well, this may be worth trying. I found when I got past a distance with a faster speed, I started to burn body fat. I use a running watch with GPS which provides a fairly accurate number of calories and percentage of fat burned. My BGs seemed to do their own thing until I upped my protein intake. I needed the extra protein for muscle repair and noticed that it helped me to level out.
Another thing that has helped me, is to create a running basal rate that reduces the basal rate while I do my long runs, but adds what I took off for 2 hours back starting the hour after I stop running. So, for me, I normally have 1.05 units per hour in the morning. When I run, my run program lowers my basal to 0.05 per hour for two hours. One hour after I stop my run, my basal adds the 1.0 unit I took off for two hours so that I have 2.05 units for two hours then return to my usual basal rate.
It has worked for me. I can start my run in the 5.5 to 6.5 range (sorry, I’m Canadian and don’t know the equivalent) and actually finish with almost the same reading. I do take gel mixed in water during the run, which seems to help keep the energy and BG level.
Hope you find the answer that works for you. I’m sure more will share what works for them.