Omega-3 fatty acids are essential polyunsaturated fats that support cardiovascular health, brain function, and inflammatory regulation. Fish high in omega-3 fats, particularly oily species such as mackerel, salmon, and sardines, provide the most bioavailable forms—eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The NHS recommends at least one portion of oily fish weekly to help meet the UK population target of 450 mg combined EPA and DHA daily. However, National Diet and Nutrition Survey data reveal that many UK adults consume less than half this amount. Understanding which fish are richest in omega-3 and how to incorporate them safely into your diet can support long-term health whilst minimising exposure to environmental contaminants.

What Are Omega-3 Fats and Why Are They Important?

Omega-3 fatty acids are a family of essential polyunsaturated fats that the human body cannot synthesise in sufficient quantities, making dietary intake crucial for health. The three main types are alpha-linolenic acid (ALA), found primarily in plant sources, and the longer-chain eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are predominantly obtained from marine sources, particularly oily fish.

These fatty acids play vital structural and functional roles throughout the body. DHA is a major structural component of cell membranes, particularly in the brain and retina, where it supports cognitive function and visual development. EPA and DHA serve as precursors to bioactive lipid mediators called resolvins and protectins, which help regulate inflammatory responses and may support cardiovascular health. Research suggests that adequate omega-3 intake is associated with reduced triglyceride levels, improved endothelial function, and potentially lower risk of coronary heart disease.

The UK Scientific Advisory Committee on Nutrition (SACN) and Committee on Toxicity (COT) advise a population recommendation of 450 mg of combined EPA and DHA daily for adults. However, National Diet and Nutrition Survey (NDNS) data consistently show that average UK intakes fall below this target, with many adults consuming less than half the recommended amount. This shortfall has prompted public health guidance emphasising the importance of regular oily fish consumption.

Unlike some nutrients that can be stored in the body for extended periods, omega-3 fatty acids require consistent dietary intake to maintain optimal tissue levels. The body can convert some plant-based ALA to EPA and DHA, but this conversion is generally inefficient (typically less than 10%, with variations between individuals), making direct consumption of marine omega-3s particularly valuable for meeting physiological requirements.

Which Fish Are Highest in Omega-3 Fatty Acids?

Oily fish species contain substantially higher concentrations of omega-3 fatty acids compared to white fish, with levels varying considerably depending on the species, diet, and habitat. The following fish are recognised as excellent sources of EPA and DHA:

Highest omega-3 content (approximate ranges per 100g cooked portion):

• Mackerel – typically provides 1.5–3.0g of omega-3, making it one of the richest readily available sources

• Salmon – contains approximately 1.5–2.5g, with levels varying by species, season and diet

• Herring – delivers around 1.5–2.0g and is widely available fresh, smoked, or pickled

• Sardines – offer approximately 1.0–2.0g and are convenient tinned options

• Trout (rainbow) – provides roughly 0.5–1.5g, with variation based on diet

Moderate omega-3 sources:

• Anchovies – contain about 1.0–1.5g and are often used in Mediterranean cuisine

• Pilchards – similar to sardines, providing around 1.0–1.5g

• Fresh tuna – offers approximately 0.5–1.5g, though tinned tuna contains significantly less due to processing

It is important to note that white fish such as cod, haddock, and plaice contain minimal omega-3 (typically less than 0.3g per 100g) as these species store fat in their liver rather than muscle tissue. The NHS specifically advises that tinned tuna, despite coming from an oily fish species, does not count towards the recommended weekly intake of oily fish due to its lower omega-3 content after processing.

The omega-3 content can vary depending on whether fish are wild-caught or farmed, their diet, and seasonal factors. Both farmed and wild fish can be good sources of omega-3, with levels primarily influenced by the fish's diet rather than farming method alone.

Health Benefits of Eating Omega-3 Rich Fish

Regular consumption of fish high in omega-3 fatty acids is associated with multiple evidence-based health benefits, supported by extensive epidemiological and clinical research. The cardiovascular benefits are particularly well-established, with NICE acknowledging omega-3s as part of heart-healthy dietary patterns.

Cardiovascular health: High-dose prescription omega-3 fatty acids (2-4g daily) have been shown to reduce serum triglyceride concentrations by 20–30% in individuals with hypertriglyceridaemia. Dietary omega-3s from fish may support healthy blood pressure and reduce platelet aggregation. Observational studies suggest that consuming oily fish at least twice weekly is associated with a reduced risk of fatal coronary heart disease. However, it's important to note that NICE guidance (NG238) does not recommend omega-3 supplements for the prevention of cardiovascular disease. The potential mechanisms include improved endothelial function, reduced inflammation, and favourable effects on heart rate variability.

Brain and cognitive function: DHA comprises approximately 40% of polyunsaturated fatty acids in the brain and is essential for neuronal membrane integrity and neurotransmitter function. The European Food Safety Authority (EFSA) recognises that maternal DHA intake contributes to normal brain and eye development in the foetus and breastfed infants. In adults, higher omega-3 status has been associated with better cognitive performance, though evidence for preventing cognitive decline or dementia remains inconclusive.

