The first thing to factor in is medication. Gliclazide, insulin or other bg lowering meds would make me be wary. But Insulin dependent T2s fast for hours while doing basal testing, so it isn't of itself, always an issue, but they need to know what they are doing and adjust medication accordingly.
After that, what about any other medical conditions? Both @nosher and I have reactive hypoglycaemia, and we both fast. But because of differences in the way our RH works, i think he water-fasts, while I fat-fast.
Then there is the weight issue. Fasting to lose weight means you wouldn't eat extra between fasts. Fasting and avoiding weight loss means you would.
And the fasting food choices, i mean, why fast part of the time and then eat rubbish the rest of the time? So careful choices needed there.
I'm rather a believer in the idea that the body should (if fed properly*) find its own healthy weight - which doesn't necessarily correspond with BMI tables, or what we want to see in the mirror.
* by 'fed properly' i mean fed below its personal carb-tolerance-level, whatever that may be, and running below its personal-fat-threshold, while getting all necessary nutrients without eating processed foods. But since that healthy weight is, for obese lil' ol' me, a pipe dream at the moment, i accept that its a very personal view of mine that no one else may share.