While some bacteria can cause illness, our bodies are full of “good” bacteria that benefit us, too. (About five pounds of it, according to some estimates!) It's long been known that people who eat more fermented and cultured foods that contain beneficial bacteriatend to live longer and experience fewer intestinal issues throughout their lives. The best easily available food source of good bacteria is live-culture yogurt.

Recently, scientists have also discovered that your gut bacteria can communicate with your brain along the “gut-brain axis,” and that changing the body’s bacterial balance can alter brain activity, especially as it relates to mood—sometimes for the better. The details aren’t clear yet, but the first hints are here. For example, one study on women found that taking a fermented milk product with five specific bacteria changed the activity in brain regions that control emotion and sensation. Other studies have shown that changing gut bacteria has the potential to reduce anxiety and sadness.