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Probiotics and prebiotics

Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find one of our health articles more useful.

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What are probiotics?

Probiotics are defined as "live micro-organisms that confer a health benefit on the host when administered in adequate amounts." The major source of probiotics for humans is dairy-based foods containing intestinal species of Lactobacillus or Bifidobacterium. The most common type used is Lactobacillus acidophilus (also known as one of the "friendly bacteria"), a species of Gram-positive, rod-shaped bacteria often found in the intestinal tract of humans and animals, the human mouth and vagina. It is an anaerobic organism that produces lactic acid which reduces the pH. This may have an inhibitory effect on other organisms, especially candida. The yeast Saccharomyces cerevisiae and some Escherichia coli and Bacillus species are also used as probiotics.

What are prebiotics?

Prebiotics are defined scientifically as "selectively fermented ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health." They are non-digestible carbohydrates (mainly oligosaccharides and non-starch polysaccharides) which act by promoting the growth and/or activity of probiotic bacteria in the gut. The most common are fructo-oligosaccharides (FOS), inulin and galacto-oligosaccharides. They are found in various vegetables and fruit such as tomatoes, onions, garlic, leeks, asparagus and bananas. Prebiotics are relatively stable and, unlike probiotics, can be relied on to arrive relatively unchanged in the gut despite the presence of digestive enzymes.

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What are synbiotics?

Synbiotics contain prebiotics and probiotics in the same preparation.

Possible uses of probiotics

Many commercially available products (eg, yoghurt) are classed as foodstuffs. This means that they escape the rigorous testing for efficacy which is applied to medicines. They have biologically plausible modes of potential action as displacers of pathogens, immunomodulators or local antimicrobial agent secretors. Initial scientific investigation indicates some evidence of usefulness of probiotics in some areas and a definite impetus to continue research into their effects. Doses and recommendations/guidelines for their routine use, however, have yet to be established, pending ongoing research findings. Most benefit has been demonstrated, naturally, for gastrointestinal disorders.

Gastrointestinal disorders

  • Prophylaxis of antibiotic-associated diarrhoea. Studies vary, and ongoing research into the dose of probiotics continues, but there is evidence that probiotics may prevent some antibiotic-associated diarrhoea. 1 2

  • Prevention of traveller's diarrhoea. 3

  • Prevention of Clostridium difficile diarrhoea. There is evidence of moderate certainty that probiotics are safe and effective in preventing C. difficile diarrhoea.4 Public Health England guidelines on C. difficile management, however, do not yet recommend their routine use 5

  • There has been interest in the use of probiotics to induce remission in inflammatory bowel disease and to treat pouchitis, but there is very little evidence for their benefit for these indications. 6 7 8

  • Irritable bowel syndrome (IBS). There is some evidence that probiotics may improve symptoms of IBS, although ongoing studies are needed to identify which patients benefit, and optimal regimens. 9 10 The National Institute for Health and Care Excellence (NICE) recommends that if patients wish to try probiotics they should take them at a dose recommended by the manufacturer for a minimum of four weeks. 11 The more recent BSG guidelines suggest that they might be tried for up to 12 weeks, but agree with NICE that it is not possible to recommend a specific type of probiotic. 12

  • Eradication of Helicobacter pylori. A meta-analysis concluded that fermented milk-based probiotic preparations increased eradication rates in patients on standard eradication therapy by 5-15%.13 14

  • Necrotising enterocolitis. There is only low to moderate certainty for the benefits of probiotic therapy for treating this condition in premature babies. 15

Other possible uses

Many studies are ongoing into the possible benefits of probiotics in areas including:

There is some evidence that probiotics can affect immune response, and therefore could have potential benefit in any number of clinical scenarios.25 26

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Possible uses of prebiotics and synbiotics 10

There is much interest in the potential for use of prebiotics and synbiotics. Research is being undertaken to look at possible benefit for an enormous number of areas, including:

  • Immune response. There is some evidence that prebiotics in combination with probiotics may boost the immune response.27

  • Obesity.28 29

  • Type 2 diabetes mellitus.30


Evidence suggests probiotics are safe in the vast majority. However, there is a small risk of adverse effects, such as sepsis. It is therefore recommended that use of these agents be avoided in those who are immunocompromised, severely debilitated, critically ill or postoperative, as this population is most at risk.31 There are differences between probiotic/prebiotic agents and regimens both within clinical trials and the way they are used, and these are not likely to be equivalent. Therefore, there is much work to be done before specific clinical guidelines and recommendations can be made.

