This article was written by Sophie Gastman, associate nutritionist (ANutr), and reviewed by dietitian Maeve Hanan.
Another questionable nutritional claim circulating the internet is that seed oils are toxic and should be avoided at all costs. They have become such pariahs that some call them “the hateful eight” (rapeseed, corn, cottonseed, soybean, sunflower, safflower, grapeseed and rice bran oils). People claim they can cause anything from headaches to heart disease, but are they really that bad for us?
This article will delve into the science behind seed oils and whether they can be safely included in our diet.
What are seed oils?
Seed oils are a term for oils extracted from plants, also called vegetable oils. Oils are normally extracted from the seed through a combination of heating and chemical extraction. They are often found in ultra-processed foods, but they are also commonly used in cooking and baking.
Here are some common examples of seed oils:
- Rapeseed oil
- Soybean oil
- Sunflower oil
- Corn oil
Are they really unhealthy?
As is the case with most nutrition topics, it’s not black and white.
The demonization of seed oils on the Internet is another example of research being misunderstood and out of control.
Omega-6 fatty acids
The main problem that often arises is related to the omega-6 content of seed oils. Omega-6 fatty acids are a type of fat called polyunsaturated fat, which are essential in the diet because our bodies cannot make them ourselves.
Vegetable oils contain fairly high levels of omega-6, particularly one called linoleic acid. This particular fatty acid plays an important role in promoting skin health and maintaining cell membranes. Linoleic acid itself does not trigger inflammation. Instead, it is converted in the body to another fat called arachidonic acid. This fatty acid serves as a building block for various compounds, some of which play a key role in regulating inflammation.
This is where the concern comes in. If seed oils increase the risk of inflammation, and therefore other inflammation-related diseases like cardiovascular disease and cancer, then surely they must be bad for you. We ?
Although this seems like a logical conclusion, science does not support it. First, only a small percentage of linoleic acid is converted to arachidonic acid in the body. A systematic review of linoleic acid consumption in adults found that high linoleic acid intake did not increase arachidonic acid levels in the body (1).
Second, research has yet to show a relationship between omega-6 fatty acid intake and inflammation.
In fact, some studies have even suggested that linoleic acid consumption may be linked to reduced inflammation (1).
Another study found that linoleic acid consumption and arachidonic acid levels did not increase the risk of heart disease, but those who had higher amounts of it in their blood were 7% less likely to get it. develop (2).
What many health gurus on the internet forget to mention is that arachidonic acid is involved in many other beneficial processes in the body, such as wound healing and blood clotting. It’s also important to remember that inflammation is a welcome response to injury and infection.
Finally, much of the research against omega-6 consumption is based on rodent studies. Unsurprisingly, humans don’t respond to linoleic acid in the same way as mice and rats, simply because we’re not rodents.
The Extraction Process
The second concern about seed oils is the extraction process, with skeptics saying that refined oils end up being full of chemicals and trans fats.
Heat is used to extract oil from the seeds, which can create trans fats. However, the heating process is brief and industrially produced oils in the UK and US contain only trace amounts. In fact, there are regulations that limit the amount of trans fat allowed in our food chain.
The only real problem is when seed oils are reheated and reused repeatedly, such as for frying.
This oxidizes the oil, which will lead to a buildup of toxic compounds. However, this primarily affects restaurants rather than the average home cook. Fortunately, regulations are in place to protect consumers from these risks.
When it comes to other chemicals used to extract the oil, only trace amounts remain in the final product and again oil produced in the UK is subject to rigorous quality controls. For example, hexane is used as a solvent in the extraction process, but most of it is effectively removed during processing. Essentially, the regulations and industry practices put in place ensure that the overall quality and safety of seed oils is maintained.
Nutritional Benefits of Seed Oils
In addition to being a neutral and inexpensive oil for cooking, seed oils also have many nutritional benefits. Canola oil, for example, contains omega-6 and omega-3 fatty acids, which are essential for our brain and heart health. Polyunsaturated and monounsaturated fats in seed oils have also been shown to reduce LDL cholesterol and therefore the risk of heart attacks or other cardiovascular problems. (3). A large study from China even found that higher consumption of plant-based cooking oils, such as canola and soybean oil, compared to butter, was associated with lower mortality (4 ).
Vegetable oils are also full of vitamin E, another essential fat-soluble nutrient that the body cannot make itself. In fact, for many populations, vegetable oils are the primary dietary source of vitamin E intake (5). Soybean and canola oils are also rich in vitamin K; a fat-soluble nutrient necessary for blood clotting and wound healing. Just one tablespoon of canola oil contains 10 micrograms of vitamin K (the recommended daily amount is about 1 microgram per kilogram of body weight).
Should we avoid seed oils at all costs?
The short answer is no. Current evidence does not suggest that seed oils are harmful to our health.
Despite what the internet says, it’s important to separate fact from fiction and always approach nutrition with a balanced perspective. Remember, consuming a diverse range of fat sources can provide a wide variety of health benefits, from lowering cholesterol to providing essential vitamins. No source of fat should be avoided entirely. If you would like to learn more about why it is important to consume a range of fats, check out this article titled “Why do we need fats in the diet?” “.
References
- Rett, BS and Whelan, J. (2011) “Increasing dietary linoleic acid does not increase tissue arachidonic acid content in adults consuming Western-style diets: a systematic review”, Nutrition & Metabolism8(1), p. 36. doi:10.1186/1743-7075-8-36.
- Marklund, M. et al. (2019) “Biomarkers of dietary omega-6 fatty acids and incident cardiovascular disease and mortality”, Traffic139(21), p. 2422-2436. doi:10.1161/circulationaha.118.038908.
- Schwingshackl, L. et al. (2018) “Effects of solid oils and fats on blood lipids: a systematic review and network meta-analysis”, Journal of Lipid Research59(9), pp. 1771-1782. doi:10.1194/jlr.p085522.
- Wu, F. et al. (2020) “Plant-based cooking oil consumption is associated with lower total mortality in a nationwide longitudinal cohort study,” Clinical Nutrition39(12), pages 3703–3710. doi:10.1016/j.clnu.2020.03.031.
- Zhang, Y. et al. (2022) “Contribution of tocopherols present in commonly consumed foods to the estimated intake of tocopherols in the Chinese diet”, Nutrition Frontiers9. doi:10.3389/fnut.2022.829091.