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The low-down on probiotics, prebiotics and synbiotics

Last updated on June 18th, 2019

The impact that gut health has on overall health never ceases to amaze me, and the bacteria living in the gut is an important part of this. We have anywhere from one to three kilograms of bacteria residing in our large intestine, and this is collectively known as the gut microbiome. It could almost be considered an organ given its vital role in so many aspects of human health. From digestion to immune function, to our mood and our body shape and size, a healthy gut bacteria profile is key.

It’s therefore not surprising that people want to enhance their gut health (who wouldn’t, considering how central it is to every aspect of our health!). And it’s not surprising that companies want to create food and supplement products to help us do this. Probiotics, prebiotics and synbiotics are three such products that are often confused despite playing different roles for gut health. So what are they and are they worth your while?


Probiotics are beneficial bacteria. Or, more specifically, they are live microorganisms that benefit the host (you) when consumed in adequate amounts.

For probiotic supplements to have any potential benefits, they must be scientifically proven to survive digestion (meaning they need to survive exposure to stomach acid) and reach the large intestine alive. They also need to be in a sufficiently high dose to have an effect, plus the pH level of the local environment (inside the intestines) needs to be appropriate for the bacteria. Whether or not a probiotic supplement is scientifically proven to survive digestion is therefore an important consideration – in other words, the quality of the supplement matters.

But there isn’t just one universal probiotic. Different strains of bacteria have different actions and health benefits, and the actions of a particular strain cannot be extrapolated to other strains, even within the same species. So supplements can contain different probiotic strains as well as different doses of the strains, which influences their effect in the body. Adding to this complexity is the fact that we don’t all respond to probiotic supplementation in the same way – our individual response can depend on the species that are already residing in our gut, as well as our own health status.

Research has shown that within about two weeks of ceasing probiotic supplementation, the strains that were present in the supplement are no longer detectable in the waste leaving the body, indicating that they don’t colonise the gut and therefore may not have long-lasting effects.

We know that our gut microbiome is greatly impacted by our food choices, so rather than supplementing probiotics, I prefer to encourage people to focus on eating real whole foods (including some fermented foods) to support and maintain a healthy gut bacteria profile.

Probiotic supplements aren’t necessarily needed for good gut health, however there is some encouraging evidence that suggests they can be beneficial for certain gut conditions:

Antibiotic-associated diarrhoea

There is good evidence that certain strains of probiotics can help to prevent antibiotic-associated diarrhoea; specifically Lactobacillus rhamnosis GG (LGG) and Saccharomyces boulardii (S. boulardii).

Irritable bowel syndrome (IBS)

There is emerging evidence that probiotics may reduce IBS symptom severity. However, given that IBS can manifest as different symptoms depending on the person, probiotics are unlikely to be a magic fix and a probiotic supplement may or may not benefit you. What helps one person may not help another, and in fact, could actually worsen their symptoms. If you decide to trial a particular probiotic supplement, it should be taken for at least four weeks to assess how it affects you. Remember, your body is your best barometer.

However, if you have IBS and you are currently in the elimination or challenge phases of a low FODMAP diet, I do not recommend taking a probiotic supplement, as this could cloud your results and make it more difficult to identify which (if any) of the high FODMAP foods you react to.

Ulcerative Colitis

In patients with mild to moderately active ulcerative colitis, studies suggest that specific probiotics may help to induce and maintain remission. The specific probiotics that may assist include E. Coli Nissle 1917 and a mixture of eight strains, similar to those showing promise in IBS.

Generally, probiotics are safe for adults to take, however those with food allergies should always check that the probiotic is free from their specific allergen, and they shouldn’t be taken by immunocompromised or critically ill people unless medically supervised. 


Prebiotics are non-digestible carbohydrates that act as food for probiotic bacteria. They pass through the gastrointestinal tract undigested, which stimulates the growth and/or activity of certain ‘good’ bacteria in the large intestine. While all prebiotics are considered fibre, not all fibre has prebiotic effects.

Prebiotics are naturally present in foods such as onion, garlic, leeks, asparagus, Jerusalem artichokes, chickpeas, lentils, peas, oats and cashews – yet another reason why a plant-rich way of eating is so important for our health and wellbeing. While some people choose to take a prebiotic supplement if they do not consume enough prebiotic-containing foods, there is no substitute for a ‘real food’ way of eating when it comes to our health and vitality.


Synbiotics is the term used to describe a food or supplement that contains both probiotics and prebiotics; a food example is unpasteurised sauerkraut.

In summary, if you already take a probiotic and feel you benefit from it, then by all means continue to do so. I simply wanted you to appreciate yet another health-enhancing offering of eating whole, real foods.

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