The fat burning from fasting actually kicks in a lot sooner than that. Usually within 6 hours if I am not mistaken.
I started fasting for weight loss and for health as a lifestyle just recently. I picked up a book called Eat Stop Eat which has loads of good information backed by research.
The way I fast is 1-2 times per week for 24 hours. I normally start in the afternoon or evening after a meal. Then I fast for 24 hours until that same time the next day when I break the fast.
The important thing is not to go through famine and feasting cycles. Its important to eat as you NORMALLY would when breaking a fast or on the other days of the week. If you over eat you can cancel out any of the fat burning that took place by storing extra calories from overeating.
Longer fasts are certainly effective, but more difficult. They also don't take into account the perspective of weight lifters and strength trainees who need to be constantly refueling their bodies.
For me fasting is a permanent solution to weight loss and weight management. I eat healthy 90% of the time, and have my treats 10% of the time, along with 1-2 24 hour fasts per week.
Some of the major benefits for me have been being freed from calorie counting, weighing my food, constantly cooking/cleaning/eating multiple meals a day, worrying about protein consumption and nutrient macros. All of that is gone now, I just eat healthy whole foods with an occasional fast. It is liberating to say the least.
It's lack of faith that makes people afraid of meeting challenges, and I believed in myself. ~Muhammad Ali
You must have long-range goals to keep you from being frustrated by short-range failures. ~Charles C. Noble
July 6th 2010: 225 lbs, 24% body fat
Nov 30th 2010: 181 lbs, 12% body fat
Dec 28th 2010: 177 lbs, 11% bf
Total weight loss 48 lbs.