Do seed oils cause chronic diseases?

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 cause a rise in chronic diseases, including cardiovascular disease and type 2 diabetes? Let’s debunk this myth.

Is eating seed oils bad for you?

No, eating seed oils is not bad for you. Our consumption of seed oils has indeed increased over the past decades. Some argue that this increased consumption has coincided with the rise of a variety of chronic diseases, thus seed oils must be to blame. However, this is an association, not causation, as it ignores other possible factors that increase our disease risk.

Seed oils are typically found in foods such as packaged salty snacks, pastries, cakes, and French fries all of which also tend to be high in salt and sugar which we should limit our consumption of because they increase our chronic disease risk. We’ve also become more sedentary, contributing to a rise in chronic diseases. So, the fact that seed oils consumption is rising at the same time as the incidence of chronic diseases doesn’t necessarily mean that one is causing the other.

Research shows a consistent favourable effect from increasing omega-6 fatty acids, which is a good marker of seed oil intake, on cardiovascular risk, both in interventional studies and in observational studies, increasing the certainty of evidence.^1-4 Omega-6 polyunsaturated fatty acids (PUFAs) work, for example, by reducing LDL cholesterol, a type of cholesterol known to increase our risk of cardiovascular disease. The European Food Safety Authority (EFSA) approved this claim stating that “linoleic acid contributes to the maintenance of normal blood cholesterol levels.”⁵ This beneficial effect is obtained with a daily intake of 10 g of linoleic acid, which is equal to, for example, about 1.5 tablespoons of sunflower oil or soybean oil or about 3.5 tablespoons of rapeseed oil.⁶ This represents about 8%, 9% and 23% of daily calories (for a 2,000 kcal diet), respectively.

Higher levels of omega-6 PUFAs, and specifically linoleic acid, also improve long-term glycaemic control (blood sugar control) and insulin resistance, important factors in the development and management of type 2 diabetes.^1,7

Why are seed oils not bad for you?

Studies used to claim that seed oils increase chronic disease risk have certain issues in their methodology that weaken their findings. For instance, the Sydney Diet-Heart Study conducted in the 1960s which found that men who increased their omega-6 intake through seed oils had a higher risk of cardiovascular events had an important caveat.⁸ Much of the seed oil that was eaten back then was in the form of margarine containing trans fats, which are consensually known to significantly increase disease risk (and now have been largely removed from food products in the EU as a result). As such, the presence of trans fats may have probably been the reason for the higher risk of cardiovascular events. Additionally, the study had too few participants, too short of a duration, and other confounding factors present which weaken the quality of the findings.

Similarly, the Minnesota Coronary Experiment, comparing a diet designed to be high in PUFA to a control diet high in saturated fat on coronary heart disease outcomes, had certain flaws.⁹ Participants didn’t consistently follow the diets assigned and their findings were statistically insignificant (they didn’t show any meaningful difference between the two diets).

Another study used to claim that seed oils are harmful to our health is the Rose Corn Oil Trial, comparing a corn oil and olive oil group to a control group of habitual diet.¹⁰ With just 26 participants per group, this is too small to be considered conclusive evidence. Additionally, the presence of trans fats again complicates its interpretation.

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.^11,12

Takeaways

• The fats in seed oils, including omega-6 PUFAs, are essential to health, and there is no strong evidence that they cause chronic disease.
• Correlation is not causation. While the rise in chronic diseases coincides with higher seed oil consumption, this doesn’t mean seed oils are to blame. Other factors, like sedentary lifestyles and diets high in saturated fat, salt, and sugar also play significant roles.
• When deciding whether to limit seed oils completely from your diet, consider the ’whole’ product, not just the fact that they contain seed oils. Many foods that include seed oils also tend to be high in salt and sugar, which we should limit in our diet.
• Seed oils can lower LDL cholesterol, a key risk factor for heart disease, and have been linked to better blood sugar control and reduced insulin resistance, which are crucial for preventing and managing type 2 diabetes.
• Chronic diseases are influenced by multiple factors, including genetic, physiological, environmental, and behavioural factors. By addressing the four common modifiable risk factors (an unhealthy diet, physical inactivity, tobacco use, and alcohol use) we can significantly cut down our chronic disease risk.
• 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.^11,12
• EFSA suggests that at least 4% of our daily calorie intake should come from omega-6 fats. Current research shows no clear evidence that consuming omega-6 fats harms health or contributes to diet-related diseases.¹³

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

Do seed oils cause inflammation?

Does the processing of seed oils pose a health risk?

Do seed oils promote oxidative stress?

References

1. Marangoni F, Agostoni C, Borghi C, Catapano AL, Cena H, Ghiselli A, et al. (2020). Dietary linoleic acid and human health: Focus on cardiovascular and cardiometabolic effects. Atherosclerosis 292:90-98.
2. Sacks FM, Lichtenstein AH, Wu JH, Appel LJ, Creager MA, Kris-Etherton PM, et al. (2017). Dietary fats and cardiovascular disease: a presidential advisory from the American Heart Association. Circulation 136(3):e1-e23.
3. Marklund M, Wu JH, Imamura F, Del Gobbo LC, Fretts A, De Goede J, et al.; Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Fatty Acids and Outcomes Research Consortium (FORCE). (2019). Biomarkers of dietary omega-6 fatty acids and i
4. Djuricic I, Calder PC. (2021). Beneficial outcomes of omega-6 and omega-3 polyunsaturated fatty acids on human health: An update for 2021. Nutrients 13(7):2421. https://doi.org/10.3390/nu13072421
5. European Commission. (2012). Food and Feed Information Portal Database. Accessed 22 January 2025.
6. Dutch Food Composition Database (NEVO). (2021). NEVO-online version 2021/7.1. Accessed 22 January 2025.
7. Okuyama H, Langsjoen PH, Ohara N, et al. (2016). Medicines and vegetable oils as hidden causes of cardiovascular disease and diabetes. Annals of Nutrition & Metabolism. DOI: 10.1159/000446704.
8. Ramsden CE, Zamora D, Faurot K, Majchrzak S, Hibbeln J. (2013). The Sydney Diet Heart Study: A randomized controlled trial of linoleic acid for secondary prevention of coronary heart disease and death.
9. Ramsden CE, Zamora D, Majchrzak-Hong S, Faurot KR, Broste SK, Frantz RP, et al. (2016). Re-evaluation of the traditional diet-heart hypothesis: Analysis of recovered data from Minnesota Coronary Experiment (1968-73). BMJ 353:i1246.
10. Rose GA, Thomson WB, Williams RT. (1965). Corn oil in treatment of ischaemic heart disease. British Medical Journal 1(5449):1531–1533. https://doi.org/10.1136/bmj.1.5449.1531
11. World Health Organisation (WHO)., 2018. Draft Guidelines: Saturated fatty acid and trans-fatty acid intake for adults and children.
12. 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 Pract
13. European Food Safety Authority (EFSA). (2017). Dietary reference values for nutrients summary report. EFSA Journal 14(12):e15121E.