women per 100 g/week: fatty fish IRR 1.04; total fish 1.02. Men: no link.
Why this rating
Mixed: no benefit and a small possible increase, with large differences between studies and regions.
Form and dose studied
Fish eaten as food, split by type.
Who was studied
Adults in 28 cohorts in the Americas, Europe, Western Pacific and Eastern Mediterranean.
Limits
Observational. Cooking, side foods and pollutants were not examined.
Why researchers looked
Omega-3 fats and diet quality are linked to blood sugar, so the question is whether fish eaters get less diabetes.
Traditional use
Not described in the sources read.
Proposed mechanism Hypothesis
Not shown. The authors suggest cooking methods, side foods and pollutants should be studied.
A proposed mechanism does not show that the effect happens in people.
None specific.
Connections to the rest of health
How Oily Fish connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.
Explore every connection: goals, body systems, organs, symptoms, genes
A. Wellness goals
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Preventive Wellness | Moderate certainty | Omega-3 fats and vitamin D (what the food provides): The NHS says oily fish are high in long-chain omega-3 fats and a good source of vitamin D, and the FDA lists omega-3 (DHA and EPA), iron, iodine, choline, vitamin B12, vitamin D and selenium among the nutrients in fish. No portion-by-portion numbers were read for this page. | 16 10 | |
| Heart Health | Moderate certainty | Omega-3 fats and vitamin D (what the food provides): The NHS says oily fish are high in long-chain omega-3 fats and a good source of vitamin D, and the FDA lists omega-3 (DHA and EPA), iron, iodine, choline, vitamin B12, vitamin D and selenium among the nutrients in fish. No portion-by-portion numbers were read for this page. | 16 10 | |
| Heart Health | Low certainty | Heart disease and heart attack (observational): In studies that followed large groups of people, those who ate more non-fried fish had fewer heart events. Fried fish went the other way. This shows a link, not cause. | 3 10 | |
| Healthy Aging | Low certainty | Living longer (death from any cause, observational): People who ate the most fish had about 6% lower risk of dying from any cause than people who ate the least, in a pooled analysis of 12 cohorts. Memory, thinking and dementia in older age (observational): People who ate the most fish had a lower likelihood of cognitive impairment or decline and of dementia (RR 0.82 for each) than people who ate the least, in a 2024 pooled analysis. This is a link, not proof. | 8 2 | |
| Heart Health | Not enough evidence | Trials of eating fish for heart outcomes: The big Cochrane review of omega-3 trials found little or no effect on deaths or heart events, and says there is little evidence of effects of eating fish. Almost all of those trials used capsules. | 1 | |
| Womens Wellness | Low certainty | Baby's brain development when fish is eaten in pregnancy (observational): A 2015 review of 8 studies concluded that moderate fish intake in pregnancy gave benefits that outweigh possible harms for the child's brain development, if the fish is low in mercury. | 6 10 | |
| Pregnancy Support | Low certainty | Baby's brain development when fish is eaten in pregnancy (observational): A 2015 review of 8 studies concluded that moderate fish intake in pregnancy gave benefits that outweigh possible harms for the child's brain development, if the fish is low in mercury. | 6 10 | |
| Focus Memory | Low certainty | Memory, thinking and dementia in older age (observational): People who ate the most fish had a lower likelihood of cognitive impairment or decline and of dementia (RR 0.82 for each) than people who ate the least, in a 2024 pooled analysis. This is a link, not proof. | 2 | |
| Focus Memory | Low certainty | Thinking and behaviour in school-age children (one trial): In one 12-week trial of 199 children aged 8 to 9, oily fish improved parts of a thinking test and slightly reduced parent-rated difficulties compared with poultry, but the main overall thinking score was not clearly better. | 7 | |
| Child Wellness | Low certainty | Thinking and behaviour in school-age children (one trial): In one 12-week trial of 199 children aged 8 to 9, oily fish improved parts of a thinking test and slightly reduced parent-rated difficulties compared with poultry, but the main overall thinking score was not clearly better. | 7 | |
