Seed Oils: The Internet's Most Argued-About Cooking Fat Finally Goes On Trial
One corner of the internet says seed oils are slowly killing you. The other says they're perfectly fine. Both sides are louder than the evidence. Let's read the evidence.
Few topics in modern nutrition have generated more heat and less light than seed oils. On one side you have a coalition of carnivore diet influencers, ancestral health advocates, and people who are very emotionally attached to beef tallow, insisting that canola oil, sunflower oil, and their relatives are an industrial poison responsible for virtually every modern chronic disease.
On the other side you have mainstream nutrition bodies largely treating seed oils as a neutral or positive swap for saturated fat, backed by decades of cardiovascular research.
Both sides are louder than the evidence warrants. Let's read the evidence.
The Case For The Prosecution
The core concern about seed oils centres on their high omega-6 polyunsaturated fat content — specifically linoleic acid — and the argument that modern diets have dramatically increased the omega-6 to omega-3 ratio compared to what humans historically consumed. Omega-6 fatty acids can be converted in the body to arachidonic acid, a precursor to pro-inflammatory compounds.
The secondary concern involves the oils' instability under high heat — polyunsaturated fats oxidise more readily than saturated or monounsaturated fats when heated, potentially producing aldehydes and other compounds that have shown harmful effects in cell studies.
The Case For The Defence
Large-scale observational studies and clinical trials repeatedly find that replacing saturated fat with polyunsaturated fat — including from seed oils — is associated with reduced cardiovascular risk. The Mediterranean diet, which has some of the strongest longevity evidence in nutritional epidemiology, uses olive oil predominantly but is not low in polyunsaturated fats overall.
The linoleic acid to inflammation link, while mechanistically plausible, has not consistently translated into higher inflammatory markers in well-designed human trials. The body appears to regulate arachidonic acid conversion fairly tightly regardless of linoleic acid intake within normal dietary ranges.
The seed oil debate has become a proxy war for deeper disagreements about industrial food, ancestral eating, and who you trust — and that noise is drowning out a much more boring and useful answer.
The Verdict
The catastrophic harm narrative is not supported by the weight of current evidence. But the concern about dietary fat diversity and omega-6 to omega-3 balance is legitimate and worth taking seriously without catastrophising.
Eating a diet dominated by heavily refined seed oils in ultra-processed foods is a reasonable thing to reduce — not because the oil is a poison but because that dietary pattern as a whole is associated with poor health outcomes. Cooking occasionally with sunflower oil is not a crisis. Eating predominantly whole foods cooked in a variety of fats, including olive oil, is a sensible approach regardless of where you land on the seed oil debate.
Diversify Your Fat Sources, Don't Panic About Any One Of Them
Use olive oil most of the time. Keep butter for flavour. Use seed oils occasionally without catastrophising. Vary your fat sources the same way you vary your vegetables — range beats obsession every time.
