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Probiotics is a hot topic at the moment as gut health has come into the spotlight. Dietitian Kaitlin Colucci summarises all you need to know about probiotics - what are they, who should take them and what to consider when choosing a probiotic.

What are probiotics?


Probiotics are a combination of live beneficial bacteria and/or yeasts that are promoted as having various health benefits. Probiotics are thought to help restore the natural balance of bacteria in your gut, in particular the gut microbiome – the trillions of microbes living inside your large intestine. Everyone’s gut microbiome is unique, like a fingerprint — even twins are different. These microbes are a diverse community, working together to keep the body healthy. There are trillions of microbes in your body and are typically a combination of:

  • Bacteria
  • Fungi (including yeasts)
  • Viruses
  • Protozoa

Probiotics are usually added to yogurts or taken as supplements and are often described as ‘good’ or ‘friendly’ bacteria. You may see these products labelled as containing ‘live cultures’. There are three main criteria to fulfil the probiotic definition:

  1. The microbes have to be alive
  2. They have to be present in large numbers
  3. They have to have evidence of a health benefit

Though there are many types of bacteria that can be considered probiotics, there are three types of bacteria that have the most research behind them including Lactobacillus, Bifidobacterium, and Saccharomyces boulardii which is why they are most often used in supplements/food products.

Probiotics in food products


The range of food products containing probiotic strains or ‘live cultures’ is wide and still growing. The main products existing in the market are dairy based products. You may see other products such as cereals or snack bars. However, often these products do not provide any benefit to gut health for several reasons.

  1. Unless a product has had additional ingredients added such as saturated fat, added sugars and food additive emulsifiers, which somewhat contradicts the gut health goal, the bacteria is unlikely to survive digestion by the stomach acid.
  2. Probiotic strains are very specific as each strain does different things. Having a random probiotic in a food product hasn’t been shown to help when looking at gut health benefits, even if it does ‘survive’ the stomach acid.
  3. What must also be considered is managing to maintain the viability of the bacteria after processing, packaging and storage conditions, all of which have an impact on the effectiveness of the bacteria. By the time it reaches the consumer and then goes through digestion, it is unlikely to have much benefit on gut health.

Who needs to take a probiotic?


Probiotics are not essential for good health. But if you suffer from a particular gut symptom then there may be some evidence for taking a probiotic. It is important to mention that each strain of probiotic bacteria work in different way, and therefore it is recommended to ensure you are taking the right strain of bacteria to help with the particular symptom you are aiming to manage.


If thinking about taking a probiotic, here’s some things to think about:

  1. Is there evidence for your symptoms?
  2. Which microbes have shown benefit?
  3. What is the effective dose?
  4. How long does it take to see benefit?
  5. Is there a reliable probiotic on the market?
  6. How should it be consumed?

The most evidence we actually have is for the use of probiotics to prevent antibiotic-associated diarrhoea and travellers diarrhoea.

Antibiotic associated diarrhoea


Mild or severe episodes of diarrhoea are a common side effect of antibiotic treatment as the normal healthy gut bacteria tend to be suppressed, which allows the overgrowth of opportunistic bad bacteria. There are many studies which have confirmed a reduced risk of antibiotic-associated diarrhoea (1,2). In particular, a recent meta-analysis (3) (a large review of all clinical trials) which looked at all the evidence on probiotics for the prevention and treatment of antibiotic-associated diarrhoea found that using the probiotics, namely L. rhamnosus, L. casei, and the yeast S. boulardii, (as these are the probiotics predominantly included in the majority of trials) is associated with a reduced risk of antibiotic-associated diarrhoea. However, more research is still needed to determine the optimal dose of the probiotic. It is typically recommended to take a probiotic for the duration of the antibiotic course, plus an additional two weeks afterwards.

