The Not So Seedy Truth About Seed Oils

If you’ve been confused about seed oils in recent years, you’re not alone. A small but growing minority, as part of a broader anti-science platform, has outspokenly perpetuated misleading claims that seed oils –– oils that come from the seeds of plants –– are harmful to health. These seed oils are known by critics as the “Hateful Eight” and include canola (rapeseed), corn, cottonseed, soybean, sunflower, safflower, grapeseed, and rice bran oils. 

However, no scientific research has offered any conclusive evidence to prove this idea that seed oils have adverse health effects. In fact, there is clear scientific evidence that not only is consuming seed oils not harmful to health (1), but that seed oils can actually be beneficial for cardiovascular health when they’re replacing saturated fat in the diet (2,3,4). 

So where did this misinformation come from? Let’s press in.

What are Seed Oils?

First, what exactly is seed oil? A seed oil is a type of vegetable oil that is extracted from the seeds (rather than the pulp or fruit) of plants - for example, sunflower oil is a seed oil because it is extracted from sunflower seeds, while olive oil is not a seed oil because it is extracted from whole olives. Seed oils are also characterized by their relatively high contents of polyunsaturated fatty acids – particularly omega-6 fatty acids, like linoleic acid. Linoleic acid is one of the essential unsaturated fatty acids humans need in our diets. The other type of essential polyunsaturated fatty acid is the omega 3 fatty acids, which are found in foods like fatty fish, eggs, and flaxseeds. There are also some seed oils that are considered “high-oleic” – meaning, they have a high concentration of oleic acid, which is a monounsaturated fatty acid. One common example is high-oleic sunflower oil, which we use in Impossible products to give our meat its juiciness and sizzle.

By contrast, saturated fatty acids are mostly found in animal-based foods, like red and processed meats, cheese, lard, and tallow. Overwhelming scientific evidence has shown that excess consumption of saturated fats is linked to elevated LDL cholesterol levels and increased risk of cardiovascular diseases (2). Therefore, it is universally agreed upon by public health authorities that saturated fat intake should be limited and replaced by unsaturated fat intake (4). As the American Heart Association states in their Presidential Advisory: 

“Taking into consideration the totality of the scientific evidence, satisfying rigorous criteria for causality, we conclude strongly that lowering intake of saturated fat and replacing it with unsaturated fats, especially polyunsaturated fats, will lower the incidence of CVD.” (3)

So why are some people still averse to consuming seed oils in favor of ingredients like beef tallow that are high in saturated fats?

What the Critics Say

The arguments against seed oils are largely perpetuated by media, podcasters and social media influencers, and mainly fall into three broad categories:

1. Linoleic acid in seed oils allegedly causes inflammation and oxidative stress in the body

2. Seed oil consumption allegedly leads to an imbalance in the optimal intake ratio of omega 6 to omega 3 fatty acids

3. Seed oils allegedly contain toxic byproducts from industrial processing

Let’s unpack these one by one.

Inflammation + Oxidative Stress

Critics claim that the linoleic acid found in seed oils can be converted to another type of polyunsaturated fatty acid called arachidonic acid – which can be converted to other compounds, including some that play a role in inflammation. However, it has been shown that a negligible amount (only about 0.3 - 0.6%) of omega 6 is actually converted to arachidonic acid (5), and multiple scientific studies have found that increased dietary intake of linoleic acid does not have a significant inflammatory effect (6, 7). In fact, arachidonic acid can also be converted to other compounds that fight inflammation (8,9).

Seed oil critics also claim that the unsaturated nature of polyunsaturated fatty acids makes these fatty acids more vulnerable to oxidation –– meaning that oxygen can attach to the carbon backbones of the fatty acids and reduce their quality –– and therefore harmful to human health; this is known as the oxidized linoleic acid hypothesis (10). However, as implied by its name, the oxidized linoleic acid hypothesis is simply that - a hypothesis, and it is not backed by any conclusive scientific evidence. Any oxidation of these fatty acids that would occur in, for example, a bottle of vegetable oil does not translate to oxidative stress in the human body, as demonstrated in several clinical trials (11, 12, 13, 14, 15).   

