You don't necessarily need probiotics — a type of "good" bacteria — to be healthy. However, these microorganisms might help with digestion and offer protection from harmful bacteria, just as the existing "good" bacteria in your body already do.

Prebiotics are nondigestible carbohydrates that act as food for probiotics. When probiotics and prebiotics are combined, they interact beneficially (symbiotic relationship). Fermented dairy products, such as yogurt and kefir, are considered synbiotic because they contain live bacteria and the fuel they need to thrive.

Probiotics are in foods such as yogurt and sauerkraut; prebiotics are in whole grains, bananas, onions, garlic, soybeans and artichokes. In addition, probiotics and prebiotics are added to some foods and available as dietary supplements.

Although more research is needed, there's evidence that probiotics might help:

• Treat diarrhea, especially after taking certain antibiotics
• Treat irritable bowel syndrome
• Speed treatment of certain intestinal infections
• Prevent or reduce the severity of colds and flu
• Ease allergic disorders such as eczema and hay fever

Probiotics and prebiotics are also being studied for effectiveness and safety in other diseases, such as diabetes, cancer and heart disease.

Side effects are rare, and most healthy adults can safely add foods that contain prebiotics and probiotics to their diets. If you're considering taking supplements, check with your doctor to be sure they're right for you.

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Sept. 12, 2017 See more Expert Answers