Glossary · Nutrition and probiotics
Dietary fibre
In one sentence
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.
Also known as: dietary fiber · soluble fibre · insoluble fibre · soluble fiber · insoluble fiber · fibra dietética
What is dietary fibre?
In its 2010 opinion on dietary reference values for carbohydrates and fibre, EFSA defines dietary fibre as non-digestible carbohydrates plus lignin. In 2009 the Codex Alimentarius adopted a definition based on carbohydrate polymers of ten or more monomeric units that are not hydrolysed in the small intestine, leaving each country to decide whether to include those with three to nine units.
It covers very different compounds: cellulose, hemicelluloses, pectins, beta-glucans, inulin and fructo-oligosaccharides, resistant starch and gums. Sources include pulses, wholegrains, vegetables, fruit, nuts and seeds.
How it works in the gut
Fibre is usually grouped by its properties:
- Soluble and viscous: forms gels, slows gastric emptying and glucose absorption, and can lower LDL cholesterol.
- Insoluble: increases stool bulk and frequency.
- Fermentable: feeds the colonic microbiota, which turns it into short-chain fatty acids such as acetate, propionate and butyrate.
Some fermentable fibres also meet the criteria for a prebiotic (inulin, for example), but not all fibre is prebiotic.
What the evidence says
In 2010 EFSA set an adequate intake of 25 g a day for adults, based on normal bowel function. Beyond transit, a WHO-commissioned series of systematic reviews and meta-analyses (Reynolds et al., The Lancet, 2019) linked higher fibre intake with lower all-cause mortality and lower incidence of coronary heart disease, stroke, type 2 diabetes and colorectal cancer, rating the certainty of evidence for fibre as moderate. Most of the data are observational: they show association, not proof of cause for any individual.
Individual responses vary. The same fibre can yield different amounts of SCFAs depending on a person’s microbiota, and in conditions such as IBS some highly fermentable fibres can worsen symptoms.
Example
In a clinical nutrition clinic, a food diary shows a fibre intake of around 12 g a day. The faecal SCFA profile requested by the doctor shows low butyrate. The dietitian plans a gradual increase in pulses, oats and vegetables and considers repeating the test a few months later to see whether fermentative activity has changed.
Dietary fibre at Xenogene
Xenogene does not measure the fibre in your diet but its effect: functional metabolomics uses GC-MS to quantify the SCFAs the microbiota produces when it ferments fibre. Its listed uses include monitoring response to a dietary intervention with fibre or prebiotics. Interpretation rests with the professional who requests the test.
Frequently asked questions
How much fibre should I eat a day?
EFSA considers 25 g a day adequate for normal bowel function in adults, and many Europeans eat less. If you increase it, do so gradually and with enough fluid; in some digestive conditions the amount should be adjusted by a healthcare professional.
What is the difference between soluble and insoluble fibre?
Soluble fibre (oat beta-glucans, pectins, gums) forms gels and tends to be more fermentable in the colon. Insoluble fibre (cellulose, lignin in bran) ferments less and mainly adds bulk to stools. Most plant foods contain both.
Why does fibre make me bloated?
Bacterial fermentation of fibre produces gases such as hydrogen and carbon dioxide alongside short-chain fatty acids. Increasing fibre slowly usually helps; if symptoms are severe or persistent, it is worth seeking advice.
Related terms
- 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.
- Prebiotic
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).
- 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.
- Microbiota
The microbiota is the community of living microorganisms (bacteria, archaea, fungi, protozoa) that inhabits a specific site of the body, such as the gut, mouth, skin or vagina.
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.
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