| Blood Sugar Balance | Mixed findings | Type 2 diabetes risk (observational, mixed): A large pooled analysis found no link between fish intake and type 2 diabetes in men, and a slightly higher risk in women, mainly in the Americas. This does not show that fish causes diabetes. | 5 |
B. Body systems
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Cardiovascular System | Biological association | Moderate certainty | Studied for: Omega-3 fats and vitamin D (what the food provides) Studied for: Heart disease and heart attack (observational) | 16 10 3 1 |
| Whole Body | Biological association | Low certainty | Studied for: Living longer (death from any cause, observational) | 8 |
| Nervous System | Biological association | Low certainty | Studied for: Baby's brain development when fish is eaten in pregnancy (observational) Studied for: Memory, thinking and dementia in older age (observational) | 6 10 2 7 |
| Endocrine System | Biological association | Mixed findings | Studied for: Type 2 diabetes risk (observational, mixed) | 5 |
E. Health conditions
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Food allergy | Adverse effect or risk | Documented risk | Fish is a major food allergen in the US list and among the most common food allergies in older children and adults. Fish is a major food allergen and among the most common food allergies in older children and adults. Preparation or compound: Fish protein, eaten as food |
9 15 |
| Heart disease | Observational | Non-fried fish was probably linked with fewer heart events in observational studies; trials are mostly of capsules. Preparation or compound: Non-fried fish as food |
3 1 |
I. Biomarkers
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Omega-3 index (EPA and DHA in red blood cells) | Biological association | Low certainty | Measured in trials: raised. A lab change is not the same as a health benefit. | 4 |
| Blood fats and hs-CRP (an inflammation marker) | Biological association | Low certainty | Measured in trials: no significant change. A lab change is not the same as a health benefit. | 4 |
| Triglycerides (a blood fat), from omega-3 supplement trials | Biological association | Not enough evidence | Measured in trials: lowered. A lab change is not the same as a health benefit. | 1 |
| Attention and mental flexibility test scores (children) | Biological association | Low certainty | Measured in trials: improved. A lab change is not the same as a health benefit. | 7 |
K. Biological pathways
L. Active compounds
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Mercury (methylmercury) | Documented risk | Mercury builds up in fish; agency lists sort species by level. Preparation or compound: Fish, mainly large predatory species |
18 10 | |
| EPA and DHA (long-chain omega-3 fatty acids) | Biological association | Human | Raised the omega-3 index in a small trial when eaten as two fish meals a week. Long-chain omega-3 capsules lowered triglycerides about 15% in pooled trials. Preparation or compound: Flesh of oily fish |
16 4 1 |
| Vitamin D | Biological association | Human | Not studied in the sources read for this food. Preparation or compound: Flesh of oily fish |
16 |
| Methylmercury | Biological association | Human | Toxic to the developing nervous system (WHO). Preparation or compound: Larger, longer-lived fish |
18 10 |
Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).
The evidence
The research centre for Oily Fish. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.
Evidence by outcome
Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).
How we rate evidence
High certainty
Several well-run trials or reviews agree; further research is unlikely to change the picture much.
Moderate certainty
Good trials point the same way, but some doubt remains.
Low certainty
Small, short or inconsistent trials. The finding could change with better research.
Very low certainty
Very little or very weak human data. Treat as a possibility only.
Mixed findings
Trials or reviews disagree with each other.
Not enough evidence
Not enough human research to say either way.
Evidence against
Good research found no benefit, or found harm.
We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We started from our earlier oily fish page, then re-read the NHS, FDA, EPA, MedlinePlus and WHO pages and the PubMed abstracts for every study cited, and added studies on dementia, children and type 2 diabetes. Only abstracts were read for studies. Items we could not verify are flagged in the research gaps.
