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Are Seed Oils Bad for You? What the Evidence Actually Shows

Written by Ration Editorial TeamUpdated July 23, 2026Our editorial process

Key takeaways

  • Seed oils are high in omega-6 linoleic acid, a polyunsaturated fat (PUFA).
  • Controlled trials link replacing saturated fat with these oils to lower LDL cholesterol; claims of harm rest largely on mechanism, not outcomes.
  • The strongest case against them is that they concentrate in ultra-processed foods.

What seed oils are

Seed oils such as soybean, corn, and sunflower oil are high in omega-6 linoleic acid, a polyunsaturated fat. Intake has risen sharply as these oils spread through packaged foods.

These foods carry the most polyunsaturated fat per 100 grams:

Polyunsaturated Fat, g per 100 grams
  1. 1Grapeseed Oil69.9 g / 100 g
  2. 2Flaxseed Oil66.4 g / 100 g
  3. 3Walnut Oil63.3 g / 100 g
  4. 4Poppyseed Oil62.4 g / 100 g
  5. 5Wheat Germ Oil61.7 g / 100 g
  6. 6Tomatoseed Oil53.1 g / 100 g
  7. 7Cottonseed Oil51.9 g / 100 g
  8. 8Soybean Oil50.3 g / 100 g
  9. 9Walnuts49.3 g / 100 g
  10. 10Corn Oil46.9 g / 100 g
Ranked by polyunsaturated fat per 100 grams (so dense, dry foods like flours rank high). Computed live from the Ration database.

What trials show

Randomized trials consistently find that replacing saturated fat with polyunsaturated fat lowers LDL cholesterol.[1] Large cohorts associate higher linoleic acid intake with lower, not higher, heart-disease risk.[2] The popular claim that these oils are inflammatory is not well supported by controlled human data on inflammatory markers.[3]

A 2021 review of controlled feeding trials found that swapping saturated fat for oils higher in linoleic acid, like most seed oils, lowers total cholesterol and LDL cholesterol without raising markers of harm.[4] This supports the idea that the main effect of these oils on heart health runs through cholesterol, not inflammation.

The real issue

The most defensible concern is indirect: seed oils are concentrated in fried and ultra-processed foods. Cutting those improves diet quality regardless of the oil itself.

Bottom line

For most people the oil is not the problem; the ultra-processed foods it rides in are. Whole foods with naturally occurring fats remain the better default.

Compare the PUFA content of any food in the spreadsheet.

Put this to work in your own food log. Track it free with Ration →

Mentioned in this article

Polyunsaturated FatSaturated FatLDL cholesterolUltra-processed foodsSunflower oilCholesterolInflammatory markers

Sources

  1. Mensink RP et al. Effects of dietary fatty acids on serum lipids: meta-analysis. Am J Clin Nutr. 2003. · PMID 12716665
  2. Marklund M et al. Biomarkers of dietary omega-6 fatty acids and CVD. Circulation. 2019. · PMID 31151289
  3. Johnson GH, Fritsche K. Effect of dietary linoleic acid on inflammation. J Acad Nutr Diet. 2012. · PMID 22889633
  4. The Effect of Diet on Cardiovascular Disease and Lipid and Lipoprotein Levels · PMID 33945244

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