Do Seed Oils Cause Inflammation? What the Research Actually Shows
Do seed oils cause inflammation? It is one of the most repeated claims in nutrition today: sunflower, soybean, corn and rapeseed oil are said to be "inflammatory", and cutting them out is presented as the quickest way to calm the body down. The claim has a real biological starting point, which is why it sticks. But inflammation can be measured in the blood, and researchers have spent two decades doing exactly that in controlled trials. This article sets out what those trials found, which markers they tracked, where the critics still have a fair point, what the cancer headlines were actually about, and what the British Heart Foundation, EUFIC and Harvard's nutrition researchers conclude, so you can weigh the evidence yourself rather than take anyone's word for it, including ours.
For our own oil, see our Cold-Pressed Single-Estate Extra Virgin Olive Oil - Marrakech (500ml).
The Short Answer
- Controlled trials do not show that seed oils raise inflammation in healthy adults. A 2017 meta-analysis by Su and colleagues in Food & Function pooled 30 randomised trials with 1,377 participants and found no significant effect of eating more linoleic acid, the main omega-6 fat in seed oils, on CRP, IL-6 or TNF-α.
- An earlier systematic review of 15 trials (Johnson and Fritsche, 2012) concluded there was "virtually no evidence" that adding linoleic acid to the diet raises inflammatory markers.
- The theory behind the claim is that linoleic acid becomes arachidonic acid, which feeds inflammatory signals. In trials, changing linoleic acid intake barely moved arachidonic acid levels in the blood.
- The critics are not wrong about everything: a 2017 subgroup analysis hinted that very large increases might nudge CRP up, high omega-6 intake may blunt the effects of omega-3, and oil that is reheated again and again breaks down.
- The cancer headlines of 2025 came from laboratory and tumour-tissue studies. They are interesting biology, not evidence that a bottle of sunflower oil causes cancer in people.
- The BHF, EUFIC and Harvard's Walter Willett all conclude there is no good evidence that seed oils cause inflammation; most agree the bigger concern is the fried and ultra-processed food they often arrive in.
- Choosing olive oil instead is a reasonable preference about taste and processing, not a medical necessity. If a blood test has shown raised inflammation, that is a conversation for your doctor, not a reason to rebuild your kitchen around one oil.
Why Seed Oils Got the Blame: The Omega-6 Theory
Most seed oils are rich in linoleic acid, an omega-6 polyunsaturated fat. The body cannot make it, so it must come from food, and it is used in cell membranes and skin. The concern runs like this: the body can convert some linoleic acid into arachidonic acid, and arachidonic acid is the raw material for prostaglandins and leukotrienes, signalling molecules involved in starting inflammation. Several anti-inflammatory medicines work by blocking that pathway. So, the argument goes, more seed oil means more arachidonic acid, which means more inflammation.
Each step sounds plausible, and the first and last are not in dispute. The pathway is real. Innes and Calder's 2018 review in Prostaglandins, Leukotrienes and Essential Fatty Acids describes arachidonic acid as a precursor to "potent pro-inflammatory mediators". The weak link is the middle step: whether eating more linoleic acid actually increases arachidonic acid, and whether that shows up as measurable inflammation in a living person. That is a testable question, and it has been tested.
Critics also make a broader case. The physician Cate Shanahan's 2024 book Dark Calories says, in its publisher's description, that eight common seed oils lead to chronic disease and drive "inflammatory fat buildup" and "intracellular oxidative stress". Those are the claims this article checks against the trial evidence.
What Randomised Trials Measured: CRP, IL-6 and TNF-α
Inflammation leaves fingerprints in the blood. C-reactive protein (CRP) is the marker most doctors know; interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α) are cytokines that drive the inflammatory response; fibrinogen and adhesion molecules sit further downstream. If seed oils were inflammatory, feeding people more of their main fat should push these up.