Study library: every study we checked 18
| Study | Design | People | Product, dose, length | Result |
|---|---|---|---|---|
| Abdelhamid 2020 Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev · PMID 32114706 · DOI |
Systematic review meta analysis |
162796 86 randomised trials, 162,796 adults, 12 to 88 months |
Long-chain omega-3 (EPA, DHA) from capsules, enriched foods or dietary advice; also plant omega-3 (ALA) 0.5 g a day to over 5 g a day of long-chain omega-3 12 to 88 months · vs Usual or lower intake |
Most trials used capsules. Little or no effect of more long-chain omega-3 on all-cause death (high certainty), cardiovascular events (high), stroke (moderate) or rhythm problems (low). Possible slight fall in coronary heart disease deaths and events (low certainty) and about 15% lower triglycerides (high certainty). The authors say there is little evidence of effects of eating fish. All-cause mortality RR 0.97; coronary heart disease events RR 0.91; triglycerides about 15% lower (All-cause 0.93 to 1.01; coronary heart disease events 0.85 to 0.97) Methods, limits and fundingOutcomes: Death, cardiovascular events, stroke, rhythm problems, blood lipids Limitations: Mostly capsule trials, so not a test of eating oily fish. Trials were of varying quality (28 of 86 at low risk of bias). Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Godos 2024 Fish consumption, cognitive impairment and dementia: an updated dose-response meta-analysis of observational studies. Aging Clin Exp Res · PMID 39162889 · DOI |
Systematic review meta analysis |
35 observational studies of fish intake and cognitive impairment, dementia and Alzheimer disease | Fish eaten as food (all fish) Highest versus lowest group; dose-response up to 150 g a day Observational · vs Lowest fish intake |
Highest fish intake was linked with lower likelihood of cognitive impairment or decline, dementia and Alzheimer disease. For dementia and Alzheimer disease the authors say more studies are needed to strengthen the evidence. Cognitive impairment/decline RR 0.82; dementia RR 0.82; Alzheimer disease RR 0.80; 150 g/day vs none RR 0.70 for cognitive impairment/decline (0.75 to 0.90; 0.73 to 0.93; 0.67 to 0.96; 0.52 to 0.95) Methods, limits and fundingOutcomes: Cognitive impairment or decline, dementia, Alzheimer disease Limitations: Observational, so people who eat fish may differ in other ways. Moderate differences between studies for some outcomes (I2 up to 61%). All fish combined. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Krittanawong 2021 Fish Consumption and Cardiovascular Health: A Systematic Review. Am J Med · PMID 33444594 · DOI |
Systematic review |
714526 24 observational studies, 714,526 people in several countries |
Fish eaten as food, fried and non-fried Observational, various · vs Lower fish intake |
Non-fried fish was probably linked with lower risk of cardiovascular events and heart attack. Fried fish was probably linked with higher risk of both. No study showed a significant link between fish and stroke. No numbers in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: Cardiovascular disease events, heart attack, stroke Limitations: Observational studies, which show links not cause. The abstract does not break down which fish species were eaten. The abstract opens by saying earlier results were inconsistent. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| McMullan 2025 Influence of Fish Consumption and omega-3 Supplementation on the omega-3 Index of Young Adults: A 2 x 2 Factorial Randomized Controlled Trial (YouFish Study). J Nutr · PMID 41082976 · DOI |
Controlled trial |
40 Healthy adults aged 18 to 30 with low fish intake and omega-3 index under 6% |
Two fish meals a week (one oily, one white), and separately a daily 700 mg EPA+DHA capsule 2 portions a week; capsule 700 mg a day 8 weeks · vs Two non-fish meals a week and a placebo capsule |
Two fish meals a week raised the omega-3 index by about 2.3 percentage points; the capsule raised it by about 2.0. Neither changed blood lipids or hs-CRP significantly. Omega-3 index +2.27% +/- 0.82 (fish), +2.03% +/- 0.88 (capsule) (Not given in the abstract) Methods, limits and fundingOutcomes: Omega-3 index (EPA and DHA in red blood cell membranes), blood lipids, hs-CRP Limitations: Small (40 people), short, healthy young adults. A blood marker, not heart attacks or deaths. Registered NCT06729229. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Pastorino 2021 Heterogeneity of Associations between Total and Types of Fish Intake and the Incidence of Type 2 Diabetes: Federated Meta-Analysis of 28 Prospective Studies Including 956,122 Participants. Nutrients · PMID 33917229 · DOI |
Pooled cohort analysis |
956122 28 prospective cohorts, 956,122 people, 48,084 new cases of type 2 diabetes |
Total fish, fatty fish, lean fish, fried fish and other types, eaten as food Per 100 g a week higher intake Cohort follow-up · vs Lower intake |
