I think it certainly depends what You mean by fasting and for how long You plan on doing it. I actually plan on doing something along those lines soon but for me it will be either twenty-four or fourty-eight hours of no food and no water. I plan on doing this after about a week of complete isolation.
I do think abrupt changes may affect the body negatively. Hence, I said that it depends how long You plan on fasting and what kind of fasting.
If You plan on staying away from food but You will allow liquids then, I think You would not have many problems. You could have protein shakes or add vitamins to your water ... it all depends ...
If You are going for no food and no water, I encourage You to be careful. Prepare your body by limiting food from before - maybe a month before the day You plan to begin your fasting ... Eating less and less food each day - smaller and smaller portions at longer and longer intervals, will help You adapt.
Do a lot of research and listen to your body - that is perhaps my best tip for You. Other than that, I wish You all the best and may Wakan Tanka guide your path.
In Faith and Love there is Power.