Fish represents one of the most nutritionally valuable foods available, offering high-quality protein, essential omega-3 fatty acids, and important micronutrients including vitamin D, vitamin B12, iodine, and selenium. Choosing healthy fish to eat involves balancing nutritional benefits—particularly omega-3 content—with safety considerations such as mercury levels and sustainability. The NHS recommends consuming at least two portions of fish weekly, with one portion being oily fish, to support cardiovascular health, neurological function, and overall wellbeing. This guidance applies to most adults, though pregnant women, children, and individuals with specific health conditions require tailored advice to optimise benefits whilst minimising potential risks.

What Makes Fish a Healthy Food Choice?

Fish represents one of the most nutritionally valuable protein sources available, offering a combination of high-quality protein, essential fatty acids, and important micronutrients. Unlike many terrestrial protein sources, fish is naturally low in saturated fat whilst being rich in polyunsaturated fats, particularly the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These long-chain fatty acids play important roles in cardiovascular health, neurological function, and inflammatory regulation.

The nutritional profile of fish extends beyond omega-3 content. Oily fish varieties are a leading dietary source of vitamin D, which is particularly important in the UK where sunlight exposure is limited during winter months (white fish contains much less vitamin D). Fish also contains significant amounts of vitamin B12, iodine, and selenium—micronutrients essential for thyroid function, red blood cell formation, and antioxidant defence mechanisms. White fish varieties offer lean protein with minimal fat content, whilst oily fish provides the added benefit of fat-soluble vitamins.

The NHS recommends fish as part of a balanced diet, with specific guidance to include at least two portions weekly. The protein in fish contains all essential amino acids, making it a complete protein source that supports muscle maintenance, immune function, and cellular repair. Furthermore, fish protein is highly digestible compared to some meat sources, making it suitable for individuals with sensitive digestive systems.

From a cardiovascular perspective, regular consumption of oily fish has been associated with reduced risk of coronary heart disease. The evidence for stroke and cardiac arrhythmias is less consistent. The anti-inflammatory properties of omega-3 fatty acids may also benefit individuals with chronic inflammatory conditions, though patients should discuss significant dietary changes with their GP. Normal dietary fish consumption is safe for people taking anticoagulant medications, though high-dose omega-3 supplements should be discussed with healthcare professionals.

Healthiest Fish Options in the UK

When selecting fish for optimal health benefits, both nutritional content and sustainability considerations should guide choices. Oily fish represent the most nutrient-dense options and include:

• Salmon (wild or farmed): Rich in omega-3s, vitamin D, and B vitamins. Omega-3 content can vary between wild and farmed salmon depending on feed, season and cut, though both remain nutritionally valuable and farmed salmon is often more affordable.

• Mackerel: One of the highest omega-3 sources available, also providing substantial vitamin B12 and selenium. Fresh mackerel is preferable to smoked varieties which are typically higher in salt.

• Sardines and pilchards: High in omega-3s and calcium (when bones are consumed). These small fish accumulate fewer environmental contaminants due to their position in the food chain.

• Herring: Excellent omega-3 content with good vitamin D levels. Available fresh, pickled, or smoked, though smoked and pickled versions are typically higher in salt.

• Trout (particularly rainbow trout): Widely available in the UK, offering good omega-3 content. Check for sustainability certifications as environmental impact varies by production method.

White fish varieties provide lean protein with minimal fat and include cod, haddock, plaice, and pollock. Whilst lower in omega-3s than oily fish, they offer excellent protein quality and are suitable for individuals requiring lower-fat options. Shellfish such as mussels, oysters, and prawns provide high-quality protein, zinc, and selenium, though they contain less omega-3 than oily fish.

The Marine Conservation Society's Good Fish Guide provides updated sustainability ratings for UK-available fish. Choosing sustainably sourced options ensures long-term availability whilst supporting responsible fishing practices. Look for Marine Stewardship Council (MSC) certification or consult your fishmonger regarding sourcing practices. Frozen fish retains nutritional value comparable to fresh fish and often represents better value whilst reducing food waste.

It's important to note that canned tuna is not considered an oily fish in UK dietary guidance, despite being derived from an oily fish species, as the canning process reduces the omega-3 content.

Omega-3 Benefits and Which Fish Contain Them

Omega-3 fatty acids, particularly EPA and DHA, exert wide-ranging physiological effects throughout the body. These essential fatty acids cannot be synthesised efficiently by humans and must be obtained through diet. The cardiovascular benefits are well-established: omega-3s can reduce triglyceride levels, lower blood pressure modestly, and may decrease platelet aggregation. NICE guidance (NG238) does not recommend omega-3 supplements for primary prevention of cardiovascular disease in the general population, though dietary sources remain important for overall health. For specific high-risk individuals with elevated triglycerides and cardiovascular disease, prescription icosapent ethyl (a purified EPA) may be considered (NICE TA805).

Neurologically, DHA comprises a significant structural component of brain cell membranes and is important for cognitive function throughout life. Adequate omega-3 intake during pregnancy supports foetal brain development, whilst maintaining intake in later life may help preserve cognitive function, though evidence for preventing dementia remains inconclusive. The anti-inflammatory properties of omega-3s may provide modest benefits for individuals with rheumatoid arthritis and other chronic inflammatory conditions, though these effects are adjunctive rather than curative.