In women, each extra 100 g of fatty fish a week was linked with slightly higher type 2 diabetes risk. In men, all links were null. The link in women differed by region and was only seen for total fish in the Americas. The authors call the overall picture neutral in men and a modest positive link in women. Women, per 100 g/week: fatty fish IRR 1.04; total fish 1.02; men null (Fatty fish 1.01 to 1.07; total fish 1.01 to 1.03) Methods, limits and fundingOutcomes: New type 2 diabetes Limitations: Observational. Large differences between studies for total fish (I2 61%). Cooking methods, side foods and pollutants were not examined. Grants listed in the record include UK public funders (Medical Research Council, Cancer Research UK, Wellcome Trust). Funding and conflicts: Public research funders appear in the record; no industry funding was seen in the record. Read: abstract |
| Starling 2015 Fish intake during pregnancy and foetal neurodevelopment--a systematic review of the evidence. Nutrients · PMID 25793632 · DOI |
Systematic review |
8 studies of healthy pregnant women (searched 2000 to March 2014) that measured fish intake and the child's later development | Fish and seafood eaten in pregnancy Observational · vs Lower intake |
The authors concluded that moderate fish intake in pregnancy gave benefits that outweigh possible harms for the child's neurodevelopment, provided the fish is low in mercury. Studies differed too much to pool, so the comparison was descriptive. No numbers in the abstract (Not applicable) Methods, limits and fundingOutcomes: Child neurodevelopment Limitations: Only 8 studies after screening 279 papers, with different methods and outcomes. Observational. Search ended in 2014. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Teisen 2020 Effects of oily fish intake on cognitive and socioemotional function in healthy 8-9-year-old children: the FiSK Junior randomized trial. Am J Clin Nutr · PMID 32529206 · DOI |
Controlled trial |
199 Healthy children aged 8 to 9 (197 finished) |
Oily fish, about 300 g a week targeted (children ate about 375 g a week) About 300 g a week targeted 12 weeks · vs Poultry |
The overall cognitive score only tended to improve (95% CI just crossed zero). Attention errors fell and reaction time in a complex task was faster in the fish group, and parent-rated difficulties fell slightly. Red blood cell omega-3 was 2.3 points higher with fish. Overall cognitive score +0.17 points; attention errors -1.9; mixing cost -51 ms; difficulties score -0.89 (Overall score -0.01 to 0.35; errors -3.4 to -0.3; -94 to -7 ms; -1.60 to -0.18) Methods, limits and fundingOutcomes: Overall cognitive score, attention, cognitive flexibility, parent-rated behaviour Limitations: One trial, 12 weeks, one country. The main overall score was not clearly significant; the clearer results are for parts of it. Parent ratings can be biased because parents could know the diet. Registered NCT02809508. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| Zhao 2016 Fish consumption and all-cause mortality: a meta-analysis of cohort studies. Eur J Clin Nutr · PMID 25969396 · DOI |
Systematic review meta analysis |
672389 12 prospective cohort studies, 672,389 people, 57,641 deaths |
Fish eaten as food (all fish) Highest versus lowest intake group; dose-response also analysed Cohort follow-up · vs Lowest fish intake |
The highest fish intake group had about 6% lower risk of death from any cause. In the dose-response analysis, 60 g of fish a day versus none was linked with 12% lower risk. The link was not a straight line. Highest vs lowest: RR 0.94; 60 g/day vs never: RR 0.88 (Highest vs lowest 0.90 to 0.98 (I2 39.1%); 60 g/day 0.83 to 0.93) Methods, limits and fundingOutcomes: All-cause death Limitations: Observational. All fish combined, so it does not say which fish. Search ended in 2014. Funding and conflicts: Funding is not stated in the abstract. Read: abstract |
| s-fda-allergens US FDA: Food Allergies · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-fda-epa-fish FDA and EPA: Advice about Eating Fish · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-gbif-clupea-harengus GBIF Backbone: Clupea harengus (Atlantic herring) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text | ||
| s-gbif-salmo-salar GBIF Backbone: Salmo salar (Atlantic salmon) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text | ||
| s-gbif-sardina-pilchardus GBIF Backbone: Sardina pilchardus (European pilchard or sardine) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text | ||
| s-gbif-scomber-scombrus GBIF Backbone: Scomber scombrus (Atlantic mackerel) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text | ||
| s-medlineplus-foodallergy MedlinePlus: Food allergy · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nhs-fish NHS: Fish and shellfish · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nhs-pregnancy-avoid NHS: Foods to avoid in pregnancy · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-who-mercury WHO: Mercury and health · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text |
What we do not know yet
- No trial of oily fish meals with heart attack, stroke or death as the outcome was found; the Cochrane review says there is little evidence on eating fish.
