There could be a whole new continent of health improvements achievable by managing the body's bacterial ecosystem in the way a professional gardener manages a botanical garden.

Is eating an effective way to do that? In the world's cultures there's a wide variety of pro-biotic fermented foods. Do these exist merely because people like the taste? Surely they partly exist as a coping strategy for rotten food, but is that all? I doubt it. In some cultures they're eaten regularly. Let's list some:

• yogurt / cheese / cottage cheese / sour cream / kefir / etc.
• sauerkraut / kim chee / pickled vegetables
• fermented tofu (e.g. stinky tofu)
• fermented rice
• kombucha

Diet generally can dramatically affect which bacteria thrive in the gut (e.g. I recall evidence about sugar consumption, but can't find it). [I don't list bread or wine because as far as I know the agents are mostly dead before we eat them. For that matter, I'm not sure how much is alive in commercially available cheese.][Hygiene practices vary substantially too which probably has an important effect.]