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What are probiotics, prebiotics and synbiotics?

Probiotics, prebiotics, and synbiotics are functional food components that can alter the gut microbiota.

Probiotics are composed of live, beneficial bacteria1 found in foods such as yogurt, kefir, and kombucha, as well as supplements. Probiotics can enrich your gut microbiota in many ways, including producing vitamins and other useful compounds (such propionate or butyrate), maintaining healthy gut barrier function, helping maintain a balanced immune response, and helping fight off harmful bacteria.

Prebiotics are supportive dietary components – such as inulin and other fibers – that selectively feed beneficial gut bacteria, which can have a positive effect on the microbiota,2 similar to taking probiotics.

Finally, synbiotics are a combination of probiotics and prebiotics, which can have a better effect together than pro- or prebiotics can have on their own.3

The value of consuming probiotics, prebiotics, and synbiotics has been recognized by current gastroenterology guidelines and standards (e.g. the World Gastroenterology Organization, 2017).4

What are the common effects?

Probiotics and prebiotics are widely accepted to help a broad range of health conditions and symptoms. Though many claims have been made by the producers of pre- and probiotic supplements, not all of these have been backed by scientific studies. However, research increasingly shows that some supplements can be beneficial for certain conditions. Scientists have found, for example, that consuming probiotics and prebiotics can:

  • Decrease the risk of type 2 diabetes by decreasing blood glucose and insulin levels,5,6,7 as well as improving metabolic control in subjects with diabetes.8,9
  • Decrease blood lipid levels.10
  • Increase immune activity to help the efficacy of the influenza vaccine.11
  • Improve symptoms of irritable bowel syndrome and supplement standard therapy.12,13
  • May help prevent Clostridium difficile-associated diarrhea,14,15 as well as diarrhea caused by taking antibiotics16 or related to travel.17
  • Reduce the number of patients experiencing acute upper respiratory tract infections (URTIs), reduce the number of episodes of URTIs, and decrease the need for antibiotics in treating URTIs.18
  • Improve symptoms and quality of life for ulcerative colitis patients.19
  • Help to decrease blood pressure in people with high blood pressure.20,21
  • Decrease constipation.22
  • Reduce risk of depression.23
  • Help to relieve small intestinal bacterial overgrowth symptoms.24

What are the mechanisms of action?

  • Probiotics and prebiotics can modify gut microbiome composition and activity.25,26
  • Probiotics can inhibit gut pathogen growth or function by direct (producing antimicrobial compounds or changing the pH) or indirect (contributing to immune balance or gut barrier integrity) mechanisms.27
  • Probiotics can alter mood by influencing the biosynthesis of compounds that can enter the blood and affect organs outside the gut.28
  • Prebiotics are selectively degraded by the microbiota, producing short-chain fatty acids (SCFAs). Butyrate, one type of SCFA, is known to have immunomodulatory effects, protect the gut barrier, and have an apoptotic (potentially anticarcinogenic) effect.30 Some prebiotics can induce the growth of butyrate producers in the gut microbiota.29
Related to apoptosis, a mechanism of controlled and programmed cell death involved in an organism’s growth or development.

How does this relate to my microbiome?

Several studies show that the use of pro-, pre-, and synbiotics can help to improve symptoms of different health conditions (see above) by changing microbiota composition and activity. Dietary fiber is a favorite food for many beneficial gut bacteria, including those that produce molecules such as butyrate, which reduces inflammation. You can talk to your doctor about whether adding pre- or probiotics to your diet might be right for you.

Which diseases/topics are related to probiotics, prebiotics and synbiotics?

Other encyclopedia entries related to probiotics, prebiotics, and synbiotics include:

How can people take action?

There are several ways to increase the intake of prebiotics, probiotics, or synbiotics.

The main prebiotic fibers are inulin-type fructans (including inulin, fructo-oligosaccharides and oligofructose), galacto-oligosaccharides, xylo-oligosaccharides, arabinoxylan-oligosaccharides, and resistant starches. To increase your intake of prebiotics, you can add more fruits, vegetables, beans, nuts, and seeds to your diet.31,32,33,34,35 Important sources of prebiotics include:

  • Fruits: apples, bananas, peaches, watermelon, oranges, and pears
  • Vegetables: artichokes, chicory root, Jerusalem artichokes, onions, shallots, asparagus, dandelion greens, garlic, leeks, lettuce, acorn squash, bitter gourds, corn
  • Wholegrain cereals: rye, wheat, barley, oats
  • Legumes: lentils, chickpeas, peas, beans
  • Seeds: almonds, flaxseed, sesame

Probiotics are found in certain foods – such as yogurt, kefir, kimchi, and kombucha – and in dietary supplements. There are even probiotic-containing products that are not food items, such as skin products.

