Seed oils, usually labelled "vegetable oils" on food packaging, are extracted from corn, rapeseed (canola), soyabean, sunflower and other seeds. They have become a target of Robert F. Kennedy Jr, America's health secretary, and wellness influencers, who call them "toxic". Some American fast-food chains have swapped them for other fats such as beef tallow or avocado oil.
Manufacturers use chemicals such as hexane, a solvent, to extract extra oil from the seeds after pressing. The oil is then filtered and heated to evaporate the hexane and other molecules that can give it strong flavours or make it go rancid. The result is a cheap, longer-lasting product with a neutral taste. For the levels of oil ingested by the typical American, any trace hexane that may remain is "toxicologically insignificant", according to an assessment published in April 2025 by the federal government.
Critics worry chiefly about the oils' content of omega-6 fatty acids, which they claim are pro-inflammatory and cause cancer, heart attacks and obesity. The main omega-6 fat in seed oils is linoleic acid. Linoleic acid can be broken down into both inflammatory and anti-inflammatory compounds in the body. In randomised trials, increasing participants' consumption of linoleic acid had no effect on inflammatory markers. Seed oils are high in healthy polyunsaturated fats; choosing them over saturated fats like butter lowers cholesterol levels and cuts the risk of heart attacks.
A study in Nature Medicine of 100,000 American health professionals found that those following diets high in vegetable oils lived longer, healthier lives than those whose diets were low in vegetable oils. A round-up of cohort studies published in 2022 by the World Health Organisation found that higher intake of omega-6 fats was linked with lower mortality.
Seed oils are healthier, spoon for spoon, than some of the alternatives championed by their critics, including butter, lard and beef tallow. Over-consumption is usually the consequence of a generally unhealthy diet full of fried or ultra-processed foods.
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