Two systematic reviews have pulled the trials together. Johnson and Fritsche's 2012 review in the Journal of the Academy of Nutrition and Dietetics found 15 randomised controlled trials in healthy adults that changed linoleic acid intake and measured inflammation. None reported a significant rise in CRP, fibrinogen, cytokines, adhesion molecules or TNF-α, and the authors concluded there was "virtually no evidence" from such trials that adding linoleic acid increases inflammatory markers. Su and colleagues' 2017 meta-analysis in Food & Function went further, pooling 30 trials and 1,377 participants.
| Marker | What it reflects | Pooled effect of more linoleic acid (Su et al., 2017) |
|---|---|---|
| C-reactive protein (CRP) | General inflammation, made by the liver | No significant change across 16 trials (SMD 0.09; 95% CI −0.05 to 0.24) |
| Interleukin-6 (IL-6) | Signalling cytokine that triggers CRP | No significant change (SMD 0.11; 95% CI −0.07 to 0.29) |
| Tumour necrosis factor-α (TNF-α) | Early inflammatory cytokine | No significant change (SMD −0.01; 95% CI −0.19 to 0.17) |
| MCP-1 and adiponectin | Immune-cell recruitment; metabolic signalling | No significant change |
| Fibrinogen, PAI-1, adhesion molecules | Clotting and blood-vessel inflammation | No significant change |
There is one honest caveat in the same paper, and it matters. Subgroup and meta-regression analyses suggested that in people whose linoleic acid intake rose most sharply, CRP might rise. The authors called this a possibility, not a finding, and some markers rested on few studies. It is a reason for curiosity about very high intakes, not evidence that ordinary use of seed oils is inflammatory.
Does Linoleic Acid Really Turn Into Arachidonic Acid?
The trials help explain why the theory falters. Rett and Whelan's 2011 systematic review in Nutrition & Metabolism looked at what happens to arachidonic acid in the blood when adults on Western-style diets change their linoleic acid intake. Cutting linoleic acid by up to 90%, or raising it up to six-fold, did not significantly change arachidonic acid in plasma or serum phospholipids. The body appears to keep arachidonic acid within a fairly steady range, whatever the frying pan is doing.
Population data point the same way, with the usual limits of observational research. In 2025, Lai and colleagues reported in Nutrients on 2,777 adults from the Framingham Offspring and Omni cohorts, average age 66. People with more linoleic acid in their red blood cells tended to have slightly lower CRP, soluble IL-6 receptor and several other inflammatory markers, and the authors concluded their findings "do not support the hypothesis that omega-6 fatty acids are pro-inflammatory". The correlations were weak, and a cohort cannot prove cause, so this is supporting evidence rather than proof that seed oils calm inflammation.
Where the Critics Have a Point
An even-handed reading of the evidence is not the same as dismissing every concern. Four are worth taking seriously.
Omega-6 and omega-3 compete
Omega-6 and omega-3 fats use the same enzymes. Simopoulos argued in 2002 in Biomedicine & Pharmacotherapy that humans evolved on an omega-6 to omega-3 ratio of roughly 1:1, against 15:1 to 16.7:1 in Western diets. Innes and Calder's review notes evidence that a high omega-6 diet may blunt the anti-inflammatory effects of omega-3. Many experts now focus less on the ratio and more on eating enough omega-3 in absolute terms; EUFIC, for example, points to at least 250–500 mg of EPA and DHA a day.
Oxidised linoleic acid products
Linoleic acid can be oxidised into compounds known as OXLAMs. In a 12-week trial in people with chronic headaches, published in 2012, Ramsden and colleagues found that lowering dietary linoleic acid reduced these compounds in the blood. The authors called for studies of what that means clinically; it has not yet shown an effect on inflammation-related disease.
Oil that is reheated again and again
Fresh oil and fryer oil used for days are not the same food. A 2019 review in Critical Reviews in Food Science and Nutrition by Ganesan, Sukalingam and Xu described how repeatedly heated cooking oils form compounds including polycyclic aromatic hydrocarbons, though much of the evidence it gathered is laboratory and animal work. That is an argument about how oil is used, mostly in commercial frying, and it applies to any oil reheated enough times.