Anti-inflammatory effects: Omega-3 fatty acids compete with omega-6 fatty acids in inflammatory pathways, leading to production of less inflammatory eicosanoids. This may benefit individuals with inflammatory conditions, though fish consumption should complement rather than replace conventional medical treatment.

Mental health: Some observational studies suggest associations between higher fish consumption and reduced risk of depression, though clinical trial evidence for omega-3 supplementation in treating depression shows mixed results. There is no official link established that would support omega-3 as a standalone treatment for mental health conditions.

Other potential benefits include support for healthy pregnancy outcomes, joint health in inflammatory arthritis, and maintenance of healthy vision, though individuals should discuss specific health concerns with their GP rather than relying solely on dietary changes.

How Much Omega-3 Fish Should You Eat Weekly?

The NHS recommends that adults eat at least two portions of fish per week, with one portion being oily fish. A standard portion is defined as approximately 140g cooked weight (or about 170g raw weight), which equates to a piece roughly the size of an adult's hand.

For most adults, one 140g portion of oily fish weekly provides approximately 1.0–3.5g of combined EPA and DHA (depending on the species), which can help meet the UK population recommendation of 450mg daily when averaged across the week. Those who wish to optimise their omega-3 intake may choose to consume oily fish twice weekly, though this should be balanced against safety considerations regarding environmental contaminants (discussed in the next section).

Practical portion examples:

• One small mackerel fillet (approximately 140g cooked)

• One medium salmon steak

• Two to three sardines

• One small trout

• One small tin of pilchards or sardines (approximately 120g drained weight)

Special population considerations:

Children can benefit from oily fish from age one onwards, with portion sizes adjusted according to age and appetite. According to Food Standards Agency guidance, boys can safely eat up to four portions of oily fish weekly, while girls should have no more than two portions weekly due to potential contaminant concerns.

For individuals who do not consume fish due to dietary preferences, allergies, or ethical reasons, alternative sources of omega-3 include microalgae-based supplements (which provide EPA and DHA directly), walnuts, flaxseeds, chia seeds, and rapeseed oil (which provide ALA). However, as noted earlier, conversion of ALA to EPA and DHA is limited, so those avoiding fish entirely should consider discussing supplementation with their GP or a registered dietitian.

It is worth noting that consuming more than the recommended amount does not necessarily confer additional benefits, and very high intakes may carry risks. The European Food Safety Authority (EFSA) considers combined EPA and DHA intakes up to 5g daily from all sources to be safe for adults, but such high doses should only be taken under medical supervision.

Safety Considerations and NHS Guidance on Fish Consumption

Whilst oily fish provides substantial health benefits, certain safety considerations must be observed due to potential accumulation of environmental contaminants, particularly mercury, dioxins, and polychlorinated biphenyls (PCBs). These persistent organic pollutants accumulate in the food chain, with higher concentrations found in larger, longer-lived predatory fish.

Mercury concerns: Methylmercury can affect the developing nervous system, making certain fish unsuitable for vulnerable groups. The NHS advises that:

• Pregnant women, women trying to conceive, and women who are breastfeeding should:
• Avoid shark, swordfish, and marlin entirely due to high mercury levels
• Limit tuna intake to no more than two fresh tuna steaks (about 140g cooked) or four medium-sized tins weekly

• Limit oily fish consumption to no more than two portions weekly

• Pregnant women should also avoid raw shellfish and fish liver oil supplements (due to high vitamin A content)

Dioxins and PCBs: These industrial contaminants accumulate in fatty tissues. Whilst levels in UK fish are generally within safe limits set by the European Commission, the Food Standards Agency (FSA) recommends that:

• Girls and women of childbearing age should consume no more than two portions of oily fish weekly

• Boys can eat up to four portions of oily fish weekly

• Men and women past childbearing age can safely eat up to four portions weekly if they wish

Practical safety measures:

• Choose a variety of fish species rather than relying on a single type

• Smaller fish (sardines, mackerel, herring) generally contain lower contaminant levels than larger predatory species

• Both farmed and wild fish are monitored for contaminants and are safe when consumed according to guidance

• Pregnant women should ensure fish is thoroughly cooked to reduce foodborne illness risk

When to seek medical advice: Individuals with fish allergies should avoid all fish products and carry prescribed adrenaline auto-injectors if anaphylaxis risk exists. Those taking anticoagulant medications (such as warfarin) should discuss with their healthcare provider before starting high-dose omega-3 supplements, as omega-3s may have mild antiplatelet effects. Anyone considering high-dose omega-3 supplements should discuss this with their GP, particularly if they have bleeding disorders or are scheduled for surgery.

If you experience any suspected adverse reactions to omega-3 supplements, report them through the MHRA Yellow Card Scheme.

The benefits of consuming oily fish according to NHS guidance substantially outweigh the risks for most people, and the recommendations are designed to maximise nutritional benefits whilst minimising exposure to environmental contaminants.

Frequently Asked Questions