Omega-3 Fatty Acids in Foods: Fish, Walnuts, Flax and Chia
Where omega-3 fatty acids occur in foods (fish, walnuts, flax, chia), how plant ALA differs from fish EPA and DHA, and what fish-eating studies found, kept apart from supplements.
Content last updated . This page has not been medically reviewed.
Safety first. Supplements can cause side effects and interact with medicines. Read mushroom safety and interactions before you use any mushroom product.
Short answer: Omega-3s in food come in two families. EPA and DHA are found in seafood, especially cold-water fish. ALA is found in plant foods such as flaxseed, chia seeds and walnuts. [1] Studies of eating fish are mostly observational, and fish-oil capsules are a separate topic.
The two families
| Type | Where it is found | Notes from the sources |
|---|---|---|
| EPA and DHA | Seafood, especially cold-water fish such as salmon, mackerel and tuna, and shellfish; also fish oil supplements. [1] | NHS: oily fish is the richest source of long-chain omega-3; some white fish and shellfish contain it but not as much. [2] |
| ALA (alpha-linolenic acid) | Plant oils such as flaxseed, soybean and canola, and plant foods such as chia seeds and walnuts. [1] | Reviews say the body converts ALA to EPA and DHA with very limited efficiency, particularly for DHA. [3] |
Plant names: flax is Linum usitatissimum, chia is Salvia hispanica and walnut is Juglans regia. [4] Specific pages: flaxseed, chia seeds, walnuts and oily fish.
What research shows
| Question | What the source found | Strength of evidence |
|---|---|---|
| Fish eating and heart disease | A systematic review of 24 observational studies (714,526 people) found non-fried fish was probably linked to fewer cardiovascular events, and fried fish to more. It found no association with stroke. [5] | Observational only |
| Seafood versus supplements | NCCIH notes that for some conditions the evidence for seafood is stronger than for supplements, that other nutrients in seafood may play a role, and that seafood eaters tend to have healthier lifestyles. [1] | Context, not a trial |
| Plant omega-3 and EPA and DHA levels | A scoping review of 13 trials found high-dose flaxseed or echium seed oil supplements gave no increase in the omega-3 index, while microalgal oil did. [6] | Limited (oil supplements, not whole seeds) |
| Whole plant foods (walnuts, flax, chia) | Proper evidence not found here. We searched PubMed for ALA conversion; the reviews read concern oils and general conversion, not whole foods. | Insufficient evidence in the sources read |
Official guidance, as read
- The US Dietary Guidelines for Americans 2020 to 2025 recommend that adults eat 8 ounces or more of a variety of seafood a week, with smaller amounts for young children. [1]
- The UK NHS advises at least one portion (about 140 g cooked) of oily fish a week. It advises girls, women who may become pregnant and pregnant or breastfeeding women to have no more than two portions a week, because pollutants in oily fish may build up in the body. [2]
Supplements are a different topic
Fish oil, krill oil and algal oil are covered under omega-3 evidence by use. Results from capsule trials should not be read as results for eating fish.
Frequently asked questions
Does eating fish protect the heart?
A review of observational studies found non-fried fish probably linked to fewer cardiovascular events. [5] That shows an association, not proof.
Are flax and chia as good as fish for omega-3?
They contain a different type, ALA, and its conversion to EPA and DHA is very limited. [3] We did not find a direct trial of whole flax or chia versus fish.
How much fish do official bodies suggest?
US guidelines: 8 ounces or more of a variety of seafood per week for adults. [1] NHS: at least one portion of oily fish a week, and no more than two for pregnant or breastfeeding women. [2]
Can I get EPA and DHA without fish?
The review we read found that microalgal oil supplements raised the omega-3 index while flaxseed oil did not. [6] Ask a clinician or dietitian about your situation.
Should I take a supplement instead?
Seafood and supplements are not interchangeable in the evidence; NCCIH says the seafood evidence is stronger for some conditions. [1]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and individual considerations
- Fish and shellfish allergy is a reason to avoid those foods. For emergency signs after eating, see food allergy basics. Call 911 for trouble breathing or swelling of the face or throat.
- Pregnancy and mercury: see fish and mercury and pregnancy and breastfeeding.
- Fried fish was linked to more cardiovascular events in the review above. [5]
- Medicines: the food sources we read did not describe interactions for fish or ALA foods. Capsules are different; read omega-3 safety and interactions and ask a pharmacist.
References
- Omega-3 Supplements: What You Need To Know. National Center for Complementary and Integrative Health (US). Read 2026-10-23.
- Fish and shellfish in your diet. NHS (UK). Read 2026-10-23.
- Current Insights into the Effects of Dietary α-Linolenic Acid Focusing on Alterations of Polyunsaturated Fatty Acid Profiles in Metabolic Syndrome. Int J Mol Sci 2024. PMID 38732139. Read 2026-10-23.
- GBIF Backbone Taxonomy species match. Global Biodiversity Information Facility. Accepted names checked 2026-10-23.
- Fish Consumption and Cardiovascular Health: A Systematic Review. Am J Med 2021. PMID 33444594. Read 2026-10-23.
- Bioavailability and conversion of plant based sources of omega-3 fatty acids: a scoping review to update supplementation options for vegetarians and vegans. Crit Rev Food Sci Nutr 2022. PMID 33576691. Read 2026-10-23.