Just to follow up: I felt great by Wednesday evening and I ran again this morning. My body felt great and I really felt like I had cleaned myself out, which was the original goal. I had a biggish dinner last night (Large Chicken kebab with extra salad) and some porridge this morning, before heading out for another run. I really went 100% with the run, pushing myself on a very hilly course: several steep inclines that I went all out on. I was supposed to run 3 miles, but mistakenly ran 3.5, which is better, of course, than running less than I should have (3.5 mi 25:47 436 kCal 7:22 min/mi). I wasn't too happy with the porridge though: had me feeling very heavy initially and I think I will run on an emptier stomach on Saturday when I go nine miles.
The verdict on the fast was very positive and I'll go at it again on Monday, I think. It really helps the next day's eating too: you would think you'd gorge, but you don't. You feel... peaceful. I like that. This next time, though, I think I might add some kilo-calories to the mix, maybe a shake in the morning and in the evening. Try to get the empty feeling without any of the negative bits.
On to the next one..