- Nearly all the heart, death, dementia and diabetes results are observational and cannot show cause.
- No USDA nutrient table was read, so amounts of omega-3, vitamin D, protein and calories per portion are not given.
- The children's thinking result comes from one trial and the overall score was not clearly better.
- Parasites, histamine in badly kept fish, farmed versus wild, canned and smoked differences, medicine interactions and sustainability were not researched.
How new research is added
New studies are found by a saved PubMed search and placed in a review queue before the page changes.
Lab markers
What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".
Metabolic 1
Triglycerides (a blood fat), from omega-3 supplement trials
Lowered in trials
A type of fat in the blood. High levels are linked to heart disease risk.
Not enough evidenceResults and what it means
Why it was measured
Omega-3 fats are known to act on triglycerides.
Statistical vs. clinical meaning
Established for omega-3 capsules, but not tested for eating oily fish in this review, so it is insufficient for the food.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 1 | Long-chain omega-3 lowered triglycerides by about 15% in a dose-dependent way (high-certainty evidence), mainly from supplement trials | Adults in randomised trials | Mostly omega-3 capsules |
Other 3
Omega-3 index (EPA and DHA in red blood cells)
Raised in trials
The share of the omega-3 fats EPA and DHA in the membranes of red blood cells. It is used as a blood marker of omega-3 intake.
Low certaintyResults and what it means
Why it was measured
To see whether eating fish actually changes the body's omega-3 level.
Statistical vs. clinical meaning
Eating fish raised a blood marker in a small trial. It is not a heart attack or death, so it does not prove a health benefit.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 4 | Omega-3 index rose by about 2.27 percentage points with two fish meals a week, and by about 2.03 with a 700 mg EPA+DHA capsule, versus control | 40 healthy adults aged 18 to 30 with low fish intake | Two fish meals a week (one oily, one white) for 8 weeks |
Blood fats and hs-CRP (an inflammation marker)
No significant change in trials
Cholesterol and other blood fats, and hs-CRP, a blood test that goes up with inflammation.
Low certaintyResults and what it means
Why it was measured
These are common heart-risk markers.
Statistical vs. clinical meaning
No clear change in these markers in a small, short trial of healthy young adults.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 4 | No significant effect on blood lipids or hs-CRP from two fish meals a week or from the capsule | 40 healthy young adults | Two fish meals a week for 8 weeks |
Attention and mental flexibility test scores (children)
Improved in trials
Scores from computer tasks that measure how well a child pays attention and switches between tasks.
Low certaintyResults and what it means
Why it was measured
These are used to see whether diet changes thinking in children.
Statistical vs. clinical meaning
Part scores improved; the overall score did not clearly. One trial.
Safety implication
None specific.
| Study | Result | People | Product |
|---|---|---|---|
| 7 | Fewer attention errors (-1.9, 95% CI -3.4 to -0.3) and faster reaction time in a complex versus simple task (-51 ms, -94 to -7) with oily fish than poultry; overall cognitive score +0.17 (-0.01 to 0.35) | 199 healthy children aged 8 to 9 | About 300 g a week of oily fish for 12 weeks |
Safety
What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.
