In 1968, Ancel Keys & Ivan Frantz began a randomized control trial involving 9000+ people to study the effects of replacing saturated fat with vegetable oils high in linoleic acid.
The study concluded in 1973, but the complete results remained unpublished during Keys' lifetime.
In 2013, the raw data was discovered at the estate of Ivan Frantz.
Analysis of the data showed that while replacing saturated fats with vegetable oils did reduce serum cholesterol by 14% on average, it did not reduce the risk of death from coronary heart disease or other causes.
In fact, cardiovascular mortality increased when saturated fats were replaced. According to the paper, "There was a 22% higher risk of death for each 30 mg/dL (0.78 mmol/L) reduction in serum cholesterol."