Omega 6:3 Ratio

Starting in the 1990s, scientists began to point out that the ratio of omega 6 to omega 3 fatty acids consumed in the modern western diet was higher than in previous (pre-industrial) times, and that this rise in omega 6 fatty acid consumption may be playing a role in the rise in chronic diseases (16, 17). The argument points out that the omega 6:omega 3 ratio that human beings historically consumed was between 1:1 and 4:1, while the ratio today has grown to 10:1 or more (17). 

However, the global nutrition and health community has begun moving away from using omega 6:omega 3 ratio as a metric in determining health of a diet because it’s more or less inconsequential (1). For example, even if a higher inflammatory status has been shown in studies to be associated with a high omega 6:omega 3 ratio, this may be due to the lack of omega 3 fatty acids consumed in the diet, rather than the mere presence of omega 6’s in the diet. In fact,  studies have shown exactly this – that omega 3 fatty acid intake may be inversely related to inflammatory status (18). Current consensus among health agencies is that it’s more important to ensure sufficient consumption of each type of fatty acid, rather than the relative amounts (1, 19). 

Industrial Processing

Seed oils are also often lumped into broader misleading claims against “ultraprocessed food,” in which “processed” has been co-opted as a false red flag for lack of healthfulness (for more on that debate, check out our blog here). In the case of seed oils, critics claim that the extraction process to make the oils can leave behind toxic byproducts, such as hexane and other solvents. However, any solvents are removed as part of the broader manufacturing process to ensure that the residual solvent is only present, if at all, in trace levels far below safety standards set by regulatory agencies. 

Conclusion

Despite what a fringe cohort of pseudo-science supporters might want you to believe, several decades of real, consistent scientific research has established a clear consensus: seed oils are not categorically bad for you – and can actually have health benefits. So no, you don’t need to replace your vegetable oil with beef tallow.

References

1. Petersen KS, Maki KC, Calder PC, et al. Perspective on the health effects of unsaturated fatty acids and commonly consumed plant oils high in unsaturated fat. British Journal of Nutrition. 2024;132(8):1039-1050. doi:10.1017/S0007114524002459

2. Hooper L, Martin N, Jimoh OF, Kirk C, Foster E, Abdelhamid AS. Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev. 2020 Aug 21;8(8):CD011737. doi: 10.1002/14651858.CD011737.pub3. PMID: 32827219; PMCID: PMC8092457.

3. Sacks FM, Lichtenstein AH, Wu JHY, Appel LJ, Creager MA, Kris-Etherton PM, Miller M, Rimm EB, Rudel LL, Robinson JG, Stone NJ, Van Horn LV; American Heart Association. Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association. Circulation. 2017 Jul 18;136(3):e1-e23. doi: 10.1161/CIR.0000000000000510. Epub 2017 Jun 15. Erratum in: Circulation. 2017 Sep 5;136(10):e195. doi: 10.1161/CIR.0000000000000529. PMID: 28620111.

4. Mozaffarian D, Micha R, Wallace S. Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS Med. 2010 Mar 23;7(3):e1000252. doi: 10.1371/journal.pmed.1000252. PMID: 20351774; PMCID: PMC2843598.

5. Whelan J, Fritsche K. Linoleic acid. Adv Nutr. 2013 May 1;4(3):311-2. doi: 10.3945/an.113.003772. PMID: 23674797; PMCID: PMC3650500.

6. Su H, Liu R, Chang M, Huang J, Wang X. Dietary linoleic acid intake and blood inflammatory markers: a systematic review and meta-analysis of randomized controlled trials. Food Funct. 2017 Sep 20;8(9):3091-3103. doi: 10.1039/c7fo00433h. PMID: 28752873.

7. Ajabnoor SM, Thorpe G, Abdelhamid A, Hooper L. Long-term effects of increasing omega-3, omega-6 and total polyunsaturated fats on inflammatory bowel disease and markers of inflammation: a systematic review and meta-analysis of randomized controlled trials. Eur J Nutr. 2021 Aug;60(5):2293-2316. doi: 10.1007/s00394-020-02413-y. Epub 2020 Oct 21. PMID: 33084958.

8. Poli A, Agostoni C, Visioli F. Dietary Fatty Acids and Inflammation: Focus on the n-6 Series. Int J Mol Sci. 2023 Feb 26;24(5):4567. doi: 10.3390/ijms24054567. PMID: 36901998; PMCID: PMC10003459.

