Prebiotics: what are they, and why are they essential for gut health?

To better understand, we recommend learning 10 Key Terms to Help Understand Gut Health before reading this article!

The gut microbiome plays an essential role in human health. Now, more than ever, there’s growing interest in using dietary approaches to modulate the composition and metabolic function of the microbes in the gastrointestinal tract to help improve health and reduce the risk of several chronic diseases, such as Cardiovascular Disease and Type-2 Diabetes.

Research suggests that the first significant exposure to microbes occurs at birth and depends on whether a baby is delivered vaginally or by Caesarean section and fed breast milk or formula during the initial months of life. Although a human gut microbiome is thought to reach its adult state by age 3, the community of bacteria inhabiting a single microbiome remains malleable in response to environmental, lifestyle, medicinal, and dietary factors throughout a lifetime.

One dietary strategy commonly praised for its ability to help modulate gut microbiota is the consumption of dietary fibres and prebiotics.

What is dietary fibre?

Dietary fibres are edible carbohydrate polymers with three or more monomeric units resistant to endogenous digestive enzymes. Therefore they are neither hydrolysed nor absorbed in the small intestine.

In basic English, dietary fibre translates to the part of plant foods that the human body can’t digest or absorb. Dietary fibres are typically defined as carbohydrates. They remain relatively intact for their entire journey through the digestive system until passing out of the body.

Dietary fibre influences gut microbiota composition and is related to better health, with a high-fibre diet helping to:

  • Normalise bowel movements
  • Maintain bowel health
  • Improve cholesterol levels
  • Control blood sugar levels
  • Support weight management
  • Improve mental health
  • Reduce the risk of certain cancers
  • Encourage good gut health
The four categories of dietary fibre
Soluble fibre

A type of fibre that includes plant pectin and gums that dissolve in water to form a gel-like substance. Soluble fibre helps to slow down digestion, helping to feel fuller for longer, and may improve blood cholesterol and glucose levels.

Soluble fibre is found in many foods, including oats, legumes, apples, citrus fruits, barley and psyllium.

Insoluble fibre

A type of fibre that includes plant cellulose and hemicellulose that doesn’t dissolve in water. Known for its properties in bulking up stools and preventing constipation, insoluble fibre absorbs water, making the contents of the bowel softer so that stools can pass regularly and without strain.

Insoluble fibre is found in whole-grain flour, wheat bran, nuts, seeds, legumes, and the skin of fruit and vegetables.

Resistant starch

Resistant starch essentially ‘resists’ small intestine digestion as it moves through to the large intestine, where it is fermented in the colon. Resistant starch is an essential ‘food’ for the beneficial gut bacteria that make butyrate (a gut metabolite). Butyrate’s key function is to keep the gut lining healthy and functioning normally.

Resistant starch can be formed when certain foods, such as potato, rice and pasta, are cooked and cooled. Chickpeas, kidney beans, navy beans and under-ripe (green) bananas are also great food sources of resistant starch.

Readily fermentable fibre

A newly identified group, readily fermentable fibre is quickly and easily metabolised by intestinal bacteria. However, it releases gases and other by-products that may cause problems for some people with Irritable Bowel Syndrome (IBS) and FODMAP sensitivity. It is suggested that readily fermentable fibre foods should be avoided for people with IBS, particularly when experiencing symptoms.

Key food sources of readily fermentable fibre are legumes, onion, leeks, garlic, Jerusalem artichoke and bananas.

clinical trials, beneficial strains, healthy microbiome


What are prebiotics?

Maintaining the integrity of the original embodiment of prebiotics and an awareness of the latest scientific and clinical developments in the field, the current definition of a prebiotic, according to the International Scientific Association for Probiotics and Prebiotics (ISAPP), is:

“A substrate that is selectively utilised by host microorganisms conferring a health benefit”.

In simple terms, prebiotics are food components or ingredients that are not digestible by the human digestive system; however, they selectively nourish beneficial bacteria in the gut, providing many health benefits to the host.

What are the standard features of a prebiotic?

A substrate is a molecule or substance that conducts a chemical reaction under the influence of an enzyme. For a gut substrate to be labelled a prebiotic, it must pass three tests.

It must be resistant to human digestion.

As a substrate travels through the gastrointestinal tract, it must not be completely broken down by human enzymes, ensuring it reaches the large intestine (also known as the colon) relatively untouched.

It must undergo fermentation by gut microbes.

Once a substrate reaches the large intestine, gut microbiota bacteria must metabolise the substrate using their unique enzymes.

It must selectively encourage the growth of beneficial gut bacteria

Once broken down, the prebiotic substrate must provide nutrients to the good bacteria, inferring health benefits to the host.

