Our digestive tracts house more microbial cells (mostly bacteria) than we have human cells in our entire body. Recent scientific studies have shown that those gut microbes influence our digestive system at both the cellular and molecular levels. Our digestive system, in turn, affects (and is affected by) our overall nervous system function. Thus, it is important to feed those microbes and maintain a gut-microbe-friendly environment.
One way of improving our nutrition is to ferment some of our foods. Sauerkraut, fermented dill pickles, and kim chi are all great fermented foods and easy to try in your own kitchen. The living cultures of microbes breakdown the foods so that our bodies can take up the nutrients more easily. They also help to repopulate our continually turning-over gut flora.
Todd Caldecott has a great post on fermenting your food: http://www.toddcaldecott.com/index.php/food/how-to-cook/136-fermenting
Mark Sisson (Mark’s Daily Apple) has a recipe for fermented dill pickles: http://www.marksdailyapple.com/naturally-fermented-dill-pickles/#axzz1qLA580OT
Sandor Katz dedicates his life to lacto-fermented foods: http://wildfermentation.com/