Glossary · Nutrition and probiotics
Prebiotic
In one sentence
A prebiotic is a substrate that is selectively utilised by host microorganisms and confers a health benefit, according to the 2017 consensus definition of the International Scientific Association for Probiotics and Prebiotics (ISAPP).
Also known as: prebiotic fibre · prebiotic substrate
What is a prebiotic?
The term was coined in 1995 and went on to collect more than a dozen definitions. In 2017 an ISAPP expert panel (Gibson et al., Nat Rev Gastroenterol Hepatol) agreed a common one: a substrate that is selectively utilised by host microorganisms conferring a health benefit.
Two words carry the weight. Selectively: being fermentable is not enough; the compound must favour particular groups of microbes rather than the whole microbiota. Benefit: there must be a demonstrated effect on health, not just a change in microbial composition. The panel also widened the concept beyond carbohydrates and beyond the gut, noting that prebiotics may act at other sites, such as the vagina or the skin.
How it works
Prebiotics reach the colon undigested. There they are fermented by bacteria such as Bifidobacterium and some butyrate producers, which generate short-chain fatty acids, lower local pH and can shift the balance between species.
The consensus distinguishes levels of evidence:
- Established: inulin-type fructans (inulin and fructo-oligosaccharides, FOS) and galacto-oligosaccharides (GOS).
- Candidates: other oligosaccharides, resistant starch, polyphenols and certain fatty acids, with data still emerging.
- Human milk oligosaccharides: with a recognised prebiotic role in infants.
Dietary fibre and prebiotics overlap but are not interchangeable: many fibres are not selective or lack proven benefit, and some candidate prebiotics are not fibre at all.
What the evidence says
The best-studied effects are increases in bifidobacteria, improved bowel habit and, with some fructans, better calcium absorption. For metabolic, immune or mood-related outcomes the evidence is less consistent. Responses vary with diet and baseline microbiota. At higher doses, fermentable prebiotics can cause wind and bloating, and they are among the FODMAPs restricted in irritable bowel syndrome.
Example
A paediatric dietitian reviews the label of an infant formula supplemented with GOS and FOS. She notes the ratio and dose used, checks that the formula has been studied in infants of the relevant age, and records stool frequency and tolerance at follow-up rather than assuming a benefit from the ingredient list alone.
Prebiotics in clinical practice
Xenogene does not sell prebiotics. What it can offer is context: a gut microbiota analysis describes microbial composition, and short-chain fatty acid metabolomics measures fermentation products in faeces. Neither result on its own says which prebiotic to use; interpretation and advice belong with the healthcare professional. More information for clinical teams is available on the professionals page.
Frequently asked questions
Is all fibre prebiotic?
No. To be a prebiotic, a compound must be used selectively by particular microbes and have a demonstrated health benefit. Many fibres are fermentable but not selective, or lack proven benefit. They remain worthwhile in the diet even if they do not meet the definition.
Can prebiotics cause wind and bloating?
Yes. Inulin, fructo-oligosaccharides and galacto-oligosaccharides are fermented in the colon and, particularly at higher doses, can cause wind and bloating. They are also FODMAPs, so people with irritable bowel syndrome or sugar malabsorption may tolerate them less well.
Which foods contain prebiotics?
Inulin-type fructans are found in chicory root, artichokes, garlic, onions, leeks and slightly green bananas, while pulses provide galacto-oligosaccharides. Human milk contains oligosaccharides with a recognised prebiotic effect in infants.
Related terms
- Probiotic
A probiotic is a live microorganism that, when administered in adequate amounts, confers a health benefit on the host. This is the FAO/WHO definition, retained by the ISAPP consensus panel in 2014.
- Synbiotic
A synbiotic is a mixture of live microorganisms and substrates selectively utilised by host microorganisms that confers a health benefit on the host, according to the 2020 ISAPP consensus.
- Dietary fibre
Dietary fibre is the group of plant carbohydrates, plus lignin, that the human small intestine cannot digest or absorb. It reaches the colon, where it adds bulk to stools and is partly fermented by the gut microbiota.
- Short-chain fatty acids
Short-chain fatty acids (SCFAs) are fatty acids with one to six carbon atoms produced by colonic bacteria when they ferment fibre and other non-digestible carbohydrates. The main ones are acetate, propionate and butyrate.
- Butyrate
Butyrate is a four-carbon short-chain fatty acid produced by certain colonic bacteria when they ferment fibre. It is the main energy source for colonocytes and contributes to the function of the intestinal barrier.
Educational content for healthcare professionals and the general public. It does not replace assessment by a healthcare professional: ordering and interpreting any test is the responsibility of the requesting clinician.
Updated on