What seed oils usually come with
Most seed oil in Western diets arrives in crisps, takeaways, biscuits and fried food. Researchers on both sides agree that diets heavy in those foods are worth changing. The disagreement is over whether the oil is the cause or the passenger.
Seed Oils and Cancer Headlines: What Those Studies Measured
Two 2025 papers are widely shared as proof that seed oils cause cancer. Both are serious science; neither measured what people ate.
Koundouros and colleagues, writing in Science, described a mechanism by which cells sense linoleic acid through a protein called FABP5, increasing growth signalling, and found higher FABP5 levels in tumours and serum from patients with triple-negative breast cancer than in other subtypes. Soundararajan and colleagues, in Gut, analysed 81 pairs of colorectal tumour and normal tissue samples and found a pro-inflammatory lipid profile in the tumours, with too few of the molecules that normally switch inflammation off.
Both papers deepen our understanding of how fats behave inside cells and tumours. Neither is a dietary trial, and neither shows that people who cook with seed oils develop more cancer. Anyone worried about cancer risk is better served by speaking to their GP about personal and family risk factors than by any single food.
What Health Bodies Say
- British Heart Foundation. In a page updated in February 2026, BHF dietitian Tracy Parker writes that "there is no strong or consistent proof that omega-6 fats directly cause inflammation in humans" and that "there's no need to completely avoid seed oils", while advising moderation because they are high in calories.
- EUFIC. The European Food Information Council's March 2025 explainer concludes that randomised trials do not show linoleic acid raising inflammatory markers, and that "what matters most is the balance of the diet as a whole, not just how much seed oil you eat". It notes the American Heart Association's recommendation of 5–10% of daily calories from omega-6.
- Harvard T.H. Chan School of Public Health. In a February 2025 article, epidemiologist Walter Willett said that of the dozens of studies on omega-6 and inflammation, "about half of them show no effect, while the other half show reduction in inflammatory factors", and called seed oils "basically a very healthy part of a diet".
For the wider picture on mortality trials, the full list of oils and the newest US dietary guidelines, see our seed oils list, which this article deliberately does not repeat.
Scorecard: Seed-Oil Inflammation Claims vs the Evidence
| Claim | What the evidence shows | Verdict |
|---|---|---|
| Seed oils raise inflammation in healthy people | 30 randomised trials pooled: no significant change in CRP, IL-6 or TNF-α (Su et al., 2017) | Not supported |
| Eating linoleic acid floods the body with arachidonic acid | Cutting it by 90% or raising it six-fold barely changed blood arachidonic acid (Rett and Whelan, 2011) | Not supported |
| Very high intakes could raise CRP | A subgroup signal in one meta-analysis, not a confirmed effect | Unresolved |
| Too much omega-6 relative to omega-3 matters | Plausible competition for enzymes; experts now emphasise getting enough omega-3 | Partly supported |
| Repeatedly reheated frying oil is a problem | Breakdown products form with repeated heating, mostly shown in lab and animal work | Reasonable concern |
| Seed oils cause cancer | 2025 studies were on cell signalling and tumour tissue, not diet | Not shown |
What Actually Matters If You Care About Inflammation
If the trials are right, swapping one cooking oil for another is unlikely to move your CRP on its own. The steps with stronger support are less exciting and more useful.
- Look at the whole diet. Fewer deep-fried and ultra-processed foods, more vegetables, pulses, whole grains, nuts and seeds.
- Get enough omega-3. Oily fish is the main source of EPA and DHA; walnuts, flaxseed and rapeseed oil supply the plant omega-3, ALA.
- Do not reuse frying oil for days. At home, fresh oil and sensible temperatures matter more than which plant it came from.
- Choose oils for how you cook and what you enjoy. Our guide to the healthiest cooking oils compares them by use.
- Talk to a clinician about a raised result. A high CRP has many possible causes, and it needs a proper assessment rather than a diet experiment.
