Seed oils are toxic. They cause chronic inflammation. They’re driving the obesity epidemic. One prominent voice in American health politics recently called them “worse than glyphosate, herbicides, and pesticides combined.”
In response, fast food chains have switched their fryers to beef tallow. Major food companies are reformulating products. People across North America are throwing out their canola oil and replacing it with butter and lard.
Here’s the question worth asking: is any of this based on actual evidence?
What Seed Oils Are and Why They’re Controversial
Seed oils are cooking oils pressed from plant seeds — canola, sunflower, corn, soybean, safflower, rice bran, grapeseed, and cottonseed. Critics have called these the “Hateful Eight.” They’re distinct from oils pressed from fruit, like olive oil or avocado oil, though the nutritional distinction is less dramatic than the branding suggests.
In Canada, canola oil has particular roots — it was developed in the 1970s at the University of Manitoba, and the name literally stands for Canadian oil, low acid. It’s been a staple of Canadian cooking and agriculture ever since.
The anti-seed-oil argument goes like this: seed oils are high in omega-6 polyunsaturated fats, particularly linoleic acid. Linoleic acid can theoretically convert in the body to arachidonic acid. Arachidonic acid has been linked to inflammation. Therefore, seed oils cause inflammation. Therefore, seed oils are making us sick.
It’s a chain of logic that sounds plausible. But each link has a significant problem — and the actual human research tells a consistently different story.
What the Science Actually Says
The evidence on seed oils is substantial, and it runs contrary to what the anti-seed-oil movement claims.
A 2019 study measured linoleic acid levels in the blood and tissue of over 68,000 participants across 30 studies in 13 countries, following people for up to 30 years. People with the highest levels of linoleic acid in their blood had a lower risk of cardiovascular disease — with especially strong associations for cardiovascular mortality and stroke.
A 2025 study presented at the American Society for Nutrition’s annual meeting analyzed blood markers from nearly 1,900 people using objective biomarkers rather than diet surveys. Higher linoleic acid in blood plasma was associated with lower inflammation markers, lower insulin resistance, and better cardiometabolic health overall.
A separate 2025 study published in the journal Nutrients examined almost 3,000 people and found no connection between linoleic acid levels and inflammation markers whatsoever.
And a 2026 peer-reviewed paper in Nutrition Today concluded after reviewing the full body of clinical trial evidence: linoleic acid does not promote inflammation or oxidative stress.
The specific mechanism critics rely on — that linoleic acid converts to inflammatory arachidonic acid — doesn’t hold up under scrutiny either. Only about 0.2% of dietary linoleic acid actually converts to arachidonic acid. And arachidonic acid itself produces both pro- and anti-inflammatory signalling molecules. As Penn State’s lead researcher on the topic put it: “Linoleic acid is incorrectly claimed to cause inflammation. It is now well established that linoleic acid intake has a negligible impact on blood or tissue levels of arachidonic acid.”
The scientific consensus — from Johns Hopkins, Memorial Sloan Kettering, and multiple independent peer-reviewed reviews — is consistent: seed oils do not cause inflammation. In large human studies, they’re associated with better cardiovascular outcomes, not worse.
What’s Actually Worth Worrying About
Here’s where the anti-seed-oil movement deserves partial credit: they’ve correctly identified a real problem. They’ve just pointed at the wrong cause.
Ultraprocessed foods — chips, fast food, packaged snacks, sugary drinks — are genuinely associated with poorer health outcomes. Seed oils are often used as ingredients in those foods. But those foods are problematic because they’re engineered to be hyper-palatable, nutritionally empty, and easy to overeat. The oil is not the problem. The chips are the problem.
The one legitimate concern in this space: the ratio of omega-6 to omega-3 fats in the modern diet is higher than it was historically, and some research suggests this imbalance may matter for inflammation over the long term. But the solution to that isn’t removing seed oils. It’s adding more omega-3s — from fatty fish, flaxseed, or fish oil supplements.
A separate minor concern: cooking any oil at very high heat repeatedly, as in a commercial deep fryer running all day, can degrade the oil and produce oxidation products. This is a real but specific concern — and it’s a very different claim from “canola oil in your stir fry is toxic.”
Three Things to Do Based on the Actual Evidence
1. Don’t throw out your cooking oil. Canola, sunflower, and other seed oils are safe, backed by decades of human research, and associated in most large studies with better health outcomes than the saturated fat alternatives being recommended as replacements.
2. Focus on ultraprocessed food, not the oil. If you want to reduce your risk of chronic disease, the real target is food engineered in a factory — long ingredient lists, minimal nutritional value, engineered flavour. That’s where the evidence points. The oil is not the story.
3. Add omega-3s rather than subtracting seed oils. Concerned about your omega-6 to omega-3 ratio? The answer is more fatty fish, more flaxseed, or a quality fish oil supplement — not avoiding canola oil. Solve the actual problem rather than a manufactured one.
The Bottom Line
The fear around seed oils is real, loud, and politically driven. The science, however, is fairly clear: seed oils do not cause inflammation. In large human studies conducted across decades, the primary fat in seed oils is consistently linked to better cardiovascular outcomes, not worse.
The real concern is ultraprocessed food. And the oil is not what makes those foods harmful.
Don’t let a well-marketed panic pull your attention away from what actually matters.
Ready to cut through the noise and build a plan based on what the research actually supports? Book your free No-Sweat Intro at Catalyst.
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Coach Chris Cooper is the owner of Catalyst Fitness in Sault Ste. Marie, Ontario. The Catalyst podcast releases new episodes weekly at catalystgym.com/blog.
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