First, let’s establish what can happen to flow-mediated dilation after a meal. Some people seem to think that no change is a good goal, though I don’t agree. In this article, a clear difference is show: a high-carb, high-fiber meal causes FMD to increase, while a low-carb, high-fat meal causes it to decrease. So no change in FMD is better than it decreasing, but it can increase after certain types of meals.
So, what do oils in general do to FMD? They lower it! This study shows either olive oil, soybean oil, or palm oil all lower FMD whether fresh or deep fried. What about butter? It lowers it. What about coconut oil? It lowers it.
Now, sometimes olive oil can be found to have a neutral effect, such as the study above I cited. Or even when olive oil is combined with red wine it can possibly increase FMD, but that appears to be due to the wine. But in general, refined oils appear to lower FMD with occasional exceptions.
On to part 3…