Table 2.

Evidence required for synbiotics using doses delivered in product

Composition	Dosea	Microbiological evidence from trial in target host	Study design	Evidence of health benefit required from trial in target host
Complementary synbiotic
Prebiotic	Sufficient to result in the selective utilization by resident microbiota and a health benefit in the absence of the co-administered probiotic	No additional evidence needed beyond that for the prebiotic component	Two-arm trial of complementary synbiotic and an inert control	Complementary synbiotic is superior to controlb
Probiotic	Sufficient to result in a health benefit in the absence of the co-administered prebiotic	No effect on resident microbiota required	Two-arm trial of complementary synbiotic and an inert control	Complementary synbiotic is superior to controlb
Synergistic synbiotic
Substrate selectively utilized by the co-administered live microorganism	Sufficient to result in the selective utilization by the co-administered microorganism	Evidence that the substrate is selectively utilized by the co-administered live microorganism	Trial of live microorganism(s), selectively utilized substrate(s), combination of microorganism(s) plus substrate(s), and control	Combined effect of synergistic synbiotic is better than the estimated effects of each component separately
Live microorganism that selectively utilizes the co-administered substrate	Sufficient to selectively utilize the co-administered substrate and result in a health benefit	Evidence that the substrate is selectively utilized by the co-administered live microorganism	Trial of live microorganism(s), selectively utilized substrate(s), combination of microorganism(s) plus substrate(s), and control	Combined effect of synergistic synbiotic is better than the estimated effects of each component separately

The unmodified term ‘synbiotic’ can be used on a commercial product label as long as the criteria for either a complementary or synergistic synbiotic are met. There is no restriction on the type of health target but it must be realistic and mechanistically driven. See Table 1 for a list of diseases and conditions targeted to date in human trials of putative synbiotics. Microbial, metabolic and health end points (or suitable biomarkers) must be tracked in the same study for a synergistic synbiotic, in the target host. It is not indicated here, but documentation of the safety of the final blended product for the intended use is required. ^aEffective doses delivered in a commercial product must be present through the end of shelf-life. ^bStudies documenting health benefits conferred by probiotic and prebiotic components are also required.