Prebiotics

A prebiotic is defined by international consensus as a substrate that is selectively used by host microorganisms to confer a health benefit. In everyday terms: food for your resident gut bacteria rather than live bacteria themselves.

It matters because it is the distinction most 'gut health' marketing blurs — probiotics add microbes, prebiotics feed the ones you already have. The best-established prebiotics are specific fibres such as inulin and fructo- and galacto-oligosaccharides, found in foods including onions, garlic, leeks, oats and bananas.

In practice, a varied, fibre-rich diet supplies prebiotic substrates without a supplement; increases are best made gradually, as fermentation can cause wind and bloating at first.

Sources

• Gibson GR, et al. ISAPP consensus statement on the definition and scope of prebiotics. Nat Rev Gastroenterol Hepatol 2017;14(8):491-502; PMID 28611480