The whole idea of the IF is calorie control - you are expected to go low on calories, much lower than your normal intake on your fasting days (under 1,000 calories is expected). In a 24-36 hour fast (dinner to dinner or dinner to breakfast) you are not expected to have any caloric imput for 24 hrs min, and you are not to compensate it once you break a fast. It is after 72 hours of a complete fasting when problems with catabolic state may start appearing (i.e. you start breaking down muscle).

There are hypothesis floating around that complete or ketonic fast in the 16 to 72 hrs window might help burning fat and/or help activate alpha 2 receptors which may lead to freeing up the stubborn fat (with cardio) and yada-yada-yada, but it has as many yes as it has nays. Like all science. Like all science it gotta be tested on oneself.

Going under 1000 calories for a few days is nit going to make things worse. As long as you feed normally and once in a while over-feed (that's going over your calories). That calorie staggering imitates the normal feeding patterns of the past. It actually helps you because your average calories are low, but your hormones (leptin, ghrelin, etc) are not being suppressed into the fat-conserving mode as they would if you continualy maintain the deficit for over a week. Again, that's all mumbo-jumbo needed to be tested on self. But, yes, remember all the posts from people: "OMG, I ate terribly yesterday, but dropped XYZ lbs this week anyhow, WTF?" Those posts are not a testimony to the dietary benefits of eating pizza daily, but more likely the result of people's hormones level going up, sending a signal to the poor starved body that "Hey, we are in the times of plenty, we don't have to hold on to the fat now."

All and all, the healthy way of doing fasting in my view is simply eating when you are hungry and NOT eating when you are not. If you try IF for a few days a week, and continue binging after a couple of weeks of that practice, it is not recommended to continue fasting.

There are three fasting methods that call for short fasts, Fast 5, Lean Gains and Eat Stop Eat. Fast 5 has a free downloaded leaflet on the net if you sign up for the something-something newsletter. Lean gains is a nightmare to explore, and I doubt it works for people who do not train heavy in a dedicated fashion. Finally, Eat Stop Eat will have a few documents on the net. Warrior Diet might as well, and iirc it has a book as well.

There is also a 4 Hour Body method book out by Ferris, who advocates a controlled overfeed once a week with deficit for the rest of the week (with or without the fasting window).

Hope this helps.

I agree, I prefer that approach as well. It is described as "WHEN" approach by Mark here (it is a good article on fasting & it has a bunch of links to more articles on fasting, lol, if you still want to learn more):

http://www.marksdailyapple.com/why-fast-part-six-choosing-a-method/#axzz29klof400