My understanding is that the body can go a long time without food but cannot go more than a few days without water. The body can even produce it's own sugars (via liver and pancreas) to keep itself running for a little while.
Without food, the body will metabolize body fat, then muscle, then organs, which leads to organ failure and death (or a life with likely complications of damaged organs). It seems like a very difficult and uncertain way to ctb, as it would take a long time and force feeding could be imposed.