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Prebiotics vs probiotics - what's the difference?

Prebiotics and probiotics may sound similar, but did you know they play different roles in your health?

Bacteria often get a bad name. We may associate the term with infection or disease, but this is not always true.

Probiotics and prebiotics can both strengthen and diversify the bacteria in our bodies. Some of these bacteria are commensal where, not only are they harmless, but actually beneficial, producing various nutrients, protecting us from infiltration by other disease-causing bacteria, and regulating a normal immune response [1][2].

But first, it’s helpful to understand the role of our gut microbiota.

Gut microbiota

About 100 trillion microorganisms line our gastrointestinal tracts. They are termed the gut flora or microbiota. This mini ecosystem, primarily comprised of bacteria, supports the growth of other specialist microbes that release short chain fatty acids (SCFAs) [3]. SCFAs have many important functions:

  • Regulate lipid and glucose levels
  • Act as an energy source for intestinal cells
  • Contribute to healthy gut lining and mucosal barrier
  • Modulate appetite
  • Regulate immune system and inflammatory responses
  • Anti-cancer and anti-inflammatory properties [4]

Unsurprisingly, an imbalance of these gut flora can directly impact our health. People with obesity, diabetes, coeliac disease, inflammatory bowel disease, atopic eczema and arterial stiffness generally have reduced bacterial biodiversity [3]. This indicates a link between gut biodiversity and our general health. But how do we alter or diversify our microbiota?

Fortunately, something as simple as modifying our diet can have a profound and rapid effect (within 24 hours) on the composition of bacteria that make up our gut flora [5]. This is where probiotics and prebiotics come in.

To put it simply, if our gut flora were an army, probiotics would recruit more soldiers and prebiotics would be supplying them with resources, like food and weaponry, to make sure they function at their best and multiply. Let’s look at them both in more detail.

Probiotics

Probiotics are live bacteria and yeasts that, when administered live in adequate amounts, provide a health benefit [3][6]. They can be added to yoghurts or taken as food supplements and must meet safety and functional criteria according to food safety authorities [2].

Human probiotics primarily consist of the following bacterial families: Lactobacillus, Bifidobacterium, Streptococcus, Enterococcus and Lactococcus, though there are many others and even yeasts such as Saccharomyces [2].

Some of the possible health benefits of probiotics include:

  • Reducing frequency and duration of diarrhoea following antibiotics, rotavirus infection and chemotherapy
  • Restoration of natural gut flora after antibiotics
  • Improvement in the efficiency of the immune system
  • Inhibition in the development of harmful gut bacteria (including reduced counts of Coli and H. Pylori)
  • Production of B vitamins and enhanced absorption of other vitamins and minerals
  • Reduction in total cholesterol, fasting blood glucose levels and C reactive protein (an inflammatory marker) [2][3][5]

Probiotics are generally considered a dietary supplement rather than a drug; as such, clinical testing is not always as rigorous. When looking for good sources of probiotics, yoghurts and other fermented foods may be a good place to start, but you should bear in mind that labels stating “live and active cultures” may not necessarily confer health benefits, as per the definition of a probiotic.

Sometimes the number of bacteria (measured in colony forming units) may be insufficient; they may not survive the acidic conditions of the upper digestive tract; or other manufacturing processes, such as high temperatures and pressures, may destroy the live cultures [7][8].

Sources of probiotics

Fermented foods that contain live cultures (but are not necessarily always probiotic) include yoghurts, kimchi, sauerkraut, kombucha, cheeses, miso, pickles, and raw unfiltered apple cider vinegar [9].

Some branded probiotic supplements are beneficial in the treatment of specific gastrointestinal disorders, including Activia, Danactive, Culturelle, and Align [10]. However, it is worth carrying out some research before trusting marketing claims, or at least taking it with a pinch of salt, as some may be biased or unsupported by clinical trials.

Prebiotics

Prebiotics are non-digestible carbohydrate components that specifically stimulate the growth or activity of certain microorganisms [5]. Essentially, they are nutrients that allow the “good bacteria” in our gut to thrive.

Prebiotic consumption has been shown to enrich and increase the number of many types of gut bacteria such as BifidobacteriaLactobacilli, Ruminococcus, E. rectale, and Roseburia [4][5].

Some of the possible health benefits of prebiotics include:

  • Increasing numbers of Bifidobacteria and Lactobacilli in the gut
  • Reducing duration of diarrhoea
  • Enhancing absorption of certain minerals such as calcium
  • Reducing the risk of cardiovascular disease
  • Decreasing harmful bacteria populations
  • Improving immune system efficiency [11][12]

Prebiotics may be used as an alternative to probiotics or taken in conjunction. Products containing both can have a beneficial additive effect compared to taking a prebiotic or probiotic alone. These may be termed “synbiotics” as they work together [2].

Sources of prebiotics

Sources of prebiotics include soybeans, unrefined wheat and barley, raw oats, bananas, garlic, chicory roots, leeks and onions [5][13]. Prebiotics, unlike probiotics, are not live cultures. Therefore, although cooking and food manufacture may alter their chemical composition somewhat, it is of less concern than with probiotics [14].

What about postbiotics?

