The science on fasting as a diabetes treatment seems legitimate (even if early/still evolving), but claiming it cures other "incurable diseases" seems unsupported (particularly if you don't specify WHAT diseases).

Weight loss in general helps combat some other illnesses like high blood pressure, and while fasting might be a means to that end (i.e. weight loss) I've not read studies that looked at if fasting is more beneficial than other forms of weight loss.

Heck, even the fasting diabetes thing is very young science, I wouldn't call even that conclusive yet.