Yes, there was the Minnesota Coronary Survey which was an RCT on polyunsaturated fats vs saturated fats. It was launched intending to prove the opposite conclusion, but ended up proving that polyunsaturated fats cause significantly higher mortality rates than saturated fats. It's hard to do better than this as a study because it's an RCT that did not rely on self-reported data (it was conducted in hospitals and nursing homes), and it measured a variable that's challenging to fake and relevant to health (death).