What is the science behind 5:2?

Since I learned my valuable lesson, I've been thinking about tweaking my 5:2 diet regimen.  My fast days are on Wednesday and Saturday.  (I know!   Saturday you say?   yes.  I get to sleep late, we generally stay in and my kids are often at my mom's so I go to bed early and feel like I'm only fasting for half the time)  However, for the next couple of weeks, I have things to do on my fasting Saturdays as well as I'll be out of town for two separate weeks Wed - Sun which covers both of my fasting days!

What's a girl to do?  Of course this got me to (over)thinking my upcoming dilemma.  What is it exactly about the 5:2?   Is it simply calories in vs calories out?   Is it the act of fasting that is burning the extra fat?   Is it the act of shocking the system?   What makes this WOE work?  

Here is my thinking.  My TDEE is 1427.  So my total caloric intake for the week including my two fast days is 1427 * 5 = 7135 + 400 + 400 = 7935.  Because of my TDEE, my fast days are around 350 but I even up to 400.    So now, let's take the weekly caloric intake of 7935 / 7 which gives me 1133 calories a day.  If I only allow myself 1133 calories a day and do not fast, will I still loose weight?   This would be the calories in vs calories out method of thinking.

With that way of thinking though, I'm not actually fasting, so I'm not sure it would work.  Do I need to do the 1133 calories in the 16:8 window so that my body has time to burn all that extra fat?

I tried to discuss this with my husband, but he believes that it is shocking the system that is working in our favor so he doesn't think much of the calories in / calories out method.

Certainly I do not want to count calories every day for the rest of my life which is why 16:8 doesn't overly appeal to me.  16:8 is your TDEE - 20%.  I could however do it for a couple weeks because of my upcoming Saturdays.  As for my upcoming trips, I'll have to swap my days for Tues and then Mon.  My trips are only a week apart, so this could get tricky but I do not want to worry about what I'm eating while I'm on vacation.

If anyone can make the 5:2 diet complicated, it would be me.