Ultra-refined, highly processed foods are packed with cheap, flavourless seed oils—but how much of the health risks associated with these foods are a result of the seed oils themselves? Healthy seeds like chia and flax get a lot of attention for their nutritional benefits. But what about other seeds that are used for oils?
What is seed oil?
Seed oil is any vegetable oil that comes from the seed of a plant. Sunflower, canola, corn, cottonseed, soybean, grapeseed, safflower, and rice bran are all common seed oils, referred to as “the hateful eight” by some social media wellness influencers.
Olive oil is considered a vegetable oil, because it’s not derived from the seed of the olive. Although avocados and coconuts are botanically classified as fruits, they’re often referred to as vegetable oils. And, while peanut oil is considered a seed oil, it’s also a common allergen.
Omega-3s and omega-6s
All sources of dietary fat are a combination of saturated, monounsaturated, and polyunsaturated fatty acids. Polyunsaturated fats also include omega-3 and omega-6 fatty acids.
Skeptics of seed oils maintain that the omega-6 fatty acids found in seed oils can cause chronic inflammation. This is because linoleic acid, the most common omega-6, is converted into arachidonic acid, which is a building block for compounds that cause inflammation.
However, a 2017 meta-analysis of randomized controlled trials found that increased dietary intake of linoleic acid does not have a significant effect on blood concentrations of inflammatory markers. This is likely because only a small percentage, about 0.2 percent, of omega-6 is converted to arachidonic acid.
What’s more, arachidonic acid is also a precursor for compounds that fight inflammation in the body. Research, such as the 2023 findings in the International Journal of Molecular Sciences, shows a higher intake of omega-6 fatty acids is associated with improved cardiovascular health and better glucose metabolism. The American Heart Association also supports the inclusion of omega-6s as part of a healthy diet to prevent cardiovascular disease.
How is seed oil made?
The process of producing common seed oils often involves crushing the plant material, extracting the remaining oil with organic solvents, and deodorizing the oils to provide a neutral flavour and stability when cooking at high temperatures.
Chemical extraction
Seed oil critics claim the chemical extraction process leaves toxic byproducts, such as hexane, in the oils. While hexane is considered hazardous in gas form and inhalation in high amounts is a concern, when it’s used as a liquid solvent to extract the oil from the seeds, it then evaporates. Canadian regulations set permitted maximum residue levels of hexane in seed oils and other foods.
Mechanical extraction
Another way seed oils can be made is by mechanical extraction through cold pressing or expeller pressing of the plant seeds. There are no chemical solvents in this process, but these oils tend to have lower smoke points for cooking, shorter shelf lives, and are more expensive because they are unrefined.
Unrefined oil
This kind of oil, often called “virgin,” has not undergone refining or further processing outside of filtration and careful mechanical extraction.
Easy seed oil salad dressing
Choose a seed oil and mix 3 Tbsp (45 mL) with 1 Tbsp (15 mL) vinegar (such as balsamic) or lemon juice; 1 Tbsp (15 mL) Dijon mustard; 1 Tbsp (15 mL) honey or brown sugar; 1 minced garlic clove; and salt and pepper, to taste.
What’s good—what’s bad?
Ultra-refined, highly processed, deep-fried foods as well as fast foods and snacks are packed with cheap, flavourless seed oils. Such ultra-processed foods also tend to be high in refined carbohydrates; added sugars, including high-fructose corn syrup; and sodium. They provide little in the way of nutritional benefit.
Replacing highly processed foods with whole foods such as fruits, vegetables, lean proteins, whole grains, legumes, nuts, and seeds is a better way to eat healthily. Seed oils can be part of a healthful diet when used in cooking, such as in stir-frying vegetables, oven-roasting fish, or making salad dressings.
Healthy seed oils
|
Oil |
Uses and benefits |
|
canola |
Great for use in stir-frying or for salad dressings, canola oil is rich in good fats and can help reduce the risk of heart disease, when used instead of saturated fats, by reducing LDL (bad) cholesterol in the blood. Canola oil has just 7 percent saturated fat, the least of the common culinary oils, and no trans fat. Canola oil has the most plant-based omega-3 fat of any common cooking oil; high levels of monounsaturated omega-9 fat (oleic acid); and is a source of omega-6 fat. Look for organic to be sure you’re getting non-GMO canola oil. |
|
sesame |
Sesame oil is often mixed with ground meat for dumplings or wontons; it can also be drizzled over roasted or grilled meats or vegetables and, at low heat, can be used for stir-fries. It has a balanced ratio of omega-3, omega-6, and omega-9 fatty acids, which help reduce the risk of heart disease. |
|
extra-virgin olive |
Excellent for use in roasted vegetables and salad dressings, extra-virgin olive oil is rich in healthy monounsaturated fats and has 10.5 percent polyunsaturated fat, such as omega-6 and omega-3 fatty acids. Its predominant fatty acid is oleic acid, which reduces inflammation and oxidative stress. It is also high in antioxidants, is protective against heart disease, helps prevent strokes, and may reduce diabetes risk. |
|
coconut |
Coconut oil can be used to sauté onions, garlic, fish, shrimp, or chicken breasts. It may have antioxidant properties and may reduce stress resulting from exercise and a chronic cold. High in vitamin E, coconut oil is abundant in saturated fat. Some research has found that medium-chain triglycerides, a component in coconut oil, may help boost levels of good cholesterol. Coconut oil is higher in saturated fat than butter and lard. |
|
avocado |
With a very high smoke point, avocado oil can be used for pan-frying, roasting, barbecuing, and baking. Abundant in oleic acid, a healthy fat, avocado oil is also rich in unsaturated fatty acids, which are linked with better heart health. It’s also high in lutein, an antioxidant that benefits the eyes and enhances the absorption of certain important nutrients. |
This article was originally published in the March 2025 issue of alive magazine.
Alexa Everett
Kamarra Morris
Emilie Richardson-Dupuis