The seed oil story — how industrialised fat became a health crisis
For decades, seed oils were positioned as heart-healthy alternatives to saturated fat. The chemistry told a different story.
science
Linoleic acid — the dominant fatty acid in sunflower, grapeseed, corn, and soybean oils — is highly unstable under heat. When heated for cooking, it oxidises and forms aldehydes, particularly 4-hydroxynonenal (4-HNE), which are directly toxic to mitochondria, damage DNA, and accelerate atherosclerosis. This was known in the research literature. It was not communicated publicly.
The vegetable oil industry — beginning with Procter & Gamble's Crisco — funded research, influenced dietary guidelines, and successfully repositioned industrially processed polyunsaturated fats as alternatives to saturated fat following Ancel Keys' selective epidemiological work in the 1950s. The result was a public health message built on flawed methodology and significant commercial interest.
The timeline of cardiovascular disease prevalence maps almost exactly onto seed oil consumption increases across the 20th century. The mechanism is understood. The epidemiology is consistent. The conflict of interest in the exonerating research is extensively documented.
Grapeseed oil: 69–78% linoleic acid — the highest of any common cooking oil, a wine industry byproduct repositioned as premium
Sunflower oil: 48–74% linoleic acid — culturally embedded in many European countries as the default cooking fat
Sesame oil: best used cold or as a finishing oil — its lignans offer some oxidative protection but not under high heat
Walnut oil: never heat it — valuable as a cold dressing oil for its ALA content
Stable cooking fats: extra virgin olive oil, coconut oil, butter and ghee from grass-fed animals, beef tallow, duck fat