What’s the Deal with Seed Oils?

You may have seen social media posts blaming “seed oils” for everything from inflammation and “toxicity” to heart disease, diabetes, and even cancer. Some influencers call them “the new poison,” warning that they’re full of “inflammatory omega-6” fats, or that frying with them produces dangerous aldehydes. Here are the common claims we’ve heard in our practice:

● Inflammation & Disease: Seed oils are high in omega-6 linoleic acid, which allegedly converts to pro-inflammatory compounds and raises the risk of chronic disease.

●  Heart & Cancer: Some say seed oils drive obesity, diabetes, heart disease, and even cancer.

● Cooking Concerns: Heating seed oils is said to create toxic oxidation products that damage your body.

Sound scary? Let’s unpack each concern with what science actually shows; no fear-mongering, just clear facts so you can make informed choices.

Seed oils are plant-based cooking oils extracted from the seed of a crop (unlike olive or avocado oil, which are from the fruit). Common examples include canola (rapeseed), corn, soybean, sunflower, safflower, cottonseed, rice bran, and grapeseed oil; often dubbed by influencers the “hateful eight.” Oils are generally categorized as saturated fats, trans fats, or unsaturated fats, and the difference comes down to how hydrogen atoms are bonded within the fat molecule.

These chemical differences affect how the fats behave:

●       Saturated fats (like coconut oil and butter) are solid at room temperature.
●       Unsaturated fats (like olive or canola oil) are typically liquid at room temperature due to their “bent” structure.
●       Trans fats behave similarly to saturated fats and are also usually solid at room temperature. They're found in some meat products and many highly processed or packaged foods.

In reality, seed oils are rich in unsaturated fats. All fats (saturated, monounsaturated, polyunsaturated) are part of a normal diet and help your body absorb vitamins A, D, E, and K. Interestingly, Health Canada actually encourages swapping some saturated fats (like butter, lard, coconut oil) for unsaturated plant oils to improve cholesterol levels [1]. Let’s explore these guidelines and separate the facts from the myths.

Many people hear “high omega-6” and worry that seed oils cause inflammation. Seed oils are indeed high in linoleic acid (an omega-6). Our bodies can convert linoleic acid to arachidonic acid, which in turn can form some pro-inflammatory molecules. But here’s the catch: research shows this doesn’t translate into more inflammation in people. For example, a recent meta-analysis of controlled trials found that eating more linoleic acid did not raise blood inflammatory markers (CRP, IL-6, TNFα, etc.) [2]. Only a tiny fraction of omega-6 is converted to arachidonic acid, and our bodies also make anti-inflammatory compounds from it. In fact, newer reviews highlight the benefits of linoleic acid, including lower risk of heart disease, stroke, and diabetes [3]. For example, a landmark study of 68,000 people in 13 countries found that those with higher blood levels of linoleic acid had a lower risk of heart attack and stroke compared to those with low levels [2].

The bottom line: eating seed oils in moderation does not cause inflammation; if anything, plenty of evidence shows linoleic acid may be net anti-inflammatory [3][4].

What about cancer? Fortunately, no good evidence links eating seed oils to cancer. The World Cancer Research Fund reviewed the science on dietary fats and cancer and found no link between moderate seed oil intake and cancer risk [5]. Importantly, context matters. Seed oils often show up in ultra-processed (fries, chips, etc.), which are linked to disease. In fact, ultra-processed foods are causally linked to obesity, diabetes and cancer risk; this is almost certainly not due to the often tiny doses of seed oils in the products [3]. Rather, it’s likely the excess salt, sugar and refined carbohydrates in those foods doing the damage.

Any oil (seed or otherwise) can indeed break down if you crank the heat past its smoke point or reuse it for hours of frying. Overheated fats can form aldehydes and other compounds that aren’t healthy. But this isn’t unique to seed oils; olive, avocado, coconut, and even animal fats can produce similar breakdown products if burned. In general, refined seed oils have a high smoke point (around 230°C for sunflower, canola, etc.), making them pretty stable for home cooking. For normal cooking methods (such as simmering vegetables, roasting fish, or shallow-frying foods), they hold up well. To minimize any risk, simply avoid smoking the oil (if it smokes visibly, turn down the heat) and don’t reuse the same oil indefinitely.

Importantly, no study has shown that using seed oils in ordinary cooking measurably harms people. One recent study did find that deep-frying oils can generate toxic aldehydes, especially when reused [6]. Home cooks don’t generally reuse oil for dozens of fries like restaurants do. So while good technique matters (like not overheating or keeping oil fresh), there’s no evidence you need to fear seed oils in typical home use.

So where does this leave us? Seed oils are broadly safe to use, and cutting them out entirely isn’t necessary for a healthy diet. They can fit into a balanced pattern just like olive or nut oils. It really comes down to how you use them. Personally, I reach for olive oil most of the time, but because of its lower smoke point, it is not my go-to for high-heat cooking. For East Asian-inspired stir-fries or searing a steak, I use canola oil instead. If you are worried about omega-6s, the smarter move is not cutting out canola oil altogether. It is adding more omega-3s, like salmon, sardines, or flaxseeds, to your plate.

Reference:

[1] Health Canada. (n.d.). Choose foods with healthy fats. Government of Canada. Retrieved September 10, 2025, from https://food-guide.canada.ca/en/healthy-eating-recommendations/make-it-a-habit-to-eat-vegetables-fruit-whole-grains-and-protein-foods/choosing-foods-with-healthy-fats/

[2] Johnson, G. H., & Fritsche, K. (2012). Dietary linoleic acid and inflammatory markers in the blood: A systematic review and meta-analysis of randomized controlled trials. Journal of the Academy of Nutrition and Dietetics, 112(7), 1029–1041. https://doi.org/10.1016/j.jand.2012.03.029

[3] Johns Hopkins Bloomberg School of Public Health. (2023, March 9). The evidence behind seed oils’ health effects. Retrieved September 10, 2025, from https://publichealth.jhu.edu/2023/the-evidence-behind-seed-oils-health-effects

[4] Innes, J. K., & Calder, P. C. (2018). Omega-6 fatty acids: Helpful or harmful? Prostaglandins, Leukotrienes and Essential Fatty Acids, 132, 15–21. https://doi.org/10.1016/j.plefa.2018.03.003

[5] World Cancer Research Fund. (2025, May 20). Are seed oils good or bad for our health? Retrieved September 10, 2025, from https://www.wcrf.org/about-us/news-and-blogs/are-seed-oils-good-or-bad-for-our-health/

[6] Yuan, Y., Wang, X., Han, J., Jiang, Y., & Wang, J. (2023). Analysis of the generation of harmful aldehydes in edible oils during sunlight exposure and deep-frying using high-field proton nuclear magnetic resonance spectroscopy. Food Chemistry, 424, 136393. https://doi.org/10.1016/j.foodchem.2023.136393/