Main points to know 3
- Fish is a major food allergen. The US FDA lists fish among the nine major food allergens, and MedlinePlus lists fish among the most common food allergies in older children and adults. Reactions range from hives and lip swelling to anaphylaxis. The NHS says people allergic to one type of fish often react to others, and that cooking does not make a reaction less likely. If you have a fish allergy, oily fish is not safe for you. Authoritative guidance 9 15 16
- Mercury and other pollutants, especially in pregnancy and childhood. People are mainly exposed to mercury (as methylmercury) by eating fish and shellfish, and large predatory fish are more likely to have high levels (WHO). Mercury is a particular threat to a baby in the womb and in early life. The NHS says oily fish usually have higher pollutant levels than other seafood, so it limits oily fish for girls, women who may become pregnant, and pregnant or breastfeeding women. The FDA and EPA sort fish into Best Choices, Good Choices and Choices to Avoid by mercury level. Authoritative guidance 18 16 10
- Pregnancy: raw and cold-smoked fish, and certain species. The NHS says to avoid raw fish, sushi made with raw fish (even if frozen), swordfish, shark and marlin in pregnancy. Cold-smoked and cured fish, such as smoked salmon, must be cooked until steaming hot because of listeria, which can cause miscarriage or stillbirth. Cooked fish and sushi made with cooked fish are listed as safe to eat. Authoritative guidance 17
Side effects 4
| Effect | How often | Severity and recovery | Evidence |
|---|---|---|---|
| Allergic reactions to fish, from hives and lip swelling to anaphylaxis No prevalence figure was read for this page. | Not established | can be severe (anaphylaxis) Not described in the sources read. | Authoritative guidance 9 15 |
| Higher mercury and pollutant intake if high-mercury species are eaten or if oily fish is eaten often during pregnancy or childhood The risk depends on the species. Salmon, sardines, herring, Atlantic and Pacific chub mackerel and freshwater trout are on the FDA/EPA Best Choices list; king mackerel is a Choice to Avoid. | Not established | can harm a developing baby's nervous system (WHO, NHS) Not described in the sources read. | Authoritative guidance 18 16 |
| Food poisoning from fish that is not fresh or not stored well; listeriosis from cold-smoked or cured fish in pregnancy Not described for oily fish specifically beyond the storage and cooking rules. | Not established | can be serious in pregnancy Not described in the sources read. | Authoritative guidance 16 17 |
| Possible higher heart risk with fried fish A 2021 review linked fried fish with higher risk of heart events. The NHS says frying can increase fat and calls steamed, baked or grilled fish a healthier choice. | Not established | Not stated Not stated | Observational 3 16 |
Liver
No liver injury from eating oily fish was found in the sources read. A liver-safety source such as LiverTox was not searched.
How often. No frequency was found.
Monitoring. No agency monitoring advice was found.
This is a safety connection. It is not evidence that Oily Fish supports liver health.
Medicines and supplements 1
| With | Why it matters | Importance | Evidence | What to do |
|---|---|---|---|---|
| Medicines in general prescription | Not described. | No interaction between eating oily fish and any medicine was described in the sources read (the NHS, FDA/EPA and WHO pages and the studies). Medicine interactions of omega-3 capsules were not searched and are a separate question. | Not found Not enough evidence 16 | Ask a pharmacist or doctor about a specific medicine, and especially about fish oil capsules, which are a different product. |
Who should check first 2
| Situation | Advice | Evidence |
|---|---|---|
| Known or suspected fish allergy | Avoid oily fish and read labels; in the US packaged foods must name the fish species. Ask an allergist. People allergic to one fish often react to others. | Authoritative guidance 9 16 |
| Pregnancy: raw fish, sushi with raw fish, swordfish, shark, marlin | The NHS says to avoid these in pregnancy. Ask your midwife or doctor. | Authoritative guidance 17 |
Overdose, product quality and regulators
Summary. The toxicity question for oily fish is mercury and other pollutants, not the fish itself. The sources read give species lists and portion limits for groups at higher risk, not a general limit for healthy adults.
Animal. Not reviewed.
High dose or long term signals. The NHS says pollutants in oily fish can build up in the body and may affect the future development of a baby. WHO says mercury is toxic to the nervous, digestive and immune systems, lungs, kidneys, skin and eyes.
Overdose response. Not found.
Genotoxicity. Not researched.
Mercury is the main contaminant the agencies name; other pollutants are mentioned by the NHS without being named. Levels differ by species, size and where the fish was caught.
