Beneath that hard-won flat belly, your gut is teeming with trillions of bacteria that help you digest food as well as thwart intruders. You can give these “friendly” bacteria a boost by adding probiotics—the live microorganisms found in yogurt and other fermented foods—to your body.

Over the years, researchers have pinpointed specific bacterial strains that can ease irritable bowel syndrome (IBS) and help prevent and treat vaginal yeast infections. And preliminary research indicates that other strains may help improve vascular health, battle depression, and even ward off cancer.  While probiotics are by no means a magic pill, many experts feel they’re especially useful when your body’s normal bacterial balance is interrupted—which can happen when you’re stressed, ill, traveling, or taking antibiotics.

It’s easier than ever to get your fix these days: Not only is the yogurt industry exploding ($2.27 billion worth of yogurt and kefir, a fermented milk drink, were sold in the U.S. in 2012, according to the Specialty Food Association), but an increasing number of foods fortified with probiotics are being introduced as well.