Is It Legit?
Debunked
“Seed oils are toxic”
Educational, not medical advice. Always consult a qualified healthcare provider before changing your diet, supplements, or routine. Full disclaimer.
What the science says
Seed oils are not toxic. The polyunsaturated fat they are mostly made of - the soft kind that stays liquid at room temperature, also found in nuts, seeds and fish - has been tested in clinical trials, and swapping it in for saturated fat lowers the risk of heart attacks and strokes rather than raising it.
Linoleic acid, the main omega-6 fat in seed oils, does not increase oxidative stress (cell damage from unstable molecules) at the amounts people normally eat.
The claim mixes up cooking-oil chemistry with the separate, well-documented harms of ultra-processed food.
Full analysis
The seed-oil-is-toxic claim rests on three ideas:
- too much omega-6 fat, one of the two main families of polyunsaturated fat in food
- harmful oxidation when the oil is heated
- inflammation caused by linoleic acid, the main omega-6 fat in seed oils
None of the three holds up against the trial evidence.
A 2017 American Heart Association advisory and a 2020 review by Cochrane, an independent network that pools the results of all the trials on a question, both concluded that replacing saturated fat with polyunsaturated fat (the soft fat that makes up most of a seed oil) lowers the risk of heart attacks and strokes by 17 to 30 percent - the opposite of what the claim predicts.
Heating any cooking oil past its smoke point, the temperature at which it starts to smoke and break down, does create harmful compounds. That applies to many fats, not just seed oils, and it is a different process from how the fat behaves once eaten.
The idea that the ratio of omega-6 to omega-3 fat matters is plausible in theory but untested in human trials, and the Mediterranean diet, which has the strongest evidence for a long life, also contains plenty of omega-6.
The real distinction is between oils used at normal cooking heat and repeatedly reheated industrial frying oil. Ultra-processed foods that happen to contain seed oils are unhealthy for other reasons, not because of the oil itself.
Key studies
The 2 studies that carry the verdict, out of 3 reviewed.
[1]Dietary Fats and Cardiovascular Disease: A Presidential Advisory from the AHA
Sacks FM et al. · Circulation · 2017
A 2017 American Heart Association advisory reviewed the trial evidence and concluded that replacing saturated fat with unsaturated fat, including the polyunsaturated fat in seed oils (the kind that stays liquid at room temperature), lowers the risk of heart attacks and strokes by 17 to 30 percent.
View paper[2]Reduction in saturated fat intake for cardiovascular disease
Hooper L et al. · Cochrane Database of Systematic Reviews · 2020
This review by Cochrane, an independent network that pools the results of trials on a question, found that cutting saturated fat and replacing it with unsaturated fat lowers the risk of heart and circulatory disease, and seed oils are one of the main sources of that unsaturated fat in the diet.
View paper