Where does that leave olive oil? Botanically it is not a seed oil at all, as our article on whether olive oil is a seed oil explains: it is pressed from the fruit. It is mostly monounsaturated oleic acid and much lower in linoleic acid than sunflower or soybean oil, as our breakdown of olive oil's omega-3, 6 and 9 shows. Extra virgin olive oil also carries polyphenols, which have their own research literature, reviewed in our article on olive oil and inflammation. None of that makes seed oils dangerous; it simply makes extra virgin olive oil a good everyday choice for people who prefer an unrefined, single-ingredient oil.
Why Sidr & Stone
This article does not argue that you must give up seed oils. If you prefer an oil that is pressed rather than refined, with one ingredient and a short journey from tree to bottle, that is what we make. Sidr & Stone's Cold-Pressed Single-Estate Extra Virgin Olive Oil - Marrakech (500ml) comes from olives grown on our own farm on the plains outside Marrakech, Morocco.
- Single-estate: Sidr & Stone's olive oil comes from our own family-owned farm near Marrakech, with every step from tree to bottle under our control and no blending across origins.
- Rain-fed: the trees are not irrigated; they take what the season gives.
- Organically grown: no synthetic fertilisers, pesticides or herbicides are used (not yet certified organic; certification is in progress).
- Single harvest: each batch is a small, limited single-harvest batch, picked when the fruit is ready.
- Cold-pressed: Sidr & Stone's olive oil is extracted mechanically, with no solvents and no refining.
- Unfiltered extra virgin: minimally processed, so it may show natural sediment, which is normal.
- 100% natural: one ingredient, olive oil, with nothing blended in.
- Dark glass with a gold label: the 500ml bottle protects the oil from light.
- 10% of profits to charity: a commitment across every Sidr & Stone product.
- Fulfilment in the UK, EU, and US.
We will not tell you Sidr & Stone is the best olive oil, or that any oil will settle inflammation; that would be exactly the kind of claim this article asks you to look past. What we will say is that our oil is single-estate Moroccan, rain-fed, organically grown and cold-pressed, from a farm we run ourselves.
Frequently Asked Questions
Do seed oils cause inflammation?
Not in the controlled trials so far. A 2017 meta-analysis of 30 randomised trials found that eating more linoleic acid, the main fat in seed oils, did not significantly change CRP, IL-6 or TNF-α in adults.
Why do people say omega-6 is inflammatory?
Because linoleic acid can be converted to arachidonic acid, which the body uses to make inflammatory signals. In trials, though, changing linoleic acid intake had little effect on blood arachidonic acid, and inflammatory markers did not rise.
How can I tell whether my diet is affecting inflammation?
Only a blood test such as CRP, interpreted by a clinician, can show your inflammation levels, and many things besides diet affect it. Speak to your GP or doctor rather than relying on symptoms or online checklists.
Are seed oils worse when used for deep frying?
Any oil reheated repeatedly breaks down and forms new compounds, and reviews raise concern about oil reused many times, much of it from laboratory and animal work. Fresh oil and avoiding long-reused fryer oil is the sensible response.
Is Sidr & Stone's olive oil a seed oil?
No. It is pressed from the olive fruit on our own farm outside Marrakech, cold-pressed, and never solvent-extracted, refined or blended.
Do seed oils cause cancer?
That has not been shown in people. The 2025 studies behind the headlines examined cell signalling and tumour tissue, not what participants ate. If you have concerns about cancer risk, speak to a qualified medical professional.
Where can I buy a single-estate extra virgin olive oil?
Our Cold-Pressed Single-Estate Extra Virgin Olive Oil - Marrakech (500ml) is available to pre-order from the Sidr & Stone website as a limited single-harvest batch, with fulfilment in the UK, EU, and US.
Is olive oil a medicine?
No. Olive oil is a food, not a medicine. It has a long traditional history — including being honoured in the Prophetic Sunnah — and a substantial body of modern research, particularly around polyphenols, cardiovascular health, and the Mediterranean diet pattern. It can be a worthwhile part of a healthy routine, but it does not cure diseases and is not a substitute for medical care. Be cautious of any olive oil marketed with specific disease-cure claims.
