Certain people can't fast, like diabetics, for obvious reasons. There are certain people that have to eat regularly or their body goes into a complete tailspin. In your case you may have a weakness that makes it difficult as well.
For most people fasting is not only something they can do but should do. It's a chance for the body to rest and catch up on the removal of waste and bad tissue. If you go from a situation of excess to moderation, as you propose, it will still take a long time for the body to catch up. Perhaps that period of careful moderation will put your body in a position to fast, whereupon it can further speed healing.
Fasting is a very natural way of healing. Our ancestors had to endure it as a matter of survival, so dealing with this is programmed into our genetics. Our bodies know what to do and go about it in a very logical way.
It's just like if someone has an allergy to iodine. First, address the allergy (which I understand can be done), then begin to take Iodine for its benefits. Build up your system so it's in a position to fast, then fast.