From The Western Way of Death, Malcolm Carruthers, p20-21, 1974 (back when I worked for the East Midland Electricity Board as a COBOL programmer. Boy, were they glad when I left to go to vet school!) Carruthers:
Even when heart attacks started to become a fashionable way of death at and increasingly early age, progress towards discovering their causes still lagged. This was partly because scientific theories naturally tend to be partly based on what has been most recently observed and can be most easily measured. Cholesterol was the ideal choice of culprit as it had been found on the scene of the crime by microscopists. Its footprints in the shape of characteristic clefts could be clearly seen in the walls of some of the affected arteries, where it could be stained a spectacular and guilt-ridden red colour. The chemists were also happy to testify to cholesterol being the "bad egg". There was plenty of it to measure, both in the blood and in the food, and the levels of the two and heart disease tended to bear a suspicious, albeit inconstant relationship. Being nice and stable both in and out of the body, and not one of those will-o'-the-wisp compounds whose blood levels vary wildly during the day and disappear as soon as you think you've got them trapped in a test tube, it was a sitting duck for the collection of chemically incriminating evidence. From here it was a brief exercise in ad hoc reasoning to the "It's what you eat that does it" school of thought that holds sway to this day. This originally suggested that a high cholesterol diet raises blood cholesterol to a level where it is gradually deposited in the walls of the blood vessels and builds up to cause atheroma. For various reasons, this theory was later broadened to include saturated animal fat among the dietary "baddies" in the dock along with cholesterol. Unsaturated vegetable fats, especially the polyunsaturated ones, were cast in the role of "goodies" who were able to combat the evil effects of the "baddies" [note, this was written well before the StarWars movies were released, prescient hey? No mention of The Force though]. The market soon became saturated with unsaturated food products. This was good for the circulation of grocery products and magazines with complicated diet sheets, but appeared to have little effect on the coronary circulation. Heart attack rates obstinately continued to rise.