Hi, I don’t know about the insulin, but it might be worth reading the following site https://thebloodsugardiet.com/
This is Michael Mosley’s attempt to address diet in relation to people who are either diabetic or pre-diabetic. I think one of his diet plan options for blood sugar includes fasting so I expect the issue around insulin might be covered somewhere on that site – If it’s not covered in the FAQ then I’d suggest trying the forum section or the search function.
If you want to do a 5:2 program, you might also find it useful to read the 5:2 option on that site as it’s tailored to the needs of people with blood sugar issues.