Some of the more well-studied probiotic microorganisms are:

  • Lactobacillus rhamnosus GG (known as Lactobacillus GG)
  • Lactobacillus delbrueckii (including Lactobacillus bulgaricus)
  • Lactobacillus casei
  • Bifidobacterium animalis
  • Bifidobacterium longum
  • Bifidobacterium bifidum
  • Lactobacillus reuteri
  • Lactobacillus acidophilus
  • Lactobacillus brevis
  • Lactobacillus fermentum
  • Lactobacillus helveticus
  • Streptococcus thermophilus
  • Escherichia coli strain Nissle 1917
  • Akkermansia muciniphila
  • Saccharomyces boulardii

Examples of food items that can contain probiotics are:

  • Fermented foods, including some types of yogurt, fermented milks, kefir, kimchi, natto, and others.36,37
  • Probiotic supplements, which usually come in the form of a pill that contains dried bacteria which revive when ingested. Lactobacillus and Bifidobacterium species are currently the most popular probiotic supplements. Such supplements are available in supermarkets, drug stores, and stores selling general dietary supplements.

Synbiotics are usually available as commercial supplements. Consult with your healthcare provider about which option is best for you.

When you take probiotics, prebiotics, and/or synbiotics, consider the following:

  • The effectiveness of probiotics, prebiotics, and synbiotics depends on the condition being treated and the strain – or compound of strains – ingested. Some strains or food types might work better for one person than for another. For example, if one type of Lactobacillus has been shown to help prevent diarrhea after taking antibiotics, another Lactobacillus strain might not have the same effect.
  • Consuming more than the recommended dosage of probiotics, prebiotics, or synbiotics may lead to side effects such as excessive flatulence, abdominal noises (rumbling or gurgling), diarrhea, abdominal pain, or bloating.38,39,40 If you are not used to taking probiotics, it might also be a good idea to start with a low dose in the first week, and slowly increase the dose towards the recommended amount.

Please consult your healthcare provider about the recommended use of probiotics, prebiotics, and synbiotics for different health conditions.


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2. Gibson, G. R., Probert, H. M., Loo, J. Van, Rastall, R. A., & Roberfroid, M. B. (2004). Dietary modulation of the human colonic microbiota: updating the concept of prebiotics. Nutrition Research Reviews, 17(2), 259–275.

3. Schrezenmeir, J., & de Vrese, M. (2001). Probiotics, prebiotics, and synbiotics—approaching a definition. The American Journal of Clinical Nutrition, 73(2), 361s–364s.

4. World Gastroenterology Organisation Global Guidelines (2017). Probiotics and prebiotics.

5. Kellow, N. J., Coughlan, M. T., & Reid, C. M. (2014). Metabolic benefits of dietary prebiotics in human subjects: a systematic review of randomised controlled trials. British Journal of Nutrition, 111(7), 1147–1161.

6. Ruan, Y., Sun, J., He, J., Chen, F., Chen, R., & Chen, H. (2015). Effect of Probiotics on Glycemic Control: A Systematic Review and Meta-Analysis of Randomized, Controlled Trials. PLOS ONE, 10(7), e0132121.

7. Sun, J., & Buys, N. J. (2016). Glucose- and glycaemic factor-lowering effects of probiotics on diabetes: a meta-analysis of randomised placebo-controlled trials. British Journal of Nutrition, 115(7), 1167–1177.

8. Kasińska, M. A., & Drzewoski, J. (2015). Effectiveness of probiotics in type 2 diabetes: a meta-analysis. Polskie Archiwum Medycyny Wewnetrznej, 125(11), 803–813.

9. Li, C., Li, X., Han, H., Cui, H., Peng, M., Wang, G., & Wang, Z. (2016). Effect of probiotics on metabolic profiles in type 2 diabetes mellitus. Medicine, 95(26), e4088.

10. Sun, J., & Buys, N. (2015). Effects of probiotics consumption on lowering lipids and CVD risk factors: A systematic review and meta-analysis of randomized controlled trials. Annals of Medicine, 47(6), 430–440.

11. Lei, W.-T., Shih, P.-C., Liu, S.-J., Lin, C.-Y., & Yeh, T.-L. (2017). Effect of Probiotics and Prebiotics on Immune Response to Influenza Vaccination in Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients, 9(11), 1175.

12. Hoveyda, N., Heneghan, C., Mahtani, K. R., Perera, R., Roberts, N., & Glasziou, P. (2009). A systematic review and meta-analysis: probiotics in the treatment of irritable bowel syndrome. BMC Gastroenterology, 9(1), 15.