Final Thoughts
The idea that seed oils are inflammatory began with a real pathway and a reasonable question. When researchers measured inflammation directly, in dozens of randomised trials, the expected rise in CRP, IL-6 and TNF-α did not appear, and blood arachidonic acid barely moved. The open questions are narrower than the headlines suggest: very high intakes, the balance with omega-3, and oil that has been reheated too many times.
That leaves plenty of room for personal preference without fear. If you would rather cook with an unrefined fruit oil, choose it for its flavour and the way it is made, not because a seed oil in your cupboard is quietly inflaming you. Our Cold-Pressed Single-Estate Extra Virgin Olive Oil - Marrakech (500ml), single-estate, rain-fed and cold-pressed, is available to pre-order now as a limited single-harvest batch, with fulfilment in the UK, EU, and US.
Our extra virgin olive oil is grown organically on our own single-estate farm on the plains outside Marrakech: we control every step from tree to bottle, and no synthetic pesticides, herbicides or fertilisers are used. It is not yet certified organic — certification is in progress, and we will publish it as soon as it comes through.
References
- Johnson GH, Fritsche K. Effect of dietary linoleic acid on markers of inflammation in healthy persons: a systematic review of randomized controlled trials. J Acad Nutr Diet. 2012;112(7):1029-41. PMID: 22889633. doi:10.1016/j.jand.2012.03.029
- Su H, Liu R, Chang M, Huang J, Wang X. Dietary linoleic acid intake and blood inflammatory markers: a systematic review and meta-analysis of randomized controlled trials. Food Funct. 2017;8(9):3091-3103. PMID: 28752873. doi:10.1039/c7fo00433h
- Rett BS, Whelan J. Increasing dietary linoleic acid does not increase tissue arachidonic acid content in adults consuming Western-type diets: a systematic review. Nutr Metab (Lond). 2011;8:36. PMID: 21663641. doi:10.1186/1743-7075-8-36
- Lai HTM, Ryder NA, Tintle NL, Jackson KH, Kris-Etherton PM, Harris WS. Red Blood Cell Omega-6 Fatty Acids and Biomarkers of Inflammation in the Framingham Offspring Study. Nutrients. 2025;17(13):2076. PMID: 40647182. doi:10.3390/nu17132076
- Innes JK, Calder PC. Omega-6 fatty acids and inflammation. Prostaglandins Leukot Essent Fatty Acids. 2018;132:41-48. PMID: 29610056. doi:10.1016/j.plefa.2018.03.004
- Simopoulos AP. The importance of the ratio of omega-6/omega-3 essential fatty acids. Biomed Pharmacother. 2002;56(8):365-379. PMID: 12442909.
- Ramsden CE, et al. Lowering dietary linoleic acid reduces bioactive oxidized linoleic acid metabolites in humans. Prostaglandins Leukot Essent Fatty Acids. 2012;87(4-5):135-141. PMID: 22959954.
- Ganesan K, Sukalingam K, Xu B. Impact of consumption of repeatedly heated cooking oils on the incidence of various cancers - A critical review. Crit Rev Food Sci Nutr. 2019;59(3):488-505. PMID: 28925728.
- Koundouros N, et al. Direct sensing of dietary ω-6 linoleic acid through FABP5-mTORC1 signaling. Science. 2025;387(6739):eadm9805. PMID: 40080571.
- Soundararajan R, et al. Integration of lipidomics with targeted, single cell, and spatial transcriptomics defines an unresolved pro-inflammatory state in colon cancer. Gut. 2025;74(4):586-602. PMID: 39658263.
Disclaimer: This article summarises published research and health-body guidance on seed oils and inflammation at the time of writing; research findings and guidance may change, and readers should check current sources. Quotations from health bodies and researchers are reproduced as published. Olive oil is a food, not a medicine, and is not a substitute for medical treatment of any condition. For any health concern, consult a qualified medical professional.