Probiotics and prebiotics are two parts of food that may support gut health.

Probiotics are specific living microorganisms, most often bacteria or yeast that help the body digest food or help with symptoms of certain illnesses. Probiotics are naturally found in fermented foods such as yogurt and sauerkraut.

Prebiotics are parts of food the body doesn't digest but that may be used by microorganisms. Prebiotics may trigger the growth of the "good" germs in the gut. Prebiotics mainly are in high-fiber foods.

Probiotics and prebiotics also are added to some foods and come in the form of dietary supplements.

When mixed, probiotics and prebiotics are called synbiotics.

Researchers continue to look for a link between gut microorganisms and health conditions. This includes conditions such as allergies, diabetes, obesity, depression, irritable bowel syndrome, and dental cavities and gum disease.

Research has shown promise that probiotics and prebiotics may be helpful. But it hasn't yet proved that probiotics and prebiotics improve health and are safe for everyone.

Side effects from probiotics and prebiotics seem to be rare. Most adults who don't have health concerns can safely add foods that have prebiotics and probiotics to their diets.

But the U.S. Food and Drug Administration doesn't regulate probiotic and prebiotic supplements. There hasn't been much study of their safety. There have been instances of probiotics given to premature infants causing serious or fatal infections.

If you're thinking about taking supplements, check with your healthcare professional to be sure they're right for you.