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15. Goldenberg, J. Z., Yap, C., Lytvyn, L., Lo, C. K.-F., Beardsley, J., Mertz, D., & Johnston, B. C. (2017). Probiotics for the prevention of Clostridium difficile-associated diarrhea in adults and children. Cochrane Database of Systematic Reviews.

16. McFarland, L. V. (2006). Meta-Analysis of Probiotics for the Prevention of Antibiotic Associated Diarrhea and the Treatment of Clostridium difficile Disease. The American Journal of Gastroenterology, 101(4), 812–822.

17. McFarland, L. V. (2007). Meta-analysis of probiotics for the prevention of traveler’s diarrhea. Travel Medicine and Infectious Disease, 5(2), 97–105.

18. Hao, Q., Lu, Z., Dong, B. R., Huang, C. Q., & Wu, T. (2011). Probiotics for preventing acute upper respiratory tract infections. In B. R. Dong (Ed.), Cochrane Database of Systematic Reviews. Chichester, UK: John Wiley & Sons, Ltd.

19. Ganji-Arjenaki, M., & Rafieian-Kopaei, M. (2018). Probiotics are a good choice in remission of inflammatory bowel diseases: A meta analysis and systematic review. Journal of Cellular Physiology, 233(3), 2091–2103.

20. Dong, J.-Y., Szeto, I. M. Y., Makinen, K., Gao, Q., Wang, J., Qin, L.-Q., & Zhao, Y. (2013). Effect of probiotic fermented milk on blood pressure: a meta-analysis of randomised controlled trials. British Journal of Nutrition, 110(07), 1188–1194.

21. Khalesi, S., Sun, J., Buys, N., & Jayasinghe, R. (2014). Effect of Probiotics on Blood Pressure: A Systematic Review and Meta-Analysis of Randomized, Controlled Trials. Hypertension, 64(4), 897–903.

22. Collado Yurrita, L., San Mauro Martín, I., Ciudad-Cabañas, M. J., Calle-Purón, M. E., & Hernández Cabria, M. (2014). Effectiveness of inulin intake on indicators of chronic constipation; a meta-analysis of controlled randomized clinical trials. Nutricion Hospitalaria, 30(2), 244–252.

23. Huang, R., Wang, K., & Hu, J. (2016). Effect of Probiotics on Depression: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients, 8(8), 483.

24. Zhong, C., Qu, C., Wang, B., Liang, S., & Zeng, B. (2017). Probiotics for Preventing and Treating Small Intestinal Bacterial Overgrowth. Journal of Clinical Gastroenterology, 51(4), 300–311.

25. Azad, M. A. K., Sarker, M., Li, T., & Yin, J. (2018). Probiotic Species in the Modulation of Gut Microbiota: An Overview. BioMed Research International, 2018, 1–8.

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28. O’Mahony, S. M., Clarke, G., Borre, Y. E., Dinan, T. G., & Cryan, J. F. (2015). Serotonin, tryptophan metabolism and the brain-gut-microbiome axis. Behavioural Brain Research, 277, 32–48.

29. Scott, K. P., Martin, J. C., Duncan, S. H., & Flint, H. J. (2014). Prebiotic stimulation of human colonic butyrate-producing bacteria and bifidobacteria, in vitro. FEMS Microbiology Ecology, 87(1), 30–40.

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33. Fuentes-Zaragoza, E., Sánchez-Zapata, E., Sendra, E., Sayas, E., Navarro, C., Fernández-López, J., & Pérez-Alvarez, J. A. (2011). Resistant starch as prebiotic: A review. Starch – Stärke, 63(7), 406–415.

34. Maccaferri, S., Klinder, A., Cacciatore, S., Chitarrari, R., Honda, H., Luchinat, C., … Costabile, A. (2012). In vitro fermentation of potential prebiotic flours from natural sources: Impact on the human colonic microbiota and metabolome. Molecular Nutrition & Food Research, 56(8), 1342–1352.

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36. Leroy, F., & De Vuyst, L. (2014). Fermented food in the context of a healthy diet. Current Opinion in Clinical Nutrition and Metabolic Care, 17(6), 574–581.

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38. Cummings J.H., & Macfarlane, G. T. (2002). Gastrointestinal effects of prebiotics. British Journal of Nutrition, 87(6), 145–151.

39. Marteau, P., & Flourié, B. (2001). Tolerance to low-digestible carbohydrates: symptomatology and methods. British Journal of Nutrition, 85(S1), S17–S21.

40. Marteau, P., & Seksik, P. (2004). Tolerance of probiotics and prebiotics. Journal of Clinical Gastroenterology, 38(6 Suppl), S67–S69.