What are Prebiotics?

Kerry Beeson BSc (Nut. Med.) Nutritional Therapist

Prebiotics are a source of food for probiotics to grow, multiply and survive in the gut. Because they are fibres they cannot be absorbed or broken down by the body, enabling them to nourish friendly bacteria, particularly the Bifidobacteria genus, this helps to support our microbiome and overall gut health. You can read more on The microbiome, all you need to know. 

Prebiotics in food

Prebiotics occur naturally in our diet, and prebiotic fibres can be found in jerusalem artichokes, garlic, chicory, and onions amongst other things. One may have to eat large quantities of these foods to have a ‘bifidogenic’ effect – that is, to increase the levels of friendly bacteria in our intestines. For this reason, many people find it easier to take a prebiotic supplement, or a combination of probiotics and prebiotics (called a synbiotic) to ensure they are feeding their resident friendly bacteria. A good example of this type of supplement is OptiBac 'For every day', which contains a combination of well researched probiotic strains and FOS fibres. 

Research shows that there are different types of prebiotics, just as there are different types of friendly bacteria. With prebiotics, the key differentiating factor is the length of the chemical chain – short-chain, medium-chain or long-chain. This determines where in the gastrointestinal tract the prebiotic has its effect, and how the benefits may be felt by the host.

Common prebiotics include inulin, Fructooligosaccharides (FOS; probably the most researched of the prebiotic fibres), galactooligosaccharides (GOS), lactulose and lafinose. An expert panel convened by the International Scientific Association in 2017 agreed on the following definition: 'A prebiotic is a substrate that is selectively utilised by host microorganisms conferring a health benefit'1

For more information on prebiotics, healthcare professionals can read the in-depth article and research analysis by Dr Aisling Dwyer, 'The Uses of Prebiotics'.

NB: In some cases, prebiotics can cause minor disturbance/flatulence in the first few days of taking them… but after a few days of continued use (once the intestines have adapted to the prebiotics), this discomfort tends to disappear.

For more information about this, see our FAQ page: Are there any side effects from taking live cultures?


Gibson G et al., "Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics," Nature Reviews Gastroenterology & Hepatology , vol. 14, p. 491–502, 2017.