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Do seed oils cause inflammation? What two 2026 trials found

Neither trial shows it: one found no change in inflammation markers after four weeks of soybean oil, and the other found a high linoleic-acid diet shifted omega-3 and omega-6 markers in the blood without measuring any disease.

Published · Sources checked 27 Sep 2026 · By Assize Index

Three glass bottles of seed oil behind bowls of sunflower seeds, rapeseed, and soybeans.

Summary

Background.
Seed oils are blamed online for inflammation, mostly because of their linoleic acid, an omega-6 fat.
What we found.
A small 4-week crossover found no change in inflammation markers on soybean oil versus palm oil. A 12-week trial in 52 adults found a high linoleic-acid diet lowered blood omega-3s (EPA, ETA) and shifted related signaling molecules.
What it means.
Blood markers moved in one trial and inflammation markers didn’t in the other. Neither measured heart disease, diabetes, or any other disease outcome.

Trial 1: soybean vs palm oil, 4 weeks

Yang et al., Current Developments in Nutrition, 20261. A small pilot study; the trial registry lists 16 planned participants3.

  • Who: adults with overweight or obesity, in a secondary analysis of the pilot.
  • What: 30 g a day of soybean oil or palm oil, baked into snack foods. Each person had both, 4 weeks each, with a 2-week break between.
  • Found: no significant change in inflammation markers (CRP, IL-6 and others) or oxidized LDL on either oil. IL-6 trended lower on soybean oil, but not significantly (p = 0.09). Arachidonic acid in red blood cells, the omega-6 most seed-oil worries center on, fell after soybean oil.
  • Limits: a pilot this size, run for four weeks, is built to test feasibility. “No significant change” in a trial this small is weak evidence of no effect.

Trial 2: low vs high linoleic acid, 12 weeks

Sergeant et al., Nutrients, June 20262. First posted as a preprint in April; this is the published version.

  • Who: 80 healthy adults enrolled; 52 completed.
  • What: a diet with 2.5% of energy from linoleic acid, the main fat in most seed oils, against one with 10%. Double-blind.
  • Found: the high linoleic-acid diet lowered blood EPA and ETA, both omega-3s, and DPA was lower at weeks 4 and 8. Oxylipins, signaling molecules made from these fats, shifted toward the ones made from arachidonic acid. Arachidonic acid itself didn’t change, and DHA drifted down without reaching significance.
  • Limits: these are blood markers, not health outcomes, and 28 of the 80 people who started didn’t finish. Whether the shift matters for disease is a question the trial doesn’t answer.

Reading them together

The two trials measured different things. The first looked for inflammation and didn’t find it. The second looked at the omega-3 and omega-6 balance in blood and found a shift. Both can be true at once. What neither shows: that seed oils cause disease, or that they prevent it.

For scale, linoleic acid per 100 g on our table4:

OilLinoleic acid, g per 100 g
Sunflower, high-linoleic65.7
Soybean50.9
Canola17.8
Extra-virgin olive8.4
Sunflower, high-oleic3.6

Table impact

None. Our oil recipes already treat omega-6 as a small balance term, not a verdict: 0.10 of the salad recipe and 0.08 of the heart-lean recipe. The high-heat recipe scores total polyunsaturated fat for chemical stability under heat, not linoleic acid alone. Neither trial measured a health outcome, so neither changes a weight. If trials with health outcomes arrive, the change goes through Methods and gets explained here.

On our tables

References

  1. Yang C.-T., Cole R.M., Colombo E., Angelotti A., Ni A., Belury M.A. Foods fortified with soybean or palm oil show no effect on inflammation or oxidized low-density lipoprotein in adults with overweight or obesity. Current Developments in Nutrition 10(2): 107635, 2026. doi.org/10.1016/j.cdnut.2025.107635
  2. Sergeant S., et al. Nutrients 18(11): 1814, published 4 June 2026 (NCT02962128). First posted on medRxiv, 10 April 2026, as “High dietary linoleic acid intake suppresses eicosapentaenoic acid status and shifts oxylipin metabolism towards arachidonic acid in healthy adults: a randomized controlled trial.” doi.org/10.3390/nu18111814
  3. ClinicalTrials.gov. NCT04975763: soybean or palm oil in snack foods, adults with overweight or obesity. Registry record, accessed 2026. clinicaltrials.gov/study/NCT04975763
  4. USDA FoodData Central, SR Legacy and Foundation fatty-acid values, as cited on each oil row of our table. fdc.nal.usda.gov/

Declaration of interests

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Assize Index. Do seed oils cause inflammation? What two 2026 trials found. Behind the Table, 5 Oct 2026. assizeindex.com/behind-the-table/seed-oils-inflammation-2026-trials Reuse terms

Data, not medical advice. For decisions about your own health, talk with a clinician.