There's a BBC Horizons documentary called "Eat, Fast, Live Longer", which is relatively easy to find online, eg on Vimeo. Michael Mosley (a doctor) tried a few fasting options, and in the end recommended one he calls "The Fast Diet" or "The 5:2" diet. The basic premise is by restricting calories to 1/4 of normal twice a week (500 calories for women, 600 for men) your body goes into "repair mode", fixes things (DNA, cancers, etc, in theory), grows new brain cells (because if you're hungry you clearly need to be smarter to find food), and you lose weight. There's more about it here, though there are better forums around. You can get the book he wrote too, it's here on Amazon (with GZ referrer tag), but honestly watching the documentary is enough and the book has nothing really that important in it.
The way I find easiest is to skip both breakfast and lunch on Mondays and Thursdays - busy days at work so you don't really notice, plus I get to work earlier and leave earlier :) While you can eat during the day I find it best to just have dinner - otherwise you're not really fasting, you're just eating small meals. You obviously have to eat good foods, ideally lower in sugar or carbohydrates, meat, veges, legumes, not so much fruit, grains, etc. A great way to track calories you eat and what you burn through exercise is My Fitness Pal.
Because of an upcoming event I'm doing alternate day fasting at the moment, and I'm having no problems with it. The first time you do it you get a bit hungry, and you do get an occasional pang, but all in all I was surprised how easy it was. Gentle exercise on fast days seems important, yesterday I did around 500 calories of exercise and ate 600 calories, so the net energy balance result is I effectively didn't eat yesterday. Since I wasn't eating all the energy has to be taken from fat - muscle doesn't seem to be burned. Your metabolic rate actually goes up slightly when you don't eat, the opposite of what people who say "eat six meals a day" think. You obviously eat less calories, which I think is the main way it works, but I think there's some other effect going on to. If you eat to excess on the eating days you won't lose any weight, obviously.
I was put onto it by a guy at work, who lost quite a bit of weight over six months. My Mum's doing it, and has lost about 4kg in a month. I've lost about 6kg in six weeks, and I wasn't huge to start with - the bigger you are the faster you lose weight. I mentioned it to my doctor, who seemed happy with it, and said most people eat far too much and it's not a bad thing to be a bit hungry sometimes.
Interesting articles. Web MD. Nerd Fitness.
This is meant to be an informational post for people who might need a bit of help in this area. I'm not particularly interested in debates around whether or not it's a good idea, since it was recommended by a doctor and supported by my own doctor. Fasting is done by many cultures.