Prebiotics
What are prebiotics?
The official definition of a prebiotic is a substrate that is selectively utilised by host microorganisms conferring a health benefit.1 Essentially, it acts as an energy source for bacteria in the gut, enabling them to grow and multiply in numbers.
For a substrate to be classified as a prebiotic it must:
(1) Not be digested by the host
(2) Be selectively utilised by live host microorganisms in a manner that sustains, improves or restores host health
(3) Have demonstrated health benefits in the target host from well-controlled studies.
Sources of Prebiotics
Prebiotics can be found naturally in the diet but are also becoming increasingly available in supplement form or as added ingredients in foods. The dietary prebiotics most extensively studied with regards to prebiotic activity are the non-digestible oligosaccharides such as fructo-oligosaccharides (FOS) and galacto-oligosaccharides (GOS), but also inulin, lactulose and resistant starch.2 When looking for prebiotics added within foods or supplements you should be looking for the specific name of the prebiotic (e.g. FOS) rather than the general term ‘prebiotic’.
There is no official dietary recommendation for prebiotics however the International Scientific Association for Probiotics and Prebiotics (ISAPP) suggest trying to consume at least 5g of prebiotics each day.3
Most prebiotics are dietary fibres but not all fibres are prebiotics. The most common forms of fibre that we eat in vegetables and grains don’t satisfy all three criteria previously stated for them to be considered as prebiotics. However, these fibres still play a major role in maintaining our health as well as in the prevention of various non-communicable diseases. Therefore, their consumption should still be encouraged. Click here to get a better understanding of fibre.
Naturally occurring dietary sources of prebiotics include:
- Fruit: bananas
- Vegetables: jerusalem artichokes, chicory, garlic, onion, leek, shallots, asparagus, beetroot, fennel bulb
- Legumes: chickpeas, lentils, kidney beans, baked beans, soya beans
- Nuts: cashews, pistachios
- Wholegrain: barley, rye, wheat, oats
Prebiotics can also be found in mother’s milk in the form of human milk oligosaccharides (HMOs). These HMOs are able to stimulate the growth of bifidobacteria and aid in the development of the infant’s commensal microbiota4.
Did you know... Synbiotics are the combined use of probiotics and prebiotics, that are known to work synergistically. The combination should consist of a prebiotic that specifically supports the survival and growth of the probiotic strain within the product5.
Impact on Health
There is now more research than ever into the possible health and nutritional benefits of consuming or supplementing the diet with prebiotics. These are some of the health benefits that prebiotics may have a role to play in.1,6,7
Healthy digestion
- Improved bowel function mainly through fibre intake and increased faecal bulking. Prebiotics help soften stools to make its passing easier.
Support the body’s natural defences
- Fermentation of prebiotics generates the production of short chain fatty acids (SCFA) which leads to a drop in pH; this is associated inhibition of pathogen growth and colonisation.
Improve calcium absorption
- The reduction in gastrointestinal pH, due to prebiotics and SCFA production, is also associated with increased calcium solubility; interventions have shown that an increase in galacto-oligosaccharides (GOS) results in an increase in calcium absorption which may be mediated by the gut microbiota, specifically bifidobacteria.8
Satiety
- SCFA produced via fermentation of prebiotics have been shown to regulate satiety via several mechanisms. One mechanism is the possible stimulation of the production of hormones such as peptide tyrosine tyrosine (PYY) and glucagon-like peptide-1 (GLP-1) which are released in response to eating and are involved in slowed gastric emptying and insulin release.
Immune modulation
- Although the mechanisms are unclear and the data are limited, randomised controlled trials have shown positive effects of infant formula containing prebiotics on atopic dermatitis and some allergies in early life.9,10
Impact on the Gut Microbiota
Prebiotics are selectively fermented and can increase beneficial microbial growth, specifically promoting the growth of bifidobacteria in the intestinal tract of infants and adults.11 An increase in such beneficial bacteria in response to prebiotic intake can lead to the increased production of SCFA, specifically acetate, propionate and butyrate, and these SCFA have been shown to play a major role in intestinal and immune health.12
However, it is important to note that changes in the microbiota that are observed due to prebiotic consumption appear to be very individualised.13
Prebiotic Health Claims Status
Most prebiotics are sold as ingredients for food or to be used in dietary supplements. However, the potential health benefits of these prebiotic ingredients have not yet been approved by the European Food Safety Authority (EFSA), as they have deemed that the evidence is not conclusive enough. Prebiotics is therefore not a term recognised by EFSA, and thus foods containing these ingredients can only be labelled as dietary fibre with no association to any health benefits.14
References
For more information on prebiotics visit: https://isappscience.org/for-scientists/resources/prebiotics/
1. Gibson et al. (2017) Nature Reviews Gastroenterology & Hepatology 14:491–502.
2. Slavin. (2013) Nutrients 5(4):1417-35.
3. ISAPP (2017) Prebiotics. Available at: http://4cau4jsaler1zglkq3wnmje1-wpengine.netdna-ssl.com/wp-content/uploads/2019/04/Prebiotics_Infographic_rev1029.pdf [accessed 16 Aug 2019].
4. Bode. (2009) Nutrition Reviews 67(S2):S183-S191.
5. Collins & Gibson (1999) American Journal of Clinical Nutrition 69(5):1052S-1057S.
6. Krumbeck et al. (2016) Current Opinion in Gastroenterology 32(2):110-9.
7. Sanders et al. (2019) Nature Reviews Gastroenterology & Hepatology 16:605-616.
8. Whisner et al. (2013) British Journal of Nutrition 110(7):1282-1303.
9. Moro et al. (2006) Archive of Disease in Children 91(10):814-9.
10. Arslanoglu et al. (2012) Journal of Biological Regulators and Homeostatic Agents 26(3):46-59.
11. Ruberfroid et al. (2010) British Journal of Nutrition 104(S2):S1-63.
12. Tan et al. (2014) Advanced Immunology 121:91-119.
13. Davis et al. (2011) PLoS ONE 6(9):e25200.
14. Delcour et al. (2016) Advances in Nutrition 7(1):1-4.