Fatty fish, also known as oily fish, are species rich in omega-3 fatty acids distributed throughout their body tissues. Unlike lean white fish, which store fat primarily in the liver, fatty fish such as salmon, mackerel, and sardines contain significantly higher levels of essential omega-3s—particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These fish provide 5–20% fat by weight and are excellent sources of protein, vitamin D, vitamin B12, selenium, and iodine. The NHS recognises fatty fish as vital for cardiovascular health, neurological development, and overall wellbeing, recommending at least one portion weekly as part of a balanced diet.

What Are Fatty Fish?

Fatty fish, also known as oily fish, are species that contain significantly higher levels of omega-3 fatty acids in their tissues compared to white fish. Unlike lean fish such as cod or haddock, which store most of their fat in the liver, fatty fish distribute oils throughout their body tissues, giving them a richer flavour and darker flesh.

The defining characteristic of fatty fish is their omega-3 polyunsaturated fatty acid content, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These essential fatty acids can only be synthesised inefficiently by the human body from plant sources, making dietary intake the main source. A portion of fatty fish typically contains between 1.5 to 3 grams of long-chain omega-3 fatty acids (EPA+DHA), though this varies by species and preparation method.

From a nutritional perspective, fatty fish are also excellent sources of high-quality protein, vitamin D, vitamin B12, selenium, and iodine. The fat content in these fish ranges from approximately 5% to 20% by weight, which is considerably higher than the 2% or less found in white fish. This higher fat content contributes to their distinctive taste and texture, making them popular choices in both traditional British cuisine and contemporary healthy eating patterns.

The NHS recognises fatty fish as an important component of a balanced diet, particularly for cardiovascular health and neurological development. Understanding which fish qualify as 'fatty' helps individuals make informed dietary choices aligned with public health recommendations for omega-3 intake.

Types of Fatty Fish Commonly Available in the UK

The UK market offers a diverse range of fatty fish, both from domestic waters and imported sources. Salmon remains the most popular choice, with farmed Atlantic salmon widely available in supermarkets and fishmongers. Wild Pacific salmon is available seasonally or imported, while wild Atlantic salmon is relatively rare in UK retail.

Mackerel is another abundant fatty fish in British waters, particularly during summer and autumn months. This affordable option contains some of the highest levels of omega-3 fatty acids among commonly consumed fish. Fresh mackerel has a distinctive flavour and is often available smoked or preserved. Herring, including kippers (smoked herring), represents a traditional British fatty fish with excellent nutritional value. Rollmop herrings and Bismarck herrings are also popular preserved varieties.

Sardines and pilchards (which are actually the same species at different life stages) are typically available tinned in the UK, though fresh sardines can be found at fishmongers and some supermarkets. These small fish are generally considered sustainable options when sourced from well-managed fisheries. Trout, especially rainbow trout farmed in the UK, provides a milder-tasting alternative to salmon whilst still offering substantial omega-3 content.

Other fatty fish available include:

• Anchovies – usually preserved in oil or salt

• Fresh tuna – though according to NHS guidance, tinned tuna does not count as an oily fish portion as the canning process reduces the omega-3 content

• Swordfish – available fresh or frozen, though consumption should be limited due to mercury content

When selecting fatty fish, look for Marine Stewardship Council (MSC) certification or other sustainability labels to help identify responsibly sourced options. Fresh fish should have bright eyes, firm flesh, and a clean sea smell rather than a strong fishy odour.

Health Benefits of Eating Fatty Fish

Regular consumption of fatty fish is associated with several evidence-based health benefits, primarily attributed to their omega-3 fatty acid content. Cardiovascular health represents one of the most well-established areas. EPA and DHA are associated with reduced triglyceride levels, modest blood pressure reduction, and may be linked to lower risk of fatal coronary heart disease. While NICE acknowledges the potential benefits of dietary omega-3 fatty acids, it does not routinely recommend omega-3 supplements for cardiovascular disease prevention.

The anti-inflammatory properties of omega-3 fatty acids may benefit individuals with inflammatory conditions. These fatty acids are incorporated into cell membranes and influence the production of inflammatory mediators, potentially reducing chronic low-grade inflammation associated with various diseases. Some studies suggest potential benefits for rheumatoid arthritis symptoms when omega-3 intake is adequate, though this should be considered complementary to medical treatment.

Brain health and cognitive function are supported by DHA, which is a major structural component of brain tissue. Adequate omega-3 intake during pregnancy and early childhood is important for foetal and infant neurological development. The NHS recommends pregnant women consume fatty fish whilst observing safety limits. In older adults, regular fatty fish consumption may be associated with reduced cognitive decline, though there is no definitive evidence establishing prevention of dementia.

Mental health research suggests potential benefits, with some evidence indicating that populations consuming more fatty fish have lower rates of depression. However, the relationship is complex and likely influenced by multiple dietary and lifestyle factors. Fatty fish also provide vitamin D, essential for bone health, immune function, and mood regulation—particularly important in the UK where sunlight exposure is limited during winter months.

