From a friend of mine...
The best answer to the question is "not voluntarily".
First, I have always had problems with hypoglycemia(?), which does not lend itself to fasting and the like. If I don't eat,things follow a very predictable pattern: first I become bitchy and cranky (moreso than usual, anyway), and then I get woozy and wobbly, and finally, my blood pressure, which is normally low to begin with, takes a nosedive to the floor and is usually promptly followed by the rest of me.
Second, I quite simply love food too much. I get cravings where I would happily kill someone if it gets me what I'm craving. If I get a craving before I go to bed, it will keep me up all night because I can't stop thinking about it.
Third, as for the "not voluntarily" part of it? Well, I was a sick kid. I'm sure part of that can be blamed on the circumstances of my birth-- emergency c-section, severely jaundiced (think Big Bird yellow), and the only surviving one of a set of twins. There's more that was wrong, but I can't remember it all at the moment. Basically, I was screwed up from the start.
So I caught just about everything that came along, and was allergic to the rest of it. Jr. high was notable for having both Mono and the measles one year apart, and both of those involved "fasting" on my part. With mono, I was so bad that I would debate whether I really needed to get up and go to the bathroom, because it took too much effort-- that's how sick I was. I was out of school for a month and a half, and then only did half days for another month when I finally made it back.
The measles didn't wipe me out as much, but I just couldn't keep food down and had no appetite to begin with. For about a week and a half, I lived on a little bit of fruit juice to keep my blood sugar up, and that was it. This was also the only time in my life I ever successfully lost weight-- in that week and a half, I dropped from Around 160lbs down to just under 125lbs, which really was too thin for me. Thankfully, I got well just as summer (and waterskiiing & swimming season) was starting, so I was able to keep things down around 140, 145, which was just about perfect. I stayed that way until I went to college.
So that's my tale. I've thought of trying fasting again, but there's just no way I could do it and be able to function normally. My body just won't let me do it, betweem nutball food cravings and sugar crashes. And honestly, I'm beginning to believe my Doctor-- my weight isn't going to do anything until I get my stress level down, so I doubt fasting would do any good any way, at least in the long term.