Travellers’ diarrhoea


Several studies have investigated the efficacy of probiotics in the prevention of travellers' diarrhoea in adults. However, results are quite mixed due to differences in the populations studied, the type of probiotic being investigated, the given dose of probiotic, as well as the destination to which travelled, and personal compliance to taking the probiotic. Despite this, some studies have shown that L. rhamnosus GG, S. boulardii, L. acidophilus, and B. bifidum seem to have the most significant result (4,5,6).

Key things to consider


Some other things to think about if you’re taking a probiotic as a supplement

  • Don’t take a probiotic thinking it’ll be a quick fix for your symptoms. Address underlying nutrition and lifestyle factors first.
  • If you do take a probiotic, trial it for 4 weeks and if your symptoms don’t improve then stop. Even if it’s good quality, it might not be right for you - remember our gut microbiome is like a fingerprint, so what works for one person, might not work for you.
  • Dose and how to take it matters - often clinical trials have looked at a specific dose of probiotic or taken with or without food to see a clinical benefit.
  • If you’re thinking of taking a probiotic for a specific condition, speak to a Dietitian or Registered Nutritionist who can provide some guidance if you can.



Prebiotics, not to be mistaken for probiotics, are the foods that feed your gut bacteria. Most prebiotics are a type of dietary fibre, although not all fibres are prebiotics. This is because for a dietary fibre to ‘win’ a prebiotic title, it must show a health benefit in several scientific trials.


The main prebiotics include:

  • Inulin
  • Fructo-oligosaccharides (FOS)
  • Galacto-oligosaccharides (GOS)

Prebiotics are fermented by the gut bacteria and produce short-chain fatty acids, e.g. propionate, butyrate, and acetate. The benefit of this has ranged from improving blood-sugar control, to regulating appetite, and supporting bone and skin health (6).


There is no need to take a prebiotic supplement however, as many foods are rich in prebiotic fibres. The main sources include:

  • Fruit – Apricots, dates, grapefruit, pomegranate, watermelon, dried mango
  • Vegetables – Artichokes, asparagus, beetroot, fennel bulb, garlic, leeks, onion
  • Grains & nuts – Almonds, barley, cashews, hazelnuts, pistachios, rye, spelt
  • Others – Black beans, butterbeans, chickpeas, chai tea, chamomile tea



Although probiotics can be useful for some, they are not necessary for everyone. Nothing beats a varied diet rich in plant-based foods to feed your gut what it needs.



  1. McFarland LV. (2016) Meta-analysis of probiotics for the prevention of antibiotic associated diarrhea and the treatment of Clostridium difficile disease. American Journal of Gastroenterology. 101(4):812–822.
  2. Sazawal S, Hiremath G, Dhingra U, Malik P, Deb S, Black RE. (2006) Efficacy of probiotics in prevention of acute diarrhoea: a meta-analysis of masked, randomised, placebo-controlled trials. The Lancet Infectious Diseases. 6(6):374–382.
  3. Hempel S, Newberry SJ, Maher AR, et al. (2012) Probiotics for the prevention and treatment of antibiotic-associated diarrhea a systematic review and meta-analysis. The Journal of the American Medical Association. 307(18):1959–1969.
  4. McFarland LV. (2007) Meta-analysis of probiotics for the prevention of traveler’s diarrhea. Travel Medicine and Infectious Disease. 5(2):97–105.
  5. Marteau P, Seksik P, Jian R. (2002) Probiotics and intestinal health effects: a clinical perspective. British Journal of Nutrition. 88(1):S51–S57.
  6. Hilton E, Kolakowski P, Singer C, Smith M. (1997) Efficacy of Lactobacillus GG as a diarrheal preventive in travelers. Journal of Travel Medicine. 4(1):41–43
  7. Oniszczuk A, Oniszczuk T, Gancarz M, Szymanska J (2021) Role of Gut Mircrobiota, Probiotics and Prebiotics in the Cardiovascular Diseases. Molecules. 26, 1172.

Kaitlin Colucci

Gut health dietitian

IG: @themissiondietitian

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