The basic science is that insulin will cause the BG to drop, and food will make it rise. The trick is making them work together while they work against each other.
In theory (theory because I don't think any of us shoots without feeding, at least not on purpose), you would expect to see a drop in BG more quickly if there's no food on board. And a greater drop as long as no food is given, then a rise once it is given.
It will just make your cycles different, and not as predictable, because the timing of the insulin action won't be "typical".
I think you are using Lantus, right? Might be a good question to post in the TR forum. Maybe ask if anyone has experience with shooting and not feeding right then, so you can look at their spreadsheets to see what their curves look like?
How are you doing Hosanna?
Carl