Why it’s important: “The microbiome—the blend of good and bad bugs that live in our gut—is an exciting area of research,” explains Alex Kemper, M.D., professor of pediatrics at Nationwide Children’s Hospital, in Columbus, Ohio, and deputy editor of Pediatrics. Probiotics contain microorganisms that are the same as or similar to the beneficial bacteria in our intestines that crowd out illness-causing bacteria, and they can also reduce inflammation. (Breastfed infants may have different gut populations from formula-fed babies, which could be why they didn’t benefit equally in this review.)