BLOG BY Charlotte Green, BSc

What Are Prebiotics & Probiotics

There is now significant evidence to suggest that looking after our gut is an integral part of maintaining good overall health. In particular, we must nourish the trillions of microorganisms that form the intestinal microbiota. There are over 1000 different species of bacteria living in the colon that perform essential functions in our bodies (1). It is thought that an imbalance in the microbiota, causing a reduction in so-called “good” bacteria, could contribute to conditions such as IBS, obesity, and some autoimmune disorders such as coeliac disease (2). As a result, the gut microbiota has become a target for improving health.

The terms “prebiotics” and “probiotics” are now popular buzzwords associated with the gut microbiota, particularly in health and wellness spheres, but the vast amounts of information can be difficult to navigate. This article will deal with both individually to provide simple answers to the most frequently asked questions such as:

• What is the difference between PREbiotics and PRObiotics?

• Where can you get them from?

• Should we be taking a supplement?

Prebiotics - what are they?

Prebiotics are non-digestible food ingredients that have been shown in trials to have a beneficial impact on health (3). Although they are a type of dietary fibre, not all fibres are classed as a prebiotic as there is a strict criteria that must be fulfilled.

A prebiotic must:

• Be resistant to the acidic conditions of the stomach

• Remain undigested until it reaches the colon

• Be fermented by the intestinal microbiota

• Change the growth or activity of the microbiota (4)

How do they work?

Prebiotics act as an energy source for the intestinal microbiota, allowing the number of “good” bacteria to thrive (4). These include species of Lactobacillus, that help to resist infections and may play a role in relieving IBS; and Bifidobacteria, which produce B vitamins and help to restore a normal intestinal microbiota after antibiotic treatment (5). 

Prebiotics are digested by gut microbes to produce various beneficial compounds, including short chain fatty acids (SCFAs). SCFAs can travel in the bloodstream, affecting various organs, meaning the consumption of prebiotics can confer a number of health benefits around the body (4).

SCFAs are responsible for:

• Decreasing the number of harmful bacteria in the colon, therefore reducing the risk of infection (3).

• Increasing the absorption of calcium by lowering the pH in the colon, which increases the bioavailability of calcium (1)

• Regulating appetite as the SCFA propionic acid activates the release of hormones that signal when you are full (1). 


The most beneficial prebiotics are inulin, fructo-oligosaccharides (FOS), and galacto-oligosaccharides (GOS) (4), which can be easily found in a variety of plant foods. These include leeks, chicory, bananas, artichokes, onions, garlic, and oats (3). However, some food products, such as breakfast cereals, have been fortified with prebiotics, like inulin (1). Prebiotic supplements are available, yet they are rarely necessary (6), because there are so many food sources available that also offer additional health benefits. This is particularly important to remember because good health cannot be obtained by the consumption of a single nutrient: diversity is the key.  

Probiotics - what are they?

The word “probiotic” comes from Greek, meaning “for life” (7). They are live microorganisms, either bacteria or yeast, that confer a health benefit to us, when consumed in the right quantities (8). The beneficial effects of foods with live microbes has been recognised for centuries, but more gold standard scientific studies are needed to conclusively determine their health benefits (9). Nevertheless, in this era of self-care and complementary medicine, there is growing interest in probiotics, but are they a necessary addition to our health regimes?


There are hundreds of probiotic strains available (8), meaning there is huge variety between the different probiotic products available. Each strain can have different effects on the body, meaning they may not always be useful, unless it is matched to a specific condition.

Probiotics are available as yoghurt drinks and supplement capsules. There is evidence to suggest that capsules may be more reliable as the live microbes are more likely to survive until they reach the colon where they can colonise (10). They are also available as either a single strain or a mixture of different types, which could be more effective. It has been suggested that the different strains are able to work together synergistically to provide a range of health impacts (11).

Fermented foods

Certain fermented foods may contain probiotics, and they are certainly easy to incorporate into the diet. However, there is limited clinical evidence, apart from for fermented dairy, about how they impact the gut (12). Also, it is worth noting that some of the processes used in preparing the products may actually kill the microbes (12).

Nevertheless, including them in the diet may offer some gut health benefits, but will certainly add some extra nutrients and delicious flavours. Some examples of fermented foods include:

• Kefir

• Kombucha (fermented tea)

• Sauerkraut

• Kimchi

• Miso (8)

How do they work?

Probiotics have the potential to confer several health benefits by changing the balance of the gut microbiota. They increase the number of good bacteria, whilst decreasing the number of harmful bacteria, due to competition for space and nutrients (7). This helps to reduce infection risk; and the production of short chain fatty acids by the protective bacteria can affect other organs by reducing inflammation (8).

Should we include a probiotic in our diet?