Mercury by species (FDA and EPA chart, March 2024). Best Choices include anchovy, Atlantic mackerel, Pacific chub mackerel, herring, salmon, sardine, freshwater trout and canned light tuna. Good Choices include Spanish mackerel, albacore tuna and bluefish. Choices to Avoid include king mackerel, shark, swordfish, marlin and bigeye tuna. 10
Fish caught by family or friends. The FDA says to check local fish advisories. If there is none, eat only one serving and no other fish that week. 10
Storage and hygiene. The NHS says fish that is not fresh or not stored and prepared hygienically can cause food poisoning; keep it chilled or frozen, covered, and apart from cooked food. 16
| Body | Action | Date |
|---|---|---|
| US FDA and EPA (United States) | Advice about Eating Fish: for pregnancy and breastfeeding, 2 to 3 servings a week (4 ounces each) from Best Choices or 1 serving from Good Choices; for children, 2 servings a week from Best Choices with smaller serving sizes by age; check local advisories for fish caught by family or friends. Fish eaten as part of a healthy eating pattern may have heart health benefits (strong evidence per the page). source | 2024-03-05 |
| NHS (UK) (United Kingdom) | Fish and shellfish: oily fish listed (herring, pilchards, salmon, sardines, sprats, trout, mackerel; tuna does not count). Girls, women who may become pregnant, and pregnant or breastfeeding women should have no more than 2 portions (about 140 g each) of oily fish a week. Avoid shark, swordfish and marlin in pregnancy and for under-16s. source | 2026-06-26 |
| NHS (UK) (United Kingdom) | Foods to avoid in pregnancy: no raw fish or sushi with raw fish, no swordfish, shark or marlin; cold-smoked and cured fish must be cooked until steaming hot; oily fish no more than 2 portions a week. source | 2026-06-15 |
| US FDA (United States) | Food Allergies: fish is one of nine major food allergens; packaged food labels must name the fish species. source | 2026-03-11 |
| WHO (International) | Mercury and health: methylmercury exposure is mainly from fish and shellfish; large predatory fish are more likely to have high levels; mercury threatens the child in the womb and early in life. source | 2024-10-24 |
When to get medical help
- Trouble breathing, wheezing, swelling of the lips, face, tongue or throat, a hoarse voice, or widespread hives after eating fish: call 911 or your local emergency number. Do not wait to see if it passes.
- Vomiting, diarrhoea or fever after eating fish, especially in pregnancy or with a weak immune system: contact a doctor or midwife.
Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.
General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.
Frequently asked questions
What counts as oily fish?
The NHS lists herring (including kippers and bloaters), pilchards, salmon, sardines, sprats, trout and mackerel. It says fresh and canned tuna do not count. Canned sardines, pilchards and tinned salmon are fine, and their bones are edible.
Does eating oily fish protect the heart?
Do people who eat more fish live longer?
Slightly, in observational data. Across 12 cohorts the highest fish intake went with about 6% lower risk of death from any cause (RR 0.94). This cannot show that fish is the reason.
Is eating fish the same as taking fish oil capsules?
No. The 86-trial Cochrane review is mostly of capsules and found little or no effect on deaths or heart events; its authors say there is little evidence on eating fish. In one small trial both two fish meals a week and a capsule raised the blood omega-3 index. See the linked page on cod liver oil and fish oil.
Is fried fish as healthy as baked fish?
Is oily fish safe in pregnancy?
Yes within limits, per the agencies. The NHS says no more than 2 portions of oily fish a week and to avoid raw fish, swordfish, shark and marlin, and to cook smoked salmon until steaming hot. The FDA and EPA suggest 2 to 3 servings a week from their Best Choices list. Ask your midwife or doctor.
Should I worry about mercury in oily fish?
Does canned oily fish count?
Can oily fish cause an allergic reaction?
Does eating fish help the brain or protect against dementia?
Observational studies link higher fish intake with lower risk of cognitive impairment and dementia (RR about 0.82 in a 2024 pooled analysis of 35 studies), but the authors want more studies for dementia. One 12-week trial in 199 children had mixed results, with the overall thinking score not clearly better.
Does eating fish affect type 2 diabetes?
