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Microbiome, Probiotics, Prebiotics, Fibre and Resistant Starch

What are they and why do we need them?


Your microbiome is the entire genome (genes and DNA) of all our microbes which live primarily in our gut but also include skin, lungs and many other areas. Our gut contains bacteria, viruses, fungi and archaea contributing around an estimated 100 trillion microbes with at least 1000 species of bacteria.2 The microbiome plays an essential role in digestion with energy metabolism, the production of short-chain fatty acids, vitamin synthesis, and fat storage, while playing key roles in pathogen defence, critical for normal immune function, and fascinatingly it can influence human behaviour.2 Gut microbes have also been shown to influence diet as well as anxiety, depression, hypertension and a variety of other conditions. Loss of this rich diversity in the gut is a signal of poor health and can be linked to poor diet, smoking, alcohol, disease states, and antibiotic use. Probiotics and prebiotics can play a beneficial role in our gut promoting positive health outcomes.

What is Microbiota?

Your microbiota is better described as a localised area or habitat of microbes being investigated.

What are Prebiotics?

Through complex carbohydrates, and a combination of fibre and resistant starch these non-digestible food components or ‘prebiotics’ feed the good gut bacteria. Our bodies do not digest them. All prebiotics are plant fibre but not all fibre is prebiotic. Prebiotics are especially found in fruit particularly the skin, vegetables, legumes, nuts, seeds and grains. Some of your best choices are leeks, asparagus, chicory, Jerusalem artichokes, garlic, onions, wheat, uncooked oats, and soybeans but a diverse multicoloured diet high in vegetables, a couple of pieces of fruit per day, occasional legumes, nuts, seeds, grains may be your best bet. Because everyone’s gastrointestinal tract vastly differs, you’ll need to discover what works for you until science can shed conclusive evidence. The recommended amount of vegetables per day is between 5 and 6 serves of around 75g per serve and this includes legumes.

The recommended amount of fruit is two serves of 150g (so 300g fresh whole fruit with the skin!), or 125ml fruit juice (no added sugar), or 30 g dried fruit. For grains (cereal) foods it can be anywhere between 4-9 serves, depending on your needs, and goals. One slice of bread, ½ cup cooked rice/pasta, or ¼ cup of muesli is one serve.

What are Probiotics?

Probiotics are live organisms that we ingest that are reportedly beneficial to our gastrointestinal tract for the maintenance of good health. They are more often used in prevention instead of treating an existing disease, but science is looking at applications for probiotics to be used to treat conditions. Even though they are increasingly common the mechanisms are not well understood.

Where do you find Probiotics?

Probiotics are readily available in many fermented foods which have been eaten for 1000s of years. These include yoghurt, fermented milk drinks like Kefir and Filmjolk, fermented legumes or grains like Tempeh or Miso. Fermented vegetables like Kimchi, Sauerkraut, and the drink Kombucha. They are also marketed, dehydrated in capsules, and even through faecal microbiota transplantation. These capsules are not a prescription and you can find them marketed on social media, TV, through chemists, health food shops, and many practitioners.

Always buy unpasteurised (non-heat treated) fermented vegetables so you get live bacteria. Of course, anything dairy will be pasteurised and then the bacteria added after. According to Crane et al. one particular strain “Lactobacillus rhamnosus has shown a 50% reduction in eczema and significant reductions in other allergic diseases through early childhood”.1

What about supplements?

There is a very wide variety and growing range of supplement brands of probiotics and the number of strains and cocktails grows this list even more. If you think you really need to boost your gut microbiome consider chatting to an accredited practising dietician (APD), registered nutritionist (RNutr) or even your local pharmacist. While they may be considered safe it would be sensible to invest in strains that are going to benefit you.

So, what about fibre?

Majority of experts agree that fibre is absolutely essential for a healthy colon. The Australian Dietary Guidelines suggest between 25-30g of dietary fibre per day, while this is a situation of more does not mean better. Excess fibre may cause constipation or diarrhoea and the opposite may be true too.

Here’s what fibre does

●      Feeds the good gut bacteria

●      Regulates, cleans and maintains a healthy bowel environment

●      May stabilise blood glucose levels due to slower digestion or non-digestible fibre or starch

●      Helps to lower serum cholesterol

●      Slows the emptying process so you absorb more nutrients

●      Improves stool quality

●      May assist in preventing some diseases such as diabetes, heart disease and bowel cancer

Where do I get fibre?

Fibre is found wherever carbohydrates are found. They are contained in fungi and plant foods- fruits, vegetables, grains, beans, legumes, nuts and seeds. Humans and animals convert carbohydrates to energy, and the fibre which is not digestible within helps to keep the digestive system healthy. All food is different and contains varying amounts and types of fibre which can also change depending on whether it is cooked or raw.

What is resistant starch?

This non-digestible starch travels through to your large colon and feeds your good gut bacteria which has many benefits that we know while many are yet to be discovered. It can help to improve insulin sensitivity (a very good thing), and in turn reduce your chances of metabolic syndrome, type 2 diabetes, obesity, heart disease and Alzheimer’s. There are four main types.

●      Found in grains (raw oats), seeds and whole grains

●      Formed when rice, pasta, bread, tortilla or potatoes are cooked and then cooled

●      In raw potatoes and green bananas

●      Man-made synthetic varieties

In summary, your gut is at its healthiest when

●      It can synthesise all the vitamins you need

●      It can rally against intruders such as influenza

●      It lowers inflammation to prevent toxic carcinogens

●      It has an immune-boosting effect

●      A return of the bodies ‘normal’ after antibiotics, disruption and sickness

●      It sends messages to the brain and helps regulate metabolism and mood, which can also influence cognition


[1] Crane J, Barthow C, Kang J, Hood F, Stanley T & Wickens K. Probiotics for humans: Hoax, hype, hope, or help. Journal of the Royal Society of New Zealand [Internet]. 2019 Nov 17 [cited 2020 Sep 20];50(3):456-469. Available from: (2020)

[2] Amon P, Sanderson I. What is the microbiome? Arch Dis Child Educ Pract Ed [Interent].

2017[cited 2020 Sep 20];102(5):257-260. Available from:


National Health and Medical Research Council. Dietary fibre. Updated 2019 May 9 [Accessed 2020 Sep 20]. Australian Government. Available from:

Slavin J. Fiber and prebiotics: Mechanisms and health benefits. Nutrients. 2013 Apr 22;5(4):1417-35. Available from:


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