wreckdiver
I am planning on fasting primarily as a cleansing mechanism. If you do a long fast, the caloric deficit alone will cause a significant amount of weight loss. Yes, much of that will be water weight but a significant amount will be fat, toxins, old fecal matter etc.
If you don't have a plan for a change in dietary habits, of course the weight will come back! I see the fast as kind of a transformation. A goodbye to fat, toxins, etc and a hello to a new way of life.
If you have a sound plan for eating and reduction of toxin intake after the fast, and a person sticks to the plan, I think you will be okay. The metabolism will ramp back up and most of the weight will stay off.
My guess is that if one transitions into a healthy eating pattern after the fast, you will likely gain back about 25% of what you lost. At that point, your metabolism will have recovered and imo the rest will be permanent.
Think of your fat as an immune system reaction to toxic material. After the fast, your immune system will be even more efficient. At that point, if you eat the same crap, your body will react even more aggressively and gain fat.
I am struggling to find the best diet for me and have it about 90% figured out. I plan on fasting for an extended time to lose all the crap and then rotate into that diet. The rest is pure discipline imo- easier said than done of course.