The only thing I know for sure, which I was just told, is that yes, it does destroy good bacteria. You would need to buy a probiotic, which contains many strains of live bacteria. You start taking them after your fast/cleanse is finished. If I'm wrong someone correct me!
I bought "Udo's Choice Adult's Brand Probiotic: 8 adult-specific strains at an appropriate strength, 12 billion viable cells, 60 capsules". So I hope it's a good brand. I've at least heard of it before.
I'm only about 13 hours into my first fast, and I don't feel hungry yet, even though my boyfriend is sitting next to me with a cheese & mushroom omelette. Mmm... omelette.