No benefit was seen. A pooled analysis of 28 cohorts found no link in men and a slightly higher risk in women (IRR 1.04 per extra 100 g a week of fatty fish). It does not prove fish causes diabetes.
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Editorial transparency
- Written by
- AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
- Medical review
- None. This page has not been reviewed by a physician or pharmacist.
- First published
- 2026-10-26
- Last substantive update
- 2026-10-26
- How we research
- We started from our earlier oily fish page, then re-read the NHS, FDA, EPA, MedlinePlus and WHO pages and the PubMed abstracts for every study cited, and added studies on dementia, children and type 2 diabetes. Only abstracts were read for studies. Items we could not verify are flagged in the research gaps.
- How we rate evidence
- See "How we rate evidence" in the Evidence tab.
- Independence
- No product is promoted on this page. No affiliate links are shown. Funding is not stated in most abstracts; the type 2 diabetes analysis lists UK public research funders.
Sources 18
Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.
- Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, et al.. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease.. Cochrane Database Syst Rev. 2020. PMID 32114706. DOI 10.1002/14651858.CD003177.pub5. (abstract)
- Godos J, Micek A, Currenti W, Franchi C, Poli A. Fish consumption, cognitive impairment and dementia: an updated dose-response meta-analysis of observational studies.. Aging Clin Exp Res. 2024. PMID 39162889. DOI 10.1007/s40520-024-02823-6. (abstract)
- Krittanawong C, Isath A, Hahn J, Wang Z, Narasimhan B, et al.. Fish Consumption and Cardiovascular Health: A Systematic Review.. Am J Med. 2021. PMID 33444594. DOI 10.1016/j.amjmed.2020.12.017. (abstract)
- McMullan JE, Kumar RA, Yeates AJ, Allsopp PJ, Mulhern MS, et al.. Influence of Fish Consumption and omega-3 Supplementation on the omega-3 Index of Young Adults: A 2 x 2 Factorial Randomized Controlled Trial (YouFish Study).. J Nutr. 2025. PMID 41082976. DOI 10.1016/j.tjnut.2025.10.010. (abstract)
- Pastorino S, Bishop T, Sharp SJ, Pearce M, Akbaraly T, et al.. Heterogeneity of Associations between Total and Types of Fish Intake and the Incidence of Type 2 Diabetes: Federated Meta-Analysis of 28 Prospective Studies Including 956,122 Participants.. Nutrients. 2021. PMID 33917229. DOI 10.3390/nu13041223. (abstract)
- Starling P, Charlton K, McMahon AT, Lucas C. Fish intake during pregnancy and foetal neurodevelopment--a systematic review of the evidence.. Nutrients. 2015. PMID 25793632. DOI 10.3390/nu7032001. (abstract)
- Teisen MN, Vuholm S, Niclasen J, Aristizabal-Henao JJ, Stark KD, et al.. Effects of oily fish intake on cognitive and socioemotional function in healthy 8-9-year-old children: the FiSK Junior randomized trial.. Am J Clin Nutr. 2020. PMID 32529206. DOI 10.1093/ajcn/nqaa050. (abstract)
- Zhao LG, Sun JW, Yang Y, Ma X, Wang YY, et al.. Fish consumption and all-cause mortality: a meta-analysis of cohort studies.. Eur J Clin Nutr. 2016. PMID 25969396. DOI 10.1038/ejcn.2015.72. (abstract)
- . US FDA: Food Allergies. . . (full-text)
- . FDA and EPA: Advice about Eating Fish. . . (full-text)
- . GBIF Backbone: Clupea harengus (Atlantic herring). . . (full-text)
- . GBIF Backbone: Salmo salar (Atlantic salmon). . . (full-text)
- . GBIF Backbone: Sardina pilchardus (European pilchard or sardine). . . (full-text)
- . GBIF Backbone: Scomber scombrus (Atlantic mackerel). . . (full-text)
- . MedlinePlus: Food allergy. . . (full-text)
- . NHS: Fish and shellfish. . . (full-text)
- . NHS: Foods to avoid in pregnancy. . . (full-text)
- . WHO: Mercury and health. . . (full-text)
