Table 1.

Definitions and main points about probiotics, prebiotics and synbiotics

Approach	Definition	Main points	References
Probiotic	Live micro-organisms that, when administered in adequate amounts, confer a health benefit on the host	Probiotics must have been shown in well-controlled studies to confer benefits to health	25
		Commensals from human samples, with adequate evidence, can be probiotics
		Live cultures associated with fermented foods but have no evidence of a health benefit are not probiotics
		Undefined faecal transplants are not probiotics
Prebiotic	A substrate that is selectively utilised by host micro-organisms conferring a health benefit	Most prebiotics are given orally and target the gut microbiota although other sites such as the vaginal tract, oral cavity and skin are under investigation	35
		Health benefits include cardiometabolism, mental health and bone
		Currently established prebiotics are carbohydrate-based, but other substances such as polyphenols and PUFA may evolve
		Beneficial effect(s) of a prebiotic on health must be confirmed in the host for its intended use
Synbiotic	A mixture, comprising live micro-organisms and substrate(s) selectively utilised by host micro-organisms, which confers a health benefit on the host	Host micro-organisms include both autochthonous and allochthonous micro-organisms (such as probiotics)	36
		A complementary synbiotic is a mixture of a probiotic plus prebiotic
		A synergistic synbiotic is composed of a live microbe(s) and a selectively utilised substrate(s), but neither needs to meet the minimum criteria stipulated previously for probiotics and prebiotics