Is There a Difference Between Observational and Clinical Studies?

In observational trials, a number of them show actually a slight health benefit to those who eat more vegetable oils. The observationis the worst, the clinical studies the best, and the mechanism explains what we see in the clinical study, or or it doesn't. i don't think epidemiology should be used in nutrition. I think it should only be used for true disease s i not just nutrition or not nutrition.