Man, you really brought this thread back?? Must have been searching through the archives
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The thing that never made sense to me is that if you're eating 2000cal for example and spend (2000 minus X)calories digesting that food, you have X calories left for moving, living, and healing the body.
If you eat nothing, you actually have to break down energy within your body for anything you want to do. So if you fast, you'd have to break down X calories within your body just to be able to go about your daily day, and then after that your body is somehow going to say "hmmm, maybe i should further deplete my evolutionary safety net of fat reserves to repair this bum knee that I 'never had energy to fix' when I had a constant influx of calories"?
People who fast don't have extra energy from not having to digest food, they are often staying at home, resting and avoiding strenuous activities. From everything I read on these forums, your body encourages as little energy expenditure as possible while fasting; to spend extra energy going around curing random ailments doesn't make sense.
I'll propose an alternate, equally kooky idea:
When you're fasting, your body can't fix any of its ailing parts ... no energy. It stops sending pain signals because it doesn't want your body to think that those parts need fixing.