Are prebiotics the same as dietary fibre?

No, not all fibres are created equally. Whilst prebiotics are primarily derived from fibre, they are fermentable in the large intestine (colon). In contrast, dietary fibre does not ferment nor digest but instead binds to the body’s waste products to help form a stool and regulate bowel motions.

What are the health benefits of prebiotics?

Several whole-body health benefits occur when prebiotic fibres are metabolised in the large intestine. Some of these benefits to host health include:

Production of short-chain fatty acids (SCFA)

SCFAs have immunomodulatory and anti-inflammatory properties that help improve immunity, aid digestive health, and even balance cholesterol levels.

Regulation of blood sugar levels

Current research indicates prebiotics may help regulate blood sugar levels (glycaemic control) to support diseases such as Type-2 Diabetes.

Improved bone health

Calcium bioavailability and absorption are increased in the large intestine, benefiting healthy bone density and reducing conditions such as osteoporosis.

Improved mental health

Neural, immune and endocrine pathways via the ‘gut-brain axis’ are being scientifically explored to determine the exact mechanisms of function. However, overall results show that prebiotics improve disorders such as anxiety, depression and stress. They are also beneficial in improving cognitive function and sleep-wake cycles.

Better heart health

The gut microbiome can influence cardiovascular conditions through modulating metabolites, such as trimethylamine/trimethylamine N-oxide, SCFA, bile acids, lipopolysaccharides and peptidoglycans.

Reduction in allergy symptoms

Good microbial diversity reduces allergy-type conditions (eczema, allergic reactions etc.) by regulating the inflammatory response.

Improved bowel health and function

Prebiotics improve the lining of the colon wall and ensure this mucosal layer functions properly. This helps with the absorption of vitamins and minerals, and the diffusion of SCFA and other vital metabolites into the bloodstream.

Types of prebiotic foods

Prebiotics can include both fibre and phytochemicals (chemicals from plants). Whilst there are many types of prebiotics, they are predominantly a subset of carbohydrates. Some of the richest sources of prebiotics are plant-based foods, such as whole grains, nuts, seeds, legumes, fruits, and vegetables.

They can be classified into the following categories: fructans, galactooligosaccharides (GOS), starch and glucose-derived oligosaccharides, other oligosaccharides, and non-carbohydrate oligosaccharides.


Fructans are a highly beneficial prebiotic. Consisting of inulin and fructooligosaccharides (FOS), they have either a short or long chain of fructose molecules. However, for people with functional gut disorders, such as irritable bowel syndrome (IBS) and FODMAP sensitivity, fructans, particularly inulin, may cause abdominal pain, bloating, wind, and irregular bowel motions.

Fructans stimulate probiotics in the Lactobacillus and Bifidobacterium species, which help relieve constipation and reduce pathogens (harmful bacteria) in the gut. They are found in asparagus, leek, onion, garlic, wheat and Jerusalem artichoke.

Galactooligosaccharides (GOS)

Galactooligosaccharides greatly influence the probiotic species of Bifidobacteria and Lactobacilli as well as Enterobacteria, Bacteroidetes and Firmicutes. This prebiotic occurs naturally in legumes such as beans, chickpeas and lentils and can also be derived from lactose in dairy products.

Resistant starch and glucose-derived oligosaccharides

The group of resistant starch and glucose-derived oligosaccharides promotes the production of the short-chain fatty acid, butyrate – the primary energy source for human colonocytes (epithelial cells of the colon) that helps to keep the lining of the intestines (mucosal layer) healthy so it can absorb vitamins, water and electrolytes.

Resistant starches are found in lentils, beans, rolled oats, green bananas, and cooked and cooled potatoes and rice.

Other oligosaccharides

Non-starch polysaccharides (POS), such as pectin, are a type of structural fibre typically found in fruit skins. Studies are investigating the health benefits of POS in helping to reduce inflammation and increase beneficial gut bacteria.

Non-carbohydrate oligosaccharides

Phytochemicals have recently been classified as prebiotics due to having the same impact or health effects on gut microbiota. These non-carbohydrate prebiotics are bioactive plant chemicals and can be found in plant foods like berries, plums, herbs, spices, red onions, dark chocolate, and nuts.

Plant-based foods

Plant-based foods, such as whole grains, seeds, nuts, fruits, and vegetables, are loaded with fibre that helps to cultivate diversity in the microbiome and provide gut bacteria with the fibre needed to thrive.

Fibre-rich foods help to prevent chronic constipation (which can cause gut dysbiosis) and regulate inflammatory responses, which support an anti-inflammatory action in many chronic conditions, such as Inflammatory Bowel Disease (IBD), Type-2 Diabetes, some cancers, and heart disease.

