Omega-3 and Omega-6

What are omega-3 and omega-6 fatty acids?

Omega-3 and omega-6 are families of polyunsaturated fatty acids (PUFAs). A type of dietary fat distinguished by the presence of multiple double bonds in their carbon chain. The numbers ("3" and "6") refer to where the first double bond occurs from the methyl (omega) end of the molecule.

Unlike saturated fats and monounsaturated fats, the body cannot synthesise the key members of the omega-3 and omega-6 families from scratch. They must be obtained from food. This is why they are called essential fatty acids.

Both types are required for normal biological function. They are structural components of cell membranes throughout the body, they serve as precursors to hormone-like signalling molecules called eicosanoids, and they influence gene expression, inflammation, immune function, and the functioning of the brain, eyes, and cardiovascular system.

Why the ratio matters

Omega-3 and omega-6 fatty acids compete for the same enzymes in metabolic pathways. When one is consumed in large excess relative to the other, it can dominate those pathways and alter the balance of signalling molecules produced. A very high omega-6 to omega-3 ratio shifts the balance of eicosanoids towards those that promote inflammation and blood clotting, at the expense of those with anti-inflammatory and anti-clotting properties. This is the basis of the "omega-6/omega-3 ratio" concept.

It is important to be precise here: the problem is not that omega-6 is inherently harmful. It is that excessive intake of omega-6 relative to a low omega-3 intake creates an unfavourable metabolic balance. Increasing omega-3 restores the balance. Simply removing omega-6 from the diet is not the solution, and the evidence does not support it.

The three types of omega-3

There are three main dietary omega-3 fatty acids, and understanding the differences between them matters practically.

Omega-6. Essential, but often overconsumed

The main omega-6: linoleic acid (LA)

Linoleic acid is the primary dietary omega-6 and, like ALA, it is an essential fatty acid that must come from food. It is found in most vegetable and seed oils. Sunflower oil, corn oil, soybean oil, and safflower oil are particularly high in LA. Nuts (especially walnuts and pine nuts) and seeds also contain meaningful amounts.

The body converts LA into longer-chain omega-6 fatty acids, including arachidonic acid (AA). AA can be converted into pro-inflammatory eicosanoids, which is the basis of the claim that omega-6 causes inflammation.

Does omega-6 actually cause inflammation? The evidence

This is one of the most actively debated topics in nutrition science, and one where the popular discourse has significantly diverged from the scientific evidence. The claim is that linoleic acid is converted to arachidonic acid, which produces pro-inflammatory compounds, therefore high LA intake means more inflammation.

What the evidence actually shows:

• Multiple controlled studies have found that increasing dietary linoleic acid does NOT significantly increase arachidonic acid levels in blood or tissues. One controlled study increased dietary LA by 551% without a significant change in plasma AA.
• Clinical trials looking at inflammatory biomarkers (CRP, IL-6, TNF-α) consistently find that linoleic acid either has no effect or a mildly anti-inflammatory effect on these markers, not a pro-inflammatory one.
• A cross-sectional study from the Framingham Offspring Study (2025) found that higher red blood cell linoleic acid content was associated with lower levels of IL-6 and CRP. The opposite of what the inflammation hypothesis predicts.
• The British Heart Foundation, Johns Hopkins Bloomberg School of Public Health, the European Food Information Council, and the University of Queensland all conclude that there is no strong or consistent evidence that seed oils (or their linoleic acid content) cause inflammation at typical dietary levels.

The nuanced picture: seed oils are not the cause of modern chronic disease. They are neutral to mildly beneficial on their own, and the real problem is that people are not eating enough omega-3, not that they are eating too much omega-6.

The one genuine concern with seed oils

High-heat cooking with polyunsaturated oils (particularly frying at very high temperatures) can generate oxidation products. This is a real but often overstated concern. Cooking at moderate temperatures with any quality oil, including sunflower oil, is not a health hazard. For very high-heat cooking (deep frying, wok cooking), oils with higher smoke points and greater heat stability, such as rapeseed oil or refined olive oil, are preferable to cold-pressed oils with lower smoke points.

The omega-6/omega-3 ratio. Why the imbalance matters

The estimated omega-6/omega-3 ratio in traditional and ancestral diets was approximately 1:1 to 4:1. In most Western diets today, including UK diets, it has shifted to somewhere between 15:1 and 20:1. This shift occurred primarily because:

1. The consumption of omega-6-rich vegetable oils increased dramatically in the 20th century. They replaced animal fats in cooking and food manufacturing.
2. The consumption of oily fish (the primary source of EPA and DHA) declined.
3. Livestock and farmed fish are now fed grain-based diets rather than grass or marine feed, reducing the omega-3 content of the meat and farmed fish that people eat.

The practical implication: you do not need to remove omega-6 from your diet. You need to substantially increase your omega-3 intake.

Omega-3 and health. What the evidence shows

Cardiovascular health

Long-term prospective cohort studies consistently find that higher intakes of fish, oily fish, and marine omega-3s are associated with lower risk of cardiovascular disease, coronary heart disease, and cardiovascular mortality. Mechanisms include reduced triglycerides (3 to 4g/day can reduce triglycerides by 20 to 50% in those with elevated levels), modestly reduced blood pressure, improved endothelial function, anti-arrhythmic effects, reduced platelet aggregation, and resolvin/protectin-driven anti-inflammatory effects.

