They beneficial enzymes are killed by the bottling or concentration process. Secondly, both grape and apple juice are extremely high in Sugar
content. Restricting one's diet to those two juices would put one on a fast track to blood Sugar
Read the lables -- grape and apple have over 30mg of Sugar
in a 180mg serving. V8 Juice has 11mg sugar in a 340 mg serving.
For the best results on a juice fast, get another juicer and juice veggies, not only fruits. I'll bet there are used juicers on EBay or in the thrift shops. Lots of people buy them with good intensions but don't use them...