Currently, due to the growing interest in gut health in the wellness industry, many people with good general health, rather than those with specific health concerns, are taking probiotics, in the hope of boosting their health (13). However, there is limited evidence to suggest that probiotics can offer a significant improvement to general health because so many other factors contribute to good gut health. These include:

• Diet diversity

• Sleep

• Stress

• Exercise

• Age

• Medication (8)

Due to the lack of conclusive evidence, the European Food Safety Authority (EFSA) have not approved any health claims concerning probiotics. This means that all product labelling with the term “probiotics” is currently banned (14).

Nevertheless, probiotics could be an effective therapy option for certain health conditions if the correct strain is consumed in the right quantity. The strongest evidence is for the treatment of antibiotic associated diarrhoea and the prevention of travellers’ diarrhoea (15), as it improves the balance of bacteria in the gut (8) and stimulates the immune system (10). Furthermore, there is some evidence to suggest that probiotics may help to relieve some of the symptoms of IBS as this can be caused by an imbalance in the microbiota (9), but it is still unclear which strains are most effective (8).

In summary, if you are generally healthy, there seems to be no additional benefits to taking a probiotic. Good gut health can be achieved by eating a balanced and varied diet, with as many different plants as possible. Despite this, there are certain medical conditions where a probiotic may be considered. However, because there are so many strains available that affect the body differently, advice should always be taken from a qualified dietitian.

This post was written by Charlotte Green who is a second-year undergraduate at Durham University studying Biological Sciences. She is fascinated by the gut microbiome and the role of nutrition in health, so hopes to pursue a Master's degree in Dietetics when she graduates. Charlotte is also part of The Ugly Fruit Group, a Durham based project aiming to tackle food waste by donating to food banks and creating healthy snacks from surplus fruit and veg. 


(1)   Brownawell, A.M., Caers, W., Gibson, G.R., Kendall, C.W.C., Lewis, K.D., Ringel, Y., Slavin, J.L. (2012), ‘Prebiotics and the health benefits of fibre: current regulatory status, future research and goals’, The Journal of Nutrition, Volume 142, Issue 5, pp. 962-974

(2)   Verbeke, K.A., Boobis, A.R., Chiodini, A., Edwards, C.A., Franck, A., Kleerebezem, M., Nauta, A., Raes, J., van Tol, E.A.F., Tuohy, K.M. (2015), ‘Towards microbial fermentation metabolites as markers for health benefits of prebiotics’, Nutrition Research Reviews, Volume 28, Issue 1, pp. 42-66

(3)   British Nutrition Foundation (2018), Functional Foods, British Nutrition Foundation, viewed 24/08/20, which can be found here

(4)   Davani-Davari, D., Negahdaripour, M., Karimzadeh, I., Seifan, M., Mohkam, M., Masoumi, S.J., Berenjian, A., Ghasemi, Y. (2019), ‘Prebiotics: definition, types, sources, mechanisms and clinical applications’, Foods, Volume 8, Issue 3

(5)   Scantlebury Manning, T., Gibson, G.R. (2004), ‘Prebiotics’, Best Practice and Research Clinical Gastroenterology, Volume 18, Issue 2, pp. 287-298

(6)   Rossi, M (2019), Eat yourself healthy, Penguin Life, UK

(7)   Sarkar, S. (2013), ‘Probiotics as functional foods: documented health benefits’, Nutrition and Food Science, Volume 43, Issue 2, pp.107-115

(8)   Hannan, M. (2019), Probiotics, The Food Medic, viewed 26/08/20, <https://thefoodmedic.co.uk/2019/03/probiotics/>

(9)   Williams, N.T (2010), ‘Probiotics’, American Journal of health-system pharmacy, Volume 67, Issue 6, pp. 449-458

(10) Hamilton-Miller, J. (2004), ‘Probiotics: health benefits for the over 50s’, Nutrition Bulletin, Volume 29, Issue 4, pp. 353-355

(11)Chapman, C.M.C., Gibson, G.R., Rowland, I. (2011), ‘Health benefits of probiotics: are mixtures more effective than single strains?’, European Journal of Nutrition, Volume 50, Issue 1, pp. 1-17

(12)Rossi, M. (2019), Fermented foods, The Gut Health Doctor, viewed 26/08/20, <https://www.theguthealthdoctor.com/all-articles/fermented-foods>

(13)Watson, B., Moreira, D., Murtagh, M. (2009), ‘Little bottles and the promise of probiotics’, Health: An interdisciplinary Journal for the social study of Health, Illness and Medicine, Volume 12, Issue 2, pp. 219-234

(14)Rijkers, G.T., de Vos, W.M., Brummer, R.J., Morelli, L., Corthier, G., Marteau, P. (2011), ‘Health benefits and health claims of probiotics: bridging science and marketing’, British Journal of Nutrition, Volume 106, Issue 9, pp. 1291-1296

(15)Mizock, B.A. (2015), ‘Probiotics’, Disease-a-month, Volume 61, Issue 7, pp. 259-290

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