Probiotics and prebiotics: what you need to know

As a dietitian, I spend a lot of time thinking – and talking – about guts. Mine, yours, everyones. And while it may not be the best dinner table conversation, it’s high time we all have a think about what our daily routine is doing to our insides. And, you can’t think about the gut without considering the 2kg of microorganisms which reside there, known as your gut microbiome.

Everyone has a unique mixture of gut microorganisms which help with digestion, vitamin B and K production and the immune system. It is affected by the environment, nutrition, stress, medications and disease.

If you’re interested in improving the health of your gut, you’ll have no doubt heard about probiotics and prebiotics. But what exactly are they?


Probiotics are live microorganisms which are found in foods. They assist the gut microbiome with digestion, including the production of vitamins and fatty acids, and are critical for normal immune system development. They also take up the prime real estate so harmful strains of bacteria have a tougher time taking over.


  • Sauerkraut
  • Kefir
  • Kimchi
  • Yoghurt
  • Some cheeses
  • Sour cream


Prebiotics are non-digestible food ingredients that can increase the activity of probiotics. They act as the food for probiotics, which makes the probiotic more effective. They are mostly found in foods which are high in fibre.


  • Asparagus
  • Leeks
  • Bananas
  • Raw onion and garlic
  • Wholegrains like wheat, rye, barley and oats.

Overall, taking a probiotic is a great step to take in increasing the friendly bacteria in your gut. Probiotics can assist with:

Antibiotic associated diarrhoea

Taking probiotics alongside antibiotics reduces the risk of diarrhoea. Strains which have evidence about being successful include Lactobacillus rhamnosus GG, L.acidophilus (found in yoghurt), L. caseii and Saccharomyces boulardii (a yeast).

Irritable bowel syndrome

Some studies that show benefit from probiotics reducing symptoms of IBS but there is more research in this area needed to work out strain and dosage. IBS symptoms are very individualised so treatment would vary.


There are various mechanisms where probiotics may play a role in reducing illness severity or duration, however there is not enough evidence from large, well designed, dependant studies to prove this. 

Traveller’s diarrhoea

Some studies have found taking probiotics while travelling can reduce the risk of travellers’ diarrhoea.


To summarise, probiotics have a lot of potential to have some very interesting effects on our health. The issue that we currently face is that there are a lot of different strains and each product varies massively, making it difficult for professionals to make accurate recommendations.

Hopefully as interest increases in this area, more evidence will emerge as to exactly which probiotic we should be taking.