Hello margaux,
there is no real need to replenish your intestinal flora post-fast, as the body is very selective and discerning about its use of reserves and the preservation of essential elements such as good bacteria.
I had no personal need to do so after my own two prolonged fasts of 25 days and then 30 days, and my own digestion was improved enormously thereafter. This has also been the experience of thousands of fasters for the last 150 years.
The need for the replenishment of good bacteria comes only after taking Antibiotics , which no Alternative advocate of health would consider taking anyway.