Prebiotics increase beneficial bacteria that are already there. Probiotics don’t, except maybe soil-based organisms like Prescript-Assist. Correct?

Chris Kresser:  Yeah, generally most probiotics have not been shown to quantitatively increase the beneficial bacteria in the gut because they do not contain species that colonize the gut. Probiotic soil-based organisms like Prescript-Assist and transient commensals like MegaSporeBiotic, transient commensals that do live in the gut, those may be a different story, but we don’t really have any data on that, whereas, yes, prebiotics unequivocally have been shown to increase beneficial bacteria that are already there, and in fact, that is part of the definition of what a prebiotic is.