One of the best ways to establish and maintain healthy gut bacteria is to eat fermented foods on a regular basis. This is something that we in America rarely do anymore. In fact, the only fermented food that still remains popular in our culture today is yogurt, and often store-bought yogurts are packed with so much sugar and contain so little live bacteria as to be all but useless.
I highly encourage you, for the sake of your health, to start consuming more fermented foods! The recipe below is a great way to do so. If you don't like cabbage, you can also pickle other vegetables using natural fermentation methods. And there are plenty of other fermented foods you can make as well, including yogurt (which is super easy to make at home), kefir, and kombucha tea.
Natural fermentation is not only easy to do at home, but it is also safe, and really fun! And once you develop a taste for fermented foods, you'll probably start to crave them like I do. :-)
Here's how to make a classic naturally fermented sauerkraut - plus a variation for spicy kimchi if you're feeling more adventurous. (Note: This recipe makes approximately 1 quart, but may easily be doubled if desired. The kimchi recipe may make about 1 1/2 quarts due to the additional ingredients. To make a half-gallon, use a larger head of cabbage, and double the salt.)