The microbiome: An actor or stage for the beneficial action of probiotics, prebiotics, synbiotics, and postbiotics?

Probiotics, prebiotics, synbiotics, and postbiotics are required, by definition, to confer a health benefit on the host. It is often presumed the host microbiome plays a central role in the mechanism of action of these substances, collectively referred to here as “biotics.” However, the definitions of both probiotics and postbiotics do not include an associated mechanism nor the involvement of the microbiome. The definitions of prebiotics and synbiotics require evidence of selective utilization by the host microbiome, but do not state that confirmatory evidence must be provided that this utilization causes the associated health benefit. In this perspective, we discuss evidence supporting a role for the microbiome in delivering these health benefits and whether or not measuring microbiome alterations can serve as important readouts of efficacy. We also discuss the possibility of expanding the biotics family with substances such as bacteriophage, fermented foods, and live dietary microbes.