I wanted to add another data point to this thread. Today I took a tablespoon of virgin coconut oil about 3 hours before my 20 mile long run. Everything else was held constant from last week: same crappy weather, same amount of sleep, more-or-less the same meal the night before, same wakeup/evac routine and basically the same running route. I normally wake up 3 hours before my alarm goes off to go to the bathroom, so on the last 3 long runs I have used that time to eat a small bowl of plain oatmeal and go back to bed. Last night I just stirred in the tablespoon of coconut oil into the oatmeal.
The first 2/3 of the long run felt basically the same. It was the last 1/3, which included some MP miles, where I noticed that my legs felt a little more solid than they usually did at that point. I was still breathing the same as I usually do but there was a significant difference in comfort level at MP for that last 1/3 of the long run. I realize this is just one data point, but there it is and it's about as controlled for other factors as I could've reasonably done. There's always a possibility that I've made a jump in fitness within the last week but my other runs during the past week would not support that idea, i.e., they felt about the same as the previous week.