Meanwhile probiotics and prebiotics exist in everyday food products on supermarket shelves, as well as in capsules, powders and sachets, from a bewildering array of sources. As doctors, we are not yet in a position to give specific evidence-based advice on exactly which product patients should take in which situation.

Future research

There is no doubt that prebiotics and probiotics are an interesting group that warrants further investigation. Guidelines were produced in 2010 to guide ongoing research.32 Studies on one strain of micro-organism cannot be assumed to apply to others, and experimental studies have often not been extended to humans. Many brands of commercially produced probiotics and prebiotics exist, which are not standardised, and there is concern about the applicability of meta-analyses which extend to such heterogeneous groups of subjects, conditions and treatments. The reader should note that this is a fast developing area and new research is published regularly.

Further reading and references

  • Kellow NJ, Coughlan MT, Reid CM; Metabolic benefits of dietary prebiotics in human subjects: a systematic review of randomised controlled trials. Br J Nutr. 2014 Apr;111(7):1147-61. doi: 10.1017/S0007114513003607. Epub 2013 Nov 13.
  1. Blaabjerg S, Artzi DM, Aabenhus R; Probiotics for the Prevention of Antibiotic-Associated Diarrhea in Outpatients-A Systematic Review and Meta-Analysis. Antibiotics (Basel). 2017 Oct 12;6(4):21. doi: 10.3390/antibiotics6040021.
  2. Goodman C, Keating G, Georgousopoulou E, et al; Probiotics for the prevention of antibiotic-associated diarrhoea: a systematic review and meta-analysis. BMJ Open. 2021 Aug 12;11(8):e043054. doi: 10.1136/bmjopen-2020-043054.
  3. Bae JM; Prophylactic efficacy of probiotics on travelers' diarrhea: an adaptive meta-analysis of randomized controlled trials. Epidemiol Health. 2018;40:e2018043. doi: 10.4178/epih.e2018043. Epub 2018 Aug 29.
  4. Goldenberg JZ, Yap C, Lytvyn L, et al; Probiotics for the prevention of Clostridium difficile-associated diarrhea in adults and children. Cochrane Database Syst Rev. 2017 Dec 19;12(12):CD006095. doi: 10.1002/14651858.CD006095.pub4.
  5. Clostridioides difficile: guidance, data and analysis; Public Health England
  6. Nguyen N, Zhang B, Holubar SD, et al; Treatment and prevention of pouchitis after ileal pouch-anal anastomosis for chronic ulcerative colitis. Cochrane Database Syst Rev. 2019 Nov 30;11(11):CD001176. doi: 10.1002/14651858.CD001176.pub5.
  7. Limketkai BN, Akobeng AK, Gordon M, et al; Probiotics for induction of remission in Crohn's disease. Cochrane Database Syst Rev. 2020 Jul 17;7(7):CD006634. doi: 10.1002/14651858.CD006634.pub3.
  8. Kaur L, Gordon M, Baines PA, et al; Probiotics for induction of remission in ulcerative colitis. Cochrane Database Syst Rev. 2020 Mar 4;3(3):CD005573. doi: 10.1002/14651858.CD005573.pub3.
  9. Cash BD; Emerging Role of Probiotics and Antimicrobials in the Management of Irritable Bowel Syndrome. Curr Med Res Opin. 2014 Mar 26.
  10. Probiotics and Prebiotics - Global Guidelines; World Gastroenterology Organisation, February 2023
  11. Irritable bowel syndrome in adults: diagnosis and management of irritable bowel syndrome in primary care; NICE Clinical Guideline (February 2008, updated April 2017)
  12. Vasant DH, Paine PA, Black CJ, et al; British Society of Gastroenterology guidelines on the management of irritable bowel syndrome. Gut. 2021 Jul;70(7):1214-1240. doi: 10.1136/gutjnl-2021-324598. Epub 2021 Apr 26.
  13. Sachdeva A, Nagpal J; Effect of fermented milk-based probiotic preparations on Helicobacter pylori Eur J Gastroenterol Hepatol. 2009 Jan;21(1):45-53.
  14. Homan M, Orel R; Are probiotics useful in Helicobacter pylori eradication? World J Gastroenterol. 2015 Oct 7;21(37):10644-53. doi: 10.3748/wjg.v21.i37.10644.
