I drink about 500ml of water 2 hours before if I am running over 6k , no special fuelling just yet , that’s the next phase, to work out what I need that won’t adversely affect BG long term.
All of my runs have been first thing in the morning before breakfast. Yesterday fasting BG was 5.5, still fasting post run was 6.4, so a rise of 0.9. I think the largest BG rise I’ve seen was 2.0.