Are seed oils (like canola and sunflower) toxic and inflammatory?

Seed oils are largely polyunsaturated fat, mainly the omega-6 fatty acid linoleic acid. Linoleic acid is exactly what gets blamed, yet the human data point the other way. In a pooled analysis of 30 population studies from 13 countries, with more than 68,000 participants, people with higher levels of linoleic acid in blood and tissue had lower risk of cardiovascular disease and lower cardiovascular mortality, not higher. Linoleic acid was measured as a biomarker, which reflects what people actually ate better than a questionnaire does.

The intervention trials agree. A Cochrane review of 19 randomised trials found that more omega-6 in the diet makes little or no difference to all-cause mortality or cardiovascular events, may slightly lower the risk of heart attack, and lowers total cholesterol.

And the inflammation? The worry rests on a mechanism: omega-6 can be converted to arachidonic acid, which can in turn form inflammation-driving signalling molecules. But the step from test tube to human body does not hold. A systematic review of 15 randomised trials in healthy people found no study where added linoleic acid raised the inflammatory markers we measure, such as C-reactive protein, fibrinogen or cytokines. The body's conversion of linoleic acid to arachidonic acid is also small, and does not seem to rise just because you eat more linoleic acid.

The myth survives because it offers a simple villain. If one modern addition to the diet explains weight gain and disease, the fix is just as simple: remove the seed oil. That the oils are industrially made and relatively new to the plate makes them easy to single out, and "natural" feels safer than "refined" even when the body draws no such line. The mechanistic story also sounds convincing to anyone who hasn't seen the human data next to it. Then there is who benefits from the story. A growing carnivore and "ancestral" movement sells tallow, butter and meat as the heroes of the same tale in which seed oil is the villain, and creators earn attention by going against the dietary guidelines. The villain story is simply more shareable than "it mostly comes down to the whole diet."

You don't need to purge canola or sunflower oil from your kitchen. Cooking at home with them is unproblematic, and swapping some saturated fat for them looks protective, if anything. What deserves attention isn't the oil itself but the company it often keeps: seed oils turn up in a lot of ultra-processed food, and it's the whole of that food, not the seed oil, that is the real concern. Judge a meal by what it's made of, not by the fact that it happens to contain seed oil.