Are Seed Oils Inflammatory? 30 Trials Found No Rise in Key Markers

Why the idea sounds right

The worry about seed oils rests on a chain of real chemistry, which is why it sounds so convincing.

Seed oils such as cottonseed oil are rich in omega-6 fats.5 The main one in food is linoleic acid, or LA.10 Your body can turn LA into another fat, arachidonic acid (AA), and AA is the raw material for signals that switch inflammation on.68

So the theory runs like this: more seed oil means more LA, more LA means more AA, and more AA means more inflammation.2 One trial team called it "a yet unproven theory" and set out to check it in people.4

To test it, change what people eat, then check their blood for CRP (C-reactive protein), IL-6 (interleukin-6) and TNF-alpha (tumor necrosis factor alpha), proteins researchers use as markers of inflammation.12

What happens when people eat more

A 2012 review found fifteen randomized trials that changed how much LA healthy adults ate.2 None of them found a meaningful change in a wide range of markers, CRP and TNF-alpha included. The authors saw "virtually no evidence" that adding LA to the diet raises inflammation markers.2

In 16 trials that measured CRP, eating more linoleic acid did not change it.From a 2017 meta-analysis in Food Funct

Five years later, a larger meta-analysis (a study that pools the results of many others) took in 30 randomized trials with 1,377 people.1 Eating more LA did not meaningfully change TNF-alpha or IL-6, and in the 16 trials that measured CRP, it did not change CRP either.1

The longest trials point the same way. A 2021 review gathered 83 randomized trials, with 41,751 people, that each ran for at least 24 weeks.3 Results for omega-6 fats were sparse, but where they existed, they suggested little or no effect.3

There is one honest caveat. In the larger meta-analysis, a closer look hinted that people whose LA intake rose the most might see CRP go up.1 That came from a slice of the data, and the overall result stayed flat.1

The butter swap, tested

One trial tested something close to the popular swap of seed oil for butter.4 Researchers put 67 adults who carried extra weight around the belly on one of two diets for 10 weeks, with the same calories. One was high in omega-6 fat from vegetable oils. The other got its fat mainly from butter.4

On the vegetable oil diet, liver fat was lower than on the butter diet, and two inflammation-related markers were lower too.4 The authors found no signs of inflammation from the high omega-6 diet.4

A 2024 trial matched a seed oil against olive oil in 42 adults with high cholesterol. For 8 weeks, study meals gave them about 60% of their energy, with 30% coming from cottonseed oil or olive oil.5 The groups did not differ in CRP, TNF-alpha, IL-6 or IL-1 beta, and neither group's markers changed.5

The weak link in the chain

The theory needs more LA to mean more AA. In people, that step does not hold up well.

A 2011 review of human trials found that cutting LA by up to 90% did not track with changes in blood AA, and raising it up to six fold did not either.6 A 2023 trial came at it from the other side. It fed 62 women with overweight or obesity controlled diets for 12 weeks.7 The low-LA diets brought blood LA down within weeks, but blood AA did not differ between the groups.7 The authors wrote that lowering LA did not bring the changes the theory predicts.7

What blood tests show

Food surveys rely on memory. The amount of LA in your blood is a more objective sign of what you eat.8

In a study of 1,287 healthy men aged 42 to 60, more LA in the blood went with lower CRP.8 Average CRP was 1.86 mg/L in the lowest quarter and 1.37 mg/L in the highest, and men in the top quarter had about half the odds of a high CRP.8 Higher AA was not linked to higher CRP either.8

A 2026 study of 2,133 adults found the same pattern: as blood LA went up, CRP and two other inflammation markers went down.9 The largest look at blood LA pooled 30 long-term studies from 13 countries.10 People with higher LA had lower risks of heart and blood vessel disease, of stroke from a blocked artery, and of dying from heart and blood vessel disease.10

These are observational studies, so they show a link, not proof. Still, if seed oils were quietly inflaming people, you would expect those with the most LA in their blood to look worse. They looked better.

The real open questions

None of this gives every oil, in every form, a free pass.

Oil that is heated again and again. Heating oil above 150°C breaks some of its fat down into possibly harmful compounds.11 In a 2026 trial, 19 healthy men ate one meal made with oil that had been heated at 180°C over 10 days, and one made with fresh oil.11 Their blood vessels responded the same way over the next few hours.11 But that was one meal, not years of eating, and the trial measured blood vessels, fats and sugar, not inflammation markers.11

Ultra-processed foods. A 2025 review mapped 24 studies on these foods and inflammation.12 In adults, 11 of 17 analyses found higher CRP in people who ate more of them.12 Those studies tracked the foods as a whole, so they can't single out the oil or any other ingredient.12

The bottom line

The chain from seed oil to inflammation sounds tidy, but in people it breaks early. Trials that fed people more LA saw their markers stay flat. The butter swap brought no gain. And the people with the most LA in their blood had the lowest CRP.

The claim that seed oils inflame your body is not supported.

If you want food to help with inflammation, look past the bottle in your cupboard. Look at the oil that has been reused all week, and at the packaged foods on the shelf beside it.