Approximate omega-3 (EPA+DHA) content varies between fish species:

• Higher sources (>1g per 100g): Mackerel, herring, sardines, fresh tuna, salmon

• Moderate sources (0.5-1g per 100g): Trout, anchovies, sea bass

• Lower sources (<0.5g per 100g): Cod, haddock, plaice, canned tuna, prawns

The NHS recommends consuming at least one portion of oily fish weekly to achieve beneficial omega-3 levels. One portion equals approximately 140g cooked weight. Cooking methods affect omega-3 retention: grilling, baking, and steaming preserve omega-3 content better than deep frying.

Normal dietary fish consumption is safe for individuals taking anticoagulant medications. High-dose omega-3 supplements may have mild anticoagulant effects, particularly with warfarin, so discuss these with your GP or anticoagulation clinic before starting them. Direct oral anticoagulants (DOACs) generally have fewer dietary interactions than warfarin.

Mercury Levels and Fish Safety Considerations

Mercury contamination represents the primary safety concern regarding fish consumption, particularly for vulnerable populations. Mercury exists in aquatic environments as methylmercury, which bioaccumulates in fish tissue and biomagnifies up the food chain. Large, long-lived predatory fish accumulate the highest mercury concentrations. Methylmercury crosses the placental barrier and can affect foetal neurological development, making dietary precautions essential during pregnancy and for young children.

The UK Food Standards Agency (FSA) and NHS provide specific guidance for vulnerable groups:

Pregnant women, women planning pregnancy, and children under 16 should:

• Avoid: Shark, swordfish, and marlin entirely due to high mercury levels

• Limit: Tuna to no more than two fresh tuna steaks (140g cooked weight) or four medium cans weekly

• Limit oily fish: Maximum two portions weekly (due to potential pollutant accumulation)

General population should:

• Limit shark, marlin and swordfish to no more than one portion per week

• Limit oily fish to four portions weekly for men and boys, and two portions weekly for women and girls (who may become pregnant). This precaution addresses potential accumulation of dioxins and polychlorinated biphenyls (PCBs) alongside mercury concerns.

Lower-mercury fish options suitable for frequent consumption include salmon, sardines, Atlantic mackerel (commonly sold in the UK), trout, and most white fish (cod, haddock, plaice). These species accumulate minimal mercury due to their size, lifespan, and position in the food chain.

Shellfish safety requires additional consideration. Raw or undercooked shellfish may harbour pathogenic bacteria or viruses (particularly norovirus). Pregnant women, immunocompromised individuals, and those with liver disease should consume only thoroughly cooked shellfish. Individuals with shellfish allergies must avoid these entirely, as allergic reactions can be severe and potentially life-threatening.

If you experience symptoms of severe allergic reaction following fish consumption—such as swelling of the throat/tongue, difficulty breathing, or dizziness/collapse—call 999 immediately. For other symptoms such as gastrointestinal upset or mild allergic reactions, contact your GP promptly. Scombroid poisoning (from improperly stored oily fish) and ciguatera poisoning (rare in UK-sourced fish) require medical assessment.

How Often Should You Eat Fish for Optimal Health?

The NHS recommends consuming at least two portions of fish weekly, with one portion being oily fish. This recommendation balances optimal nutrient intake against potential contaminant exposure. One portion equals approximately 140g cooked weight. This guidance aligns with evidence from large epidemiological studies demonstrating cardiovascular benefits at this consumption frequency.

For cardiovascular health, consuming oily fish 1-2 times weekly appears sufficient to reduce coronary heart disease risk. NICE guidance (NG238) on cardiovascular disease prevention acknowledges dietary omega-3 from fish as beneficial, though it does not recommend omega-3 supplements for primary prevention in the general population. For certain high-risk individuals with established cardiovascular disease and elevated triglycerides, prescription icosapent ethyl (NICE TA805) may be considered. Individuals with established cardiovascular disease should discuss optimal fish intake with their GP or cardiologist.

Practical implementation strategies include:

• Vary your choices: Rotate between different fish species to maximise nutrient diversity whilst minimising exposure to any single contaminant source

• Include both oily and white fish: Oily fish for omega-3 benefits; white fish for lean protein

• Consider canned options: Canned sardines, mackerel, and salmon offer convenience, affordability, and comparable nutrition to fresh fish (note that canned tuna does not count as an oily fish)

• Preparation methods: Grilling, baking, poaching, or steaming preserves nutritional value better than deep frying

Special populations require tailored advice:

• Pregnant and breastfeeding women: Two portions weekly (one oily), avoiding high-mercury species

• Children: Introduce fish from weaning onwards; boys can consume up to four oily fish portions weekly, girls should limit to two

• Individuals with fish allergies: Seek dietitian guidance for alternative omega-3 sources (walnuts, flaxseeds, chia seeds provide ALA, though conversion to EPA/DHA is limited)

• Vegetarians/vegans: Algae-based omega-3 supplements provide EPA and DHA without fish consumption

If you have specific health conditions, take multiple medications, or have concerns about fish consumption, consult your GP or request referral to a registered dietitian for personalised advice. Individuals with gout should note that some fish (particularly sardines, anchovies, and mackerel) are high in purines, though moderate consumption is generally acceptable within an overall balanced diet.

Frequently Asked Questions