Prebiotic supplements

If regular consumption of prebiotic foods isn’t achievable, you may wonder if prebiotic supplements can provide beneficial effects on the human microbiome. And we’re here to confirm that a prebiotic supplement can help improve gut health and overall health.

How to know which prebiotic supplement is right for you

The hallmark of a healthy gut microbiome is diversity, with several studies identifying a lower diversity of gut microbes being linked with certain diseases or symptoms, such as Inflammatory Bowel Disease (IBD) and Crohn’s disease. A balanced composition of gut bacteria beneficially affects bodily functions, like digestion, the absorption and production of essential nutrients, and regulation of immune system function.

Given the variation of gut microbiota and no two people sharing the same combination, it’s best to consume a personalised prebiotic supplement tailored to the current state of your gut microbiome.

Stool microbiome tests enable scientists to analyse and identify any imbalances of good and bad bacteria in your gut and compound personalised blends of prebiotics to address your unique insights. After your gut microbiome baseline has been identified, you can continue to track how your personalised prebiotics assist in cultivating a greater diversity of live microorganisms in the gut.

Learn five reasons to test your gut microbiome with Vidality.

Are prebiotics safe for everyone?

The short answer is yes, but no; there is always an asterisk in the fine print. And when it comes to prebiotics, the asterisk refers to people experiencing functional gut diseases, people experiencing small intestinal bacterial overgrowth (SIBO), people following a low FODMAP diet, and people with gluten intolerance or coeliac disease.

Functional gut diseases

Looking at someone experiencing functional gut diseases, like IBS or IBD, when managing symptoms or in a flare-up, taking prebiotics or eating high-fibre foods can be detrimental until inflammation has eased.

Once symptoms have reduced, fibre intake can slowly be increased, and prebiotics (either prebiotic supplements or foods) can be introduced to increase the diversity and number of healthy bacteria in the gut. This protocol can also help reduce the risk of relapse and promote colon healing.

Small intestinal bacterial overgrowth (SIBO)

A health condition known as small intestinal bacterial overgrowth, or SIBO, occurs when the small intestine becomes overrun by harmful bacteria. Prebiotics, probiotics and high-fibre foods can trigger a worsening of symptoms.

Low FODMAP diet

Eating enough fibre (and prebiotics) on a low FODMAP diet can be a challenge. Many prebiotic food sources may cause gut-related symptoms. Some FODMAP-friendly prebiotic foods are beetroot, butternut pumpkin, oats, cooked and cooled pasta, and canned lentils and chickpeas. People following a low FODMAP diet can also consider a personalised prebiotic supplement.

Gluten intolerance or coeliac disease

If gluten intolerance or coeliac disease shapes your daily food choices, you can still boost your gut microbiome through non-wheat-based prebiotic fibres, including many fruits, vegetables and legumes. If you choose to take a prebiotic supplement, always check the ingredients are not gluten based.

Accredited Practicing Dietitian and Accredited Nutritionist Kelli Beardsmore says,

“In general, most Australians do not consume enough fibre daily, and by association, prebiotic intake may also be low for these Australians. The recommended daily fibre intake is 30g for men and 25g for women, but it’s not just the amount of fibre; variety also counts. So, try to eat a variety of fibre-rich foods across all the food groups.

Fibre and water go hand in hand. When increasing fibre either by food choices or supplements, it is also essential to increase water intake. This aids digestion and ensures all the nutrients, minerals and vitamins can be fully accessed when metabolised by our gut microbiome”.

water, prebiotics act, digestive tract, beneficial microbes,
If you are experiencing a functional gut disease, living with SIBO, or following a FODMAP diet, chat with your Accredited Dietitian or healthcare professional about the best time to introduce prebiotics (and fibre) into your diet.

Are you interested in addressing your gut microbiome with personalised prebiotic dietary supplements?

Start with the Vidality gut microbiome test, and our pharmacists will compound a personalised blend of prebiotics based on your insights!


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Oniszczuk, Anna et al. “Role of Gut Microbiota, Probiotics and Prebiotics in the Cardiovascular Diseases.” Molecules (Basel, Switzerland) vol. 26,4 1172. 22 Feb. 2021, doi:10.3390/molecules26041172

Davani-Davari, Dorna et al. “Prebiotics: Definition, Types, Sources, Mechanisms, and Clinical Applications.” Foods (Basel, Switzerland) vol. 8,3 92. 9 Mar. 2019, doi:10.3390/foods8030092

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Manzione, Maria Giulia et al. “Phytochemical and pharmacological properties of asperuloside, a systematic review.” European journal of pharmacology vol. 883 (2020): 173344. doi:10.1016/j.ejphar.2020.173344

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