Postbiotics are fairly new in the field of ‘biotics’ and, as such, their definition is still under discussion. They are effectively the end-product of gut flora metabolism and can include small microbial fragments, metabolites and other small compounds [15].

Remember the short-chain fatty acids we discussed earlier? These are an example of a postbiotic and can be administered directly for potential health benefits. They present an exciting opportunity moving forward in the world of gastrointestinal and overall health.

Should I take probiotic or prebiotic supplements?

Probiotics and prebiotics can have significant proven health benefits. Yet, there are many products on the market making claims with little or no clinical evidence. Much of their efficacy depends on the quantity and type of microbial strain, the quality of the product, and how it is stored, which can vary considerably.

In general, prebiotics and probiotic supplements are safe for most individuals to take, however, people who are immunocompromised and people with short gut syndrome should avoid probiotic supplements, or at least discuss with a healthcare professional. Elderly people should also proceed with caution [16].

As with many supplements, their perceived benefits differ between individuals, and something that suits one person may not be right for you. Sometimes trialing products is the best way forward. Helpfully, the World Gastroenterology Organisation has provided an evidence-based list of probiotics that may be beneficial for certain conditions.

The bottom line

Our gut flora plays a vital role in our overall health. One of the ways we can maintain a healthy gut is through consuming prebiotic- and probiotic-rich foods. Supplements are another good source, but it is worth reading the label and any surrounding literature to be sure its claims are valid.

Definitions

  • Probiotics – the “good bacteria” found in the gut and in some foods and supplements. They convert prebiotics into postbiotics which are beneficial to your health.
  • Prebiotics – types of nutrients that ‘feed’ the good bacteria in your gut allowing them to multiply and diversify.
  • Postbiotics – bioactive compounds that are beneficial to your health produced by “good bacteria” after they break down prebiotics.

References

  1. Khan, R., Petersen, F. C., & Shekhar, S. (2019). Commensal Bacteria: An Emerging Player in Defense Against Respiratory Pathogens. Frontiers in immunology10, 1203. https://doi.org/10.3389/fimmu.2019.01203
  2. Markowiak, P., & Śliżewska, K. (2017). Effects of Probiotics, Prebiotics, and Synbiotics on Human Health. Nutrients9(9), 1021. https://doi.org/10.3390/nu9091021
  3. Valdes, A., Walter, J., Segal, E. and Spector, T. (2018). Role of the gut microbiota in nutrition and health. BMJ, 361:k2179 doi:10.1136/bmj.k2179
  4. Thursby, E., & Juge, N. (2017). Introduction to the human gut microbiota. The Biochemical journal474(11), 1823–1836. https://doi.org/10.1042/BCJ20160510
  5. Singh, R.K., Chang, HW., Yan, D. et al. (2017). Influence of diet on the gut microbiome and implications for human health. J Transl Med 15, 73. https://doi.org/10.1186/s12967-017-1175-y
  6. Reid G, Gadir AA, Dhir R. Probiotics: Reiterating What They Are and What They Are Not. Front Microbiol. 2019 Mar 12;10:424. doi: 10.3389/fmicb.2019.00424. PMID: 30930863; PMCID: PMC6425910.
  7. NHS.(2021) Probiotics. [online] Available at: <https://www.nhs.uk/conditions/probiotics/> [Accessed 27 September 2021].
  8. Marco, M.L., Sanders, M.E., Gänzle, M. et al. (2021) The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nat Rev Gastroenterol Hepatol 18, 196–208. https://doi.org/10.1038/s41575-020-00390-5
  9. National Institutes of Health. (2020) Office of Dietary Supplements - Probiotics. [online] Ods.od.nih.gov. Available at: <https://ods.od.nih.gov/factsheets/Probiotics-HealthProfessional/#en3> [Accessed 27 September 2021].
  10. Ciorba M. A. (2012) A gastroenterologist's guide to probiotics. Clinical gastroenterology and hepatology : the official clinical practice journal of the American Gastroenterological Association, 10(9), 960–968. https://doi.org/10.1016/j.cgh.2012.03.024
  11. Pandey, K., Naik, S. and Vakil, B. (2015) Probiotics, prebiotics and synbiotics- a review. Journal of Food Science and Technology, 52(12), pp.7577-7587.
  12. Carlson JL, Erickson JM, Lloyd BB, Slavin JL. (2018) Health Effects and Sources of Prebiotic Dietary Fiber. Curr Dev Nutr. 2018 Jan 29;2(3):nzy005. doi: 10.1093/cdn/nzy005. PMID: 30019028; PMCID: PMC6041804.
  13. Lomax, A. and Calder, P. (2008) Prebiotics, immune function, infection and inflammation: a review of the evidence. British Journal of Nutrition, 101(5), pp.633-658.
  14. Gatlin, D., 2015. Prebiotics. Dietary Nutrients, Additives, and Fish Health, pp.271-281.
  15. Żółkiewicz, J., Marzec, A., Ruszczyński, M. and Feleszko, W., 2020. Postbiotics—A Step Beyond Pre- and Probiotics. Nutrients, 12(8), p.2189.
  16. Shahrokhi M, Nagalli S. Probiotics. In: StatPearls. StatPearls Publishing, Treasure Island (FL); 2020. PMID: 31985927.