  15. Sharif S, Meader N, Oddie SJ, et al; Probiotics to prevent necrotising enterocolitis in very preterm or very low birth weight infants. Cochrane Database Syst Rev. 2023 Jul 26;7(7):CD005496. doi: 10.1002/14651858.CD005496.pub6.
  16. Akelma AZ, Biten AA; Probiotics and infantile atopic eczema. Pediatric Health Med Ther. 2015 Sep 28;6:147-151. doi: 10.2147/PHMT.S50476. eCollection 2015.
  17. Yang G, Liu ZQ, Yang PC; Treatment of Allergic Rhinitis with Probiotics: An Alternative Approach. N Am J Med Sci. 2013 Aug;5(8):465-468.
  18. Iftikhar H, Awan MO, Awan MS, et al; Role of Probiotics in Patients with Allergic Rhinitis: A Systematic Review of Systematic Reviews. Int Arch Otorhinolaryngol. 2022 Jun 17;26(4):e744-e752. doi: 10.1055/s-0042-1749370. eCollection 2022 Oct.
  19. Cardona D, Roman P, Canadas F, et al; The Effect of Multiprobiotics on Memory and Attention in Fibromyalgia: A Pilot Randomized Controlled Trial. Int J Environ Res Public Health. 2021 Mar 29;18(7):3543. doi: 10.3390/ijerph18073543.
  20. Roman P, Carrillo-Trabalon F, Sanchez-Labraca N, et al; Are probiotic treatments useful on fibromyalgia syndrome or chronic fatigue syndrome patients? A systematic review. Benef Microbes. 2018 Jun 15;9(4):603-611. doi: 10.3920/BM2017.0125. Epub 2018 Apr 26.
  21. Huang Y, Wang X, Zhang L, et al; Effect of Probiotics Therapy on Nonalcoholic Fatty Liver Disease. Comput Math Methods Med. 2022 May 30;2022:7888076. doi: 10.1155/2022/7888076. eCollection 2022.
  22. Musazadeh V, Roshanravan N, Dehghan P, et al; Effect of Probiotics on Liver Enzymes in Patients With Non-alcoholic Fatty Liver Disease: An Umbrella of Systematic Review and Meta-Analysis. Front Nutr. 2022 May 23;9:844242. doi: 10.3389/fnut.2022.844242. eCollection 2022.
  23. Maslennikov R, Ivashkin V, Efremova I, et al; Probiotics in hepatology: An update. World J Hepatol. 2021 Sep 27;13(9):1154-1166. doi: 10.4254/wjh.v13.i9.1154.
  24. Ahmadian F, Razmpoosh E, Ejtahed HS, et al; Effects of probiotic supplementation on major cardiovascular-related parameters in patients with type-2 diabetes mellitus: a secondary-data analysis of a randomized double-blind controlled trial. Diabetol Metab Syndr. 2022 Apr 13;14(1):52. doi: 10.1186/s13098-022-00822-z.
  25. Yan F, Polk DB; Probiotics and immune health. Curr Opin Gastroenterol. 2011 Oct;27(6):496-501. doi: 10.1097/MOG.0b013e32834baa4d.
  26. Mazziotta C, Tognon M, Martini F, et al; Probiotics Mechanism of Action on Immune Cells and Beneficial Effects on Human Health. Cells. 2023 Jan 2;12(1):184. doi: 10.3390/cells12010184.
  27. Shokryazdan P, Faseleh Jahromi M, Navidshad B, et al; Effects of prebiotics on immune system and cytokine expression. Med Microbiol Immunol. 2017 Feb;206(1):1-9. doi: 10.1007/s00430-016-0481-y. Epub 2016 Oct 4.
  28. Wang Y, Salonen A, Jian C; Can prebiotics help tackle the childhood obesity epidemic? Front Endocrinol (Lausanne). 2023 May 26;14:1178155. doi: 10.3389/fendo.2023.1178155. eCollection 2023.
  29. Aoun A, Darwish F, Hamod N; The Influence of the Gut Microbiome on Obesity in Adults and the Role of Probiotics, Prebiotics, and Synbiotics for Weight Loss. Prev Nutr Food Sci. 2020 Jun 30;25(2):113-123. doi: 10.3746/pnf.2020.25.2.113.
  30. Kellow NJ, Coughlan MT, Reid CM; Metabolic benefits of dietary prebiotics in human subjects: a systematic review of randomised controlled trials. Br J Nutr. 2014 Apr;111(7):1147-61. doi: 10.1017/S0007114513003607. Epub 2013 Nov 13.
  31. Didari T, Solki S, Mozaffari S, et al; A systematic review of the safety of probiotics. Expert Opin Drug Saf. 2014 Feb;13(2):227-39. doi: 10.1517/14740338.2014.872627. Epub 2014 Jan 3.
  32. Rijkers GT, Bengmark S, Enck P, et al; Guidance for Substantiating the Evidence for Beneficial Effects of Probiotics: J Nutr. 2010 Feb 3.

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The information on this page is written and peer reviewed by qualified clinicians.

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