Does the processing of seed oils pose a health risk?

Seed oils are oils extracted from the seeds of various plants. You’ll recognise them as rapeseed (or canola), corn (maize), cottonseed, grapeseed, soybean, sunflower, safflower, and rice bran oil. They’re affordable, have a high smoke point (meaning they are stable at high temperatures, which makes them suitable for frying), and many are rich in vitamins E and K. So, why are many on social media advocating to ditch seed oils because they supposedly undergo heavy processing which can result in the formation of potentially harmful compounds, posing a health risk? Let’s debunk this myth.

How are seed oils made?

A common misconception is that seed oils are heavily processed through methods like bleaching and deodorising, leading to the formation of harmful compounds in the final product that pose health risks. While seed oils do undergo refining to improve their shelf-life, taste, and stability, modern processing techniques are designed to ensure both safety and quality.

The process typically involves the use of heat and solvents like hexane to maximise the extraction of oil from the seeds and remove undesirable minor components that you might find in the oil.¹ Some critics argue that these methods introduce harmful chemicals and turn polyunsaturated fatty acids (PUFAs) that are present in seed oils into harmful trans fats, but the reality is different.

Is the processing of seed oils harmful to us?

Nowadays, improved manufacturing practices have significantly reduced trans fats in refined oils, and the trace amounts of hexane left in the oil after processing are not considered a health risk.^1,2 Risk assessment agencies like the European Food Safety Authority (EFSA) regularly monitor the levels of trans fats and contaminants such as glycidyl ester, 3-MCPD-esters, ensuring that oils meet safety standards before reaching consumers. The heating involved in oil refining is brief and controlled, producing very few trans fats — far fewer than are found in naturally occurring amounts in products like butter or milk.³

A bigger concern arises when seed oils are repeatedly heated at high temperatures, such as in deep-frying. Overheating oils can lead to the formation of potentially harmful trans fats and other cancer-causing compounds.^4,5 However, this issue is more relevant in industrial settings like restaurants with infrequent oil changes, where Good Manufacturing Practices should be implemented, rather than in typical home cooking. Overall, when used appropriately, seed oils do not pose significant health risks, even with the refining processes they undergo.

For those concerned about processing, cold-pressed and expeller-pressed oils, which are produced without heat or chemicals, are available as alternatives, though they tend to be more expensive.

Takeaways

• Seed oils are processed to improve taste and shelf-life, but modern techniques are designed to maintain safety and minimise harmful compounds like trans fats and chemical residues.
• Refined seed oils today contain very low levels of trans fats, far less than naturally found in butter or milk. Regulations ensure they meet strict safety standards.
• The small amounts of hexane or other solvents left after refining seed oils are considered safe by food safety authorities, such as EFSA.
• When used appropriately and not repeatedly overheated, seed oils are safe for home cooking and a healthy part of a balanced diet.
• Most dietary guidelines and international and European health bodies, including the World Health Organization and the European Society of Cardiology, recommend we aim to get less than 10% of our total daily energy from saturated fats (e.g., found in butter, palm oil, and coconut oil) to reduce our chronic disease risk and reductions should be achieved by replacing them with unsaturated fats, particularly polyunsaturated fats found in soybean, rapeseed (canola), corn, safflower, and sunflower oil.^6,7

This article is part of a series on seed oil myths:

Do seed oils cause inflammation?

Do seed oils cause chronic diseases?

Do seed oils promote oxidative stress?

References

1. European Food Safety Authority (EFSA), Comandella D, Bignami M, Fürst P, Grob K, Mengelers M, et al. (2024). Technical Report on the need for re-evaluation of the safety of hexane used as an extraction solvent in the production of foodstuffs and food in
2. European Parliament. (2016). Trans fats - overview of recent developments. Accessed 22 January 2025.
3. European Food Safety Authority (EFSA). (2004). Opinion of the Scientific Panel on Dietetic Products, Nutrition and Allergies [NDA] related to the presence of trans fatty acids in foods and the effect on human health of the consumption of trans fatty aci
4. Bhat S, Maganja D, Huang L, Wu JH, Marklund M. (2022). Influence of heating during cooking on trans fatty acid content of edible oils: A systematic review and meta-analysis. Nutrients 14(7):1489.
5. Ganesan K, Sukalingam K, Xu B. (2019). Impact of consumption of repeatedly heated cooking oils on the incidence of various cancers: A critical review. Critical Reviews in Food Science and Nutrition 59(3):488-505.
6. World Health Organisation (WHO)., 2018. Draft Guidelines: Saturated fatty acid and trans-fatty acid intake for adults and children.
7. Piepoli, Massimo F., et al. "2016 European Guidelines on cardiovascular disease prevention in clinical practice: The Sixth Joint Task Force of the European Society of Cardiology and Other Societies on Cardiovascular Disease Prevention in Clinical Practi