9. Yali Zhang, Hongjin Chen, Wenxin Zhang, Yan Cai, Peiren Shan, Di Wu, Bing Zhang, Hui Liu, Zia A. Khan, Guang Liang, Arachidonic acid inhibits inflammatory responses by binding to myeloid differentiation factor-2 (MD2) and preventing MD2/toll-like receptor 4 signaling activation, Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, Volume 1866, Issue 5, 2020, 165683, ISSN 0925-4439, https://doi.org/10.1016/j.bbadis.2020.165683.

10. DiNicolantonio JJ, O'Keefe JH. Omega-6 vegetable oils as a driver of coronary heart disease: the oxidized linoleic acid hypothesis. Open Heart. 2018 Sep 26;5(2):e000898. doi: 10.1136/openhrt-2018-000898. PMID: 30364556; PMCID: PMC6196963.

11. Utarwuthipong T, Komindr S, Pakpeankitvatana V, Songchitsomboon S, Thongmuang N. Small dense low-density lipoprotein concentration and oxidative susceptibility changes after consumption of soybean oil, rice bran oil, palm oil and mixed rice bran/palm oil in hypercholesterolaemic women. J Int Med Res. 2009 Jan-Feb;37(1):96-104. doi: 10.1177/147323000903700111. PMID: 19215678.

12. Karupaiah, T., Chuah, KA., Chinna, K. et al. Comparing effects of soybean oil- and palm olein-based mayonnaise consumption on the plasma lipid and lipoprotein profiles in human subjects: a double-blind randomized controlled trial with cross-over design. Lipids Health Dis 15, 131 (2016). https://doi.org/10.1186/s12944-016-0301-9

13. https://pubs.rsc.org/en/content/articlelanding/2022/fo/d1fo03759e 

14. Costa E Silva LM, Pereira de Melo ML, Faro Reis FV, Monteiro MC, Dos Santos SM, Quadros Gomes BA, Meller da Silva LH. Comparison of the Effects of Brazil Nut Oil and Soybean Oil on the Cardiometabolic Parameters of Patients with Metabolic Syndrome: A Randomized Trial. Nutrients. 2019 Dec 23;12(1):46. doi: 10.3390/nu12010046. PMID: 31877968; PMCID: PMC7019763.

15. Vijayakumar M, Vasudevan DM, Sundaram KR, Krishnan S, Vaidyanathan K, Nandakumar S, Chandrasekhar R, Mathew N. A randomized study of coconut oil versus sunflower oil on cardiovascular risk factors in patients with stable coronary heart disease. Indian Heart J. 2016 Jul-Aug;68(4):498-506. doi: 10.1016/j.ihj.2015.10.384. Epub 2016 Jan 13. PMID: 27543472; PMCID: PMC4990731.

16. Lands WE. Impact of daily food choices on health promotion and disease prevention. World Rev Nutr Diet. 2001;88:1-5. doi: 10.1159/000059744. PMID: 11935941.

17. A.P. Simopoulos, Evolutionary aspects of diet, the omega-6/omega-3 ratio and genetic variation: nutritional implications for chronic diseases, Biomedicine & Pharmacotherapy, Volume 60, Issue 9, 2006, Pages 502-507, ISSN 0753-3322, https://doi.org/10.1016/j.biopha.2006.07.080.

18. Fontes JD, Rahman F, Lacey S, Larson MG, Vasan RS, Benjamin EJ, Harris WS, Robins SJ. Red blood cell fatty acids and biomarkers of inflammation: a cross-sectional study in a community-based cohort. Atherosclerosis. 2015 Jun;240(2):431-6. doi: 10.1016/j.atherosclerosis.2015.03.043. Epub 2015 Apr 3. PMID: 25897795; PMCID: PMC4511480.

19. Jackson, K.H., Harris, W.S., Belury, M.A. et al. Beneficial effects of linoleic acid on cardiometabolic health: an update. Lipids Health Dis 23, 296 (2024). https://doi.org/10.1186/s12944-024-02246-2

20. Jackson KH, Harris WS, Belury MA, Kris-Etherton PM, Calder PC. Beneficial effects of linoleic acid on cardiometabolic health: an update. Lipids Health Dis. 2024 Sep 12;23(1):296. doi: 10.1186/s12944-024-02246-2. PMID: 39267068; PMCID: PMC11391774.