Seed oils were sold as paint for a century before they were sold as food, and they do in you what they do on a window frame. Linseed oil hardens on a fence post in a few days. Chemists call it a drying oil. Soybean oil hardens too. So does sunflower, so does safflower. They were sold to the paint trade before they were sold to the kitchen. Linoleum was invented in 1860 and it is named after linseed oil, because that is what it is, oxidised and pressed into a floor. The oil does not dry by evaporating. It dries by oxygen attacking the double bonds in its fats and welding them into a hard skin. The oil in your chip pan and the oil in your body carry the same double bonds, so the same attack runs there, with aldehydes thrown off as it goes. A painter calls that curing. A biochemist calls it lipid peroxidation. A doctor calls it inflammation and prescribes something for it. Once the oil is in your fat, it stays about two years, drying from the inside, every time it meets oxygen or sunlight. Butter never dried a fence post. Tallow never varnished a boat. Saturated fat has no double bond for oxygen to attack, which is why it sits in the pan for a week and why it sat in your great-grandmother's cells for a lifetime. A fat that sets hard in the air was never a candidate for the inside of an artery. The flooring industry understood the chemistry in 1860. The heart charity recommended it in April.