Additionally, the high-quality protein in fatty fish supports muscle maintenance, whilst selenium acts as an antioxidant. The combination of nutrients in fatty fish makes them a valuable component of dietary patterns associated with healthy ageing and chronic disease prevention.

How Much Fatty Fish Should You Eat?

The NHS recommends that adults consume at least two portions of fish per week, with one portion being an oily or fatty fish. A standard portion is defined as approximately 140 grams (cooked weight), which provides sufficient omega-3 fatty acids to confer health benefits. This recommendation aligns with guidance from the Scientific Advisory Committee on Nutrition (SACN) and supports cardiovascular health without excessive exposure to environmental contaminants.

For pregnant women, those planning pregnancy, and breastfeeding mothers, the guidance is more specific due to concerns about pollutants. These groups should limit fatty fish consumption to no more than two portions per week and avoid certain species entirely. Shark, swordfish, and marlin should be avoided due to high mercury levels, which can affect foetal neurological development. Tuna intake should be limited to no more than two tuna steaks (about 140g cooked weight each) or four medium-sized cans (about 140g drained weight each) per week. Pregnant women can safely consume salmon, trout, mackerel, herring, sardines, and pilchards within the two-portion limit.

Children's recommendations vary by age. Girls and women who might become pregnant in the future should consume no more than two portions of fatty fish weekly from an early age. Boys and men can safely eat up to four portions weekly. Children under 16 should avoid shark, swordfish, and marlin entirely. Introducing fatty fish during weaning (around 6 months) can be beneficial, ensuring bones are removed and fish is appropriately prepared.

For individuals with specific health conditions, recommendations may differ. Those with cardiovascular disease may benefit from regular fatty fish consumption as part of a Mediterranean-style diet, though specific advice should come from healthcare professionals. People taking anticoagulant medications should maintain consistent omega-3 intake rather than making sudden large changes, as very high doses of omega-3 (typically from supplements rather than dietary sources) may have mild antiplatelet effects.

It is worth noting that more is not necessarily better. Exceeding recommended amounts increases exposure to environmental contaminants such as dioxins and polychlorinated biphenyls (PCBs) without proportional health benefits. If you dislike fish or follow a plant-based diet, alternative omega-3 sources include flaxseed, chia seeds, walnuts and rapeseed oil (containing alpha-linolenic acid, ALA), or algae-based supplements (containing EPA and DHA). Speak with your GP or a registered dietitian about appropriate options.

Choosing and Preparing Fatty Fish Safely

Selecting high-quality fatty fish ensures both optimal nutrition and food safety. When purchasing fresh fish, look for clear, bright eyes, shiny skin with intact scales, firm flesh that springs back when pressed, and a fresh sea smell. Avoid fish with sunken eyes, dull appearance, or strong ammonia-like odours. Fresh fish should be consumed within 24 hours of purchase or stored properly in the coldest part of the refrigerator.

Frozen fatty fish can be equally nutritious if frozen shortly after catching. Check packaging is intact without ice crystals, which may indicate thawing and refreezing. Defrost frozen fish in the refrigerator overnight rather than at room temperature to prevent bacterial growth. Tinned fatty fish such as sardines, mackerel, and salmon offer convenient, shelf-stable options. Choose varieties in water, olive oil, or tomato sauce rather than brine to manage sodium intake. Tinned fish retains most omega-3 content and provides softened bones rich in calcium.

For preparation and cooking, fatty fish are versatile and can be grilled, baked, poached, or pan-fried. Grilling and baking are healthier methods that don't require additional fat. Avoid deep-frying, which significantly increases calorie content and may produce harmful compounds. When cooking, ensure fish is thoroughly cooked until steaming hot throughout; the flesh should be opaque and flake easily. Pregnant women should ensure fish is thoroughly cooked to reduce infection risk.

Food safety considerations are particularly important for vulnerable groups. Pregnant women, young children, older adults, and immunocompromised individuals should avoid raw or undercooked fish, including sushi made with fatty fish. These groups should also avoid ready-to-eat smoked fish (including smoked salmon and kippers) unless thoroughly cooked until steaming hot, due to the risk of Listeria infection. When preparing fish at home, use separate chopping boards and utensils to prevent cross-contamination with raw foods.

If you experience symptoms such as nausea, vomiting, diarrhoea, or allergic reactions (rash, swelling, difficulty breathing) after consuming fish, seek medical attention promptly. Call 999 immediately if you experience severe symptoms such as difficulty breathing, throat swelling, or dizziness/collapse, and use a prescribed adrenaline auto-injector if advised to do so. Fish allergies can be serious, and individuals with known allergies should avoid all fish products. For persistent digestive symptoms or concerns about fish consumption and existing health conditions, contact your GP for personalised advice.

Frequently Asked Questions