Are Seed Oils Bad for You? What the research Actually Says (2026)

What are seed oils, and why are people avoiding them?

Seed oils are oils pressed or extracted from plant seeds: in the UK that mostly means rapeseed oil (often sold simply as "vegetable oil") and sunflower oil, plus corn, soya, safflower, cottonseed, grapeseed and sesame. Olive and avocado oil come from the fruit, so they are not seed oils, although they are often lumped together online.

The "seed oil free" movement has grown fast on social media and in some restaurants. To weigh it fairly, we split it into the separate claims it makes and graded each one.

What it claims

Advocates of cutting seed oils usually argue that:

1. Omega-6 linoleic acid drives inflammation. Seed oils are rich in linoleic acid (an omega-6 fat), which the body can convert into compounds involved in inflammation.
2. They raise heart disease risk. The official advice to replace saturated fat with polyunsaturated oils was based on incomplete trials, and recovered data from two old trials suggest harm.
3. They oxidise when heated. Polyunsaturated fats break down at frying temperatures and form aldehydes (reactive breakdown products).
4. They are industrially processed with solvents (hexane) and high heat, so they leave harmful residues.
5. They are behind rising obesity and chronic disease, because seed oil intake rose over the same decades.

What the evidence shows

Do seed oils cause inflammation?

This is the most repeated claim and the weakest. A systematic review of 15 randomised controlled trials in healthy adults found that eating more linoleic acid did not raise blood markers of inflammation such as C-reactive protein, cytokines or fibrinogen (Johnson and Fritsche 2012). The body tightly controls how much linoleic acid becomes arachidonic acid, the precursor of inflammatory signals. The British Heart Foundation reached the same conclusion in its 2026 review of the claims.

Do seed oils raise or lower heart disease risk?

Most of the evidence points to lower risk when seed oils replace saturated fat:

• Randomised trials of cutting saturated fat. The 2020 Cochrane review (15 trials, 56,675 people) found that reducing saturated fat cut combined cardiovascular events by 17%, with greater benefit the more cholesterol fell. It found little or no effect on total deaths (Hooper et al. 2020).
• Cohort studies of linoleic acid. Across 13 cohorts and 310,602 people, the highest linoleic acid intakes were linked to 15% fewer coronary events and 21% fewer coronary deaths (Farvid et al. 2014). Blood-level studies, which avoid relying on food diaries, found the same direction across 30 cohorts (Marklund et al. 2019).
• Expert reviews. The American Heart Association advisory and the UK SACN report on saturated fats both recommend replacing saturated fat with unsaturated fats.

What about the Sydney and Minnesota trials?

This is the strongest part of the case against seed oils, and it deserves a fair hearing. Researchers at the US National Institutes of Health recovered unpublished data from two trials:

• Sydney Diet Heart Study (1966 to 1973): men who had already had a heart event were told to replace saturated fat with safflower oil and safflower margarine. Deaths were higher in the intervention group (17.6% vs 11.8%) (Ramsden et al. 2013).
• Minnesota Coronary Experiment (1968 to 1973): a corn oil diet lowered cholesterol by about 14% but did not lower deaths, and in a meta-analysis of five similar trials there was no benefit on heart deaths (Ramsden et al. 2016).

The fair counterpoints, raised by the AHA advisory and others, are that the margarines used at the time contained trans fats (now known to be harmful), many Minnesota participants were in the trial for under a year, and these trials used oils very high in linoleic acid with almost no omega-3. The 2018 Cochrane review of omega-6 trials found little or no difference either way in deaths or heart events, with low-quality evidence (Hooper et al. 2018). Our reading: these trials show that more omega-6 is not automatically better, but they do not show that ordinary use of rapeseed oil (which is also rich in omega-3 and monounsaturated fat) harms the heart.

Does heating seed oils create harmful compounds?

Yes, to a degree. Polyunsaturated fats are more prone to oxidation than saturated or monounsaturated fats, and lab studies show that sunflower and corn oil form more aldehydes than olive oil or animal fats during prolonged frying (Grootveld et al. 2021). What we do not have are good human studies showing that home cooking with fresh oil harms health. The practical takeaway is narrow: do not reuse oil many times for deep frying, and for high-heat frying rapeseed or olive oil (more monounsaturated) are better choices than sunflower or corn oil.

What about solvents and processing?

Most refined seed oils are extracted with hexane, which is then removed during refining. Residues are regulated under food law and the BHF notes they are strictly limited. If you prefer to avoid solvent extraction entirely, cold-pressed rapeseed oil is widely available in the UK and costs only a little more.

Are seed oils behind obesity and chronic disease?

Seed oil intake rose alongside ultra-processed food, fast food and total calories, so it is hard to separate them. In a controlled inpatient trial, people ate about 500 kcal a day more on an ultra-processed diet than on an unprocessed one matched for fat, sugar and fibre (Hall et al. 2019). That points to the overall food pattern, not the oil type, as the bigger lever. Cutting seed oils often helps people simply because it means cutting crisps, fried takeaways and packaged snacks.

Who might reasonably cut back on seed oils?

• People who eat a lot of deep-fried takeaway food, where oil is reused many times.
• Anyone whose diet is high in ultra-processed snacks: cutting those will reduce seed oil intake and calories together.
• People who prefer to cook with extra virgin olive oil, which has the strongest overall evidence of any fat (for example in Mediterranean diet trials).

Who should be careful about going "seed oil free"?

• Anyone with high LDL cholesterol, heart disease or diabetes. Replacing seed oils with butter, ghee, lard or tallow will usually raise LDL. The NHS advises no more than 30g of saturated fat a day for men and 20g for women.
• People on statins or other cholesterol treatment: speak to your GP or a dietitian before changing your main cooking fat.
• Anyone cutting food groups based on social media: check the source. Many seed oil claims online come from people selling alternative fats.

If you want to cut back: what to look for

• For everyday cooking: extra virgin olive oil or cold-pressed rapeseed oil.
• For high-heat frying: fresh rapeseed or olive oil, not reused oil. Avoid repeated deep frying in sunflower or corn oil.
• For baking and spreads: if you swap margarine for butter, keep portions small.
• Read labels on packaged foods, but focus on how processed the food is rather than which oil appears in the ingredients list.

We have not recommended specific products on this page because the evidence is about the overall diet, not a brand.

Bottom line

Seed oils are not the hidden poison social media suggests. The best evidence (Cochrane reviews, large cohorts and blood biomarker studies) links swapping saturated fat for unsaturated oils with fewer heart attacks, and linoleic acid does not raise inflammation in trials. The recovered Sydney and Minnesota data are a fair reason not to load up on omega-6 alone, and repeated deep frying is worth avoiding. For most UK households, cooking with olive or rapeseed oil and eating fewer ultra-processed foods is the evidence-backed middle ground.