VeryGnawty
"I would like to fast for a few days but I hear that fasting slows the metabolic rate"
I do not agree with that assessment. I don't believe there is any scientific evidence to support it.
"If I went on a mono diet of say like oranges for a few weeks will that spike my blood
Sugar levels?"
Possibly.
The thing to watch with fasting is symptoms. If you are in poor health and overweight as well, fasting will probably be very difficult.