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Probiotics and gut health, a digestible summary

Gut health has become a topic of significant focus both in the mainstream media and clinical investigation, and healthcare professionals are finding themselves fielding questions about probiotics more and more frequently. As with all things, it is our responsibility to remain updated on current probiotics research in order to be able to make appropriate recommendations for specific patient populations.


The World Health Organisation (WHO) classifies probiotics as ‘live organisms which when administered in adequate amounts confer a health benefit on the host’.

The Gut Microbiome

To understand probiotics, it is important to first have an appreciation of the roles of the normal intestinal microbiome (commensal microbiota). The human gastrointestinal tract is home to trillions of microorganisms, most of them bacteria, but also viruses, fungi and protozoa. Increasing evidence suggests that gut microbes play an essential role in human health by protecting against pathogen colonisation, facilitating dietary digestion and absorption, synthesising essential vitamins, producing beneficial metabolites (more recently being referred to as postbiotics), maintaining the integrity of the intestinal epithelium3 and regulating immune system development.

Yet, it isn’t exclusively beneficial microorganisms that reside in the gastrointestinal tract. In healthy individuals the ‘good’ and the ‘bad’ microorganisms live in harmony providing beneficial health outcomes. However, when there is an imbalance within the microbiome, there is potential for the beneficial mechanisms to be disrupted, which is known as dysbiosis and can be associated with inflammation and disease.

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Who Would Benefit From a Probiotic?

The marketing of probiotics often suggests that their consumption will simply improve overall health by increasing the number of good bacteria colonised in the gut. Unfortunately, this is misleading. Research has demonstrated that probiotics are not able to colonise in the gut and rarely do they exert any effect on the commensal microbiota. Instead, probiotics are considered helpful visitors who do not improve overall health but rather exert highly individualised health benefits that are dependent on the specific strain.

As health professionals, it is essential to emphasise to patients this highly individualised nature of probiotics. Probiotics are identified by the specific strain of bacteria which includes the genus, the species, the subspecies (if applicable), and an alphanumeric strain designation. Strains of bacteria, even if within the same species, can have significantly different therapeutic actions, properties and characteristics. An analogy that can help patients conceptualise the probiotic classification system is to liken it to different breeds of dogs. All dogs belong to the same genus and species, yet within the species there is a great diversity in behavioural and physical characteristics. A poodle for example is very different to a Rhodesian ridgeback.

Therefore, with these considerations, probiotics would be applicable when there is sufficient clinical research to justify the use of them for relief regarding a specific condition. Currently, there is evidence to suggest probiotics may provide some relief for symptoms of irritable bowel syndrome (IBS) ulcerative colitis, acute infectious diarrhoea, diarrhoea associated with antibiotic use and Clostridium difficile (C.diff) associated diarrhoea.

Selecting the Appropriate Probiotic

There are three things to consider when recommending a probiotic supplement to a patient. First, it is essential to ensure the product contains an adequate number of live organisms, which is referred to as a colony forming unit (CFU). While the exact amount is strain-dependent, the minimum dose for most strains is 109 CFU/day, so when unsure it is best practice to recommend a probiotic product that contains bacteria in concentrations >109 CFU/dose.

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