Bugs in your belly!
Our intestines have a lot of bugs in them, I've seen it said that we have about 1kg of bacteria living in our innards. That is quite a lot. The balance of bug that we have is important. For example if we take certain antibiotics which kills off the "good" bacteria along with all the "bad" bacteria. The result is a horrible case of diarrhoea.
The treatment for such situations is usually live yoghurt. It is live in that the cultures in the milk were not killed off by pasteurisation (i.e. heat) before consumption. These live bugs help re-cultivate the required bacteria in our guts.
It makes sense to have a regular supply of stuff to keep these bacteria in good balance, they aid effective digestion and health tremendously. Fermented products such as sauerkraut, blue cheeses, kombucha, pickles, yoghurts, soy sauce, pepperoni and other foods are all good sources of fermented foodstuff.
Sorry, but beer and wine doesn't count. That is just yeast, and both the alcohol and yeast will have the opposite of the desired effect. sorry about that.