Prebiotics

According to the International Scientific Association for Probiotics and Prebiotics (ISAPP), a prebiotic is defined as a substrate that is selectively utilised by host microorganisms conferring a health benefit. This definition is deliberately broad — encompassing not only fermentable dietary fibres (such as inulin, fructooligosaccharides and galactooligosaccharides) but also non-carbohydrate compounds and applications beyond the gut — and requires evidence of both selective utilisation and a demonstrated health outcome, not merely substrate availability. Well-characterised prebiotics reliably increase populations of Bifidobacterium and Lactobacillus species, enhance SCFA production, and improve stool consistency; effects on harder clinical endpoints such as glycaemic control and immune function have been shown in some trials but are modest and context-dependent. The prebiotic concept should be distinguished from dietary fibre generally: fibre is broadly fermented by many taxa, whereas the selectivity criterion for prebiotics is more stringent and differentiates them from general substrate provision.

Last reviewed: May 1, 2026