In addition to a healthy diet, taking probiotics regularly can improve mood and decrease anxiety and depression. Stress, antibiotics and a poor diet allow bacteria and yeast to flourish in your gut, destroying the healthy flora that keeps you happy and calm. You can find probiotics in your local health food store. However, you can also take your daily dose of probiotics in the form of fermented foods and beverages. Kimchi, sauerkraut, kefir and beet kvass all provide probiotics naturally.