The randomised controlled trial evidence for supplementation is more mixed than the observational evidence. NICE does not currently recommend omega-3 supplements routinely for cardiovascular disease prevention in the general population. The NHS does recommend two portions of fish per week, one oily, for cardiovascular benefit from food.

Brain health and cognitive function

DHA is structurally essential for the brain. Lower DHA levels are consistently associated with worse cognitive function and higher dementia risk in observational studies. Populations with higher fish consumption have lower rates of cognitive decline and dementia in large epidemiological studies.

Eye health

DHA is concentrated in the retina and is essential for visual function. Adequate DHA intake during pregnancy and infancy is critical for visual development. In adults, higher omega-3 intake is associated with lower risk of age-related macular degeneration (AMD), a leading cause of blindness in older UK adults.

Inflammation and immune function

EPA and DHA are converted into resolvins, protectins, and maresins. Lipid mediators that actively resolve (not just prevent) inflammation. This is mechanistically distinct from most anti-inflammatory drugs, which block inflammatory pathways without resolving them. EPA and DHA supplementation has shown symptom benefit in inflammatory conditions including rheumatoid arthritis.

Mental health

EPA-rich omega-3 supplementation has the strongest evidence for antidepressant effects, and low oily fish consumption is consistently associated with higher rates of depression and anxiety across populations. See the food and mental health guide for the detail.

What about omega-3 supplements?

Fish oil capsules

Fish oil supplements are the most common omega-3 supplement and are a practical option when dietary intake of oily fish is consistently low. They provide pre-formed EPA and DHA. Quality varies considerably between products. Look for supplements that declare EPA and DHA content separately (not just "omega-3"), as some products are largely ALA from less concentrated sources.

Standard fish oil supplements typically provide 180mg EPA + 120mg DHA per capsule. Most UK adults who eat little or no oily fish would benefit from 2 to 3 standard capsules daily to approach the 450mg EPA+DHA per day SACN target.

When supplements are clearly warranted

• People who eat no oily fish
• Vegans and vegetarians (use algae-derived instead)
• Pregnant women who eat limited oily fish
• People with elevated triglycerides, under medical guidance
• Potentially people with clinical depression, EPA-enriched formulations (see mental health guide)

NICE and high-dose guidance

NICE does not routinely recommend omega-3 supplements for primary cardiovascular disease prevention in the general population. Evidence is stronger for secondary prevention (after a cardiovascular event) and for specific high-risk patients. If you have been advised by a GP or cardiologist to take omega-3 supplements, follow that advice.

Doses above 3g per day can increase bleeding risk and interact with anticoagulant medications (warfarin, aspirin, direct oral anticoagulants). Anyone taking prescribed blood-thinning medication should discuss omega-3 supplementation with their GP before starting.

Practical steps to improve your omega-3 balance

1. Eat oily fish at least once a week, ideally twice. The single most impactful change for most UK adults. One 140g portion of mackerel, salmon, sardines, herring, or trout provides 2,000 to 3,000mg of EPA+DHA. Affordable options: tinned mackerel (~60 to 80p per tin), tinned sardines, frozen salmon fillets, herring. Tinned and frozen oily fish are nutritionally equivalent to fresh.
2. Remember: tinned tuna is not oily fish for omega-3. Switch some of those occasions to tinned mackerel or sardines. Better omega-3, similar convenience, often cheaper.
3. Add ALA-rich plant foods daily. Ground flaxseed in porridge, chia seeds in yogurt, a small handful of walnuts, or rapeseed oil as your primary cooking oil. ALA does not fully replace marine EPA/DHA, but it contributes meaningfully and has independent benefits.
4. Use rapeseed oil for cooking and olive oil for cold use. Rapeseed has the best omega-6:omega-3 ratio of any widely available UK cooking oil, a decent smoke point, mild flavour, and is UK-grown. Extra virgin olive oil is excellent for dressings and lower-heat cooking.
5. Consider a supplement if you eat little or no oily fish. Aim for 250 to 500mg combined EPA+DHA per day from supplementation. Vegans and vegetarians should use an algae-derived version.
6. Reduce ultra-processed foods. Many UPFs are made with large quantities of cheap omega-6-heavy oils. Reducing UPF consumption automatically reduces excess omega-6 while opening space in the diet for whole foods with better fatty acid profiles. See ultra-processed foods for the broader picture.

Omega-3 during pregnancy. Special considerations

DHA is particularly critical during the third trimester of pregnancy and in the first two years of life, when the brain and eyes develop most rapidly. Babies are born with DHA levels that reflect maternal intake during pregnancy.

The EFSA recommends an additional 100 to 200mg of DHA per day during pregnancy, in addition to a normal adult intake.

The seed oil controversy. A plain-English summary

The "seed oils are toxic" discourse, which became prominent on social media platforms around 2022 to 2024, makes several claims that are not well supported by the scientific evidence.

What is well-supported: the omega-6:omega-3 ratio in Western diets is too high, primarily because omega-3 intake (from oily fish) is too low. The evidence-based response is to eat more omega-3, not to demonise omega-6.

The British Heart Foundation's conclusion (April 2025): "There is a lack of conclusive evidence that seed oils increase inflammation and raise the risk of cardiovascular disease."

Key statistics at a glance