Prebiotics: what are they and why are they important for gut health?

Author: Christine Stewart

29 June 2019 Nutrition
Prebiotic foods to improve gut health.

With the rising popularity of gut health and nutrition, everyone is talking about prebiotics. But what exactly are prebiotics? And why are they so important?

Prebiotics: a changing definition

Just like us, our gut bacteria require fuel sources to help keep them going. The fuel sources that specifically feed and nourish the health promoting bacteria are called prebiotics1.

The current definition of a prebiotic, according to the International Scientific Association for Probiotics and Prebiotics (ISAPP), is:

“A prebiotic is a substrate that is selectively utilised by host microorganisms conferring a health benefit”1

However, this current definition of a prebiotic is highly likely to change in the future. This is largely because the science on the microbiome—and prebiotics in general—is constantly evolving.

Understanding prebiotics further

Prebiotics are actually a relatively new concept and area of research.

The idea of prebiotics was first introduced by scientists around two decades ago2,3. Way back in 1995 (think when Braveheart was released), two scientists defined a prebiotic as a ‘non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon’3.

Sounds complex, but this original definition is not dissimilar to today’s definition. It tells us that there are parts of our food that are reserved for the bacteria that provide a benefit to our bodies. These non-digestible parts of our food (prebiotics) either encourage the growth of beneficial bacteria or increase their actions in our gut.

For your gut microbiome to flourish, you need to nourish it with the right types of prebiotics. Learn more about the types of prebiotics your microbiome may need.

Just as the science on the microbiome (community of microbes living in your gut) and prebiotics has evolved, so too has the definition, with several revisions and proposals occurring over the years4,5,6,7. Yet, despite the shifting complexities and evolving scientific discoveries surrounding prebiotics, some common features have remained.

What are the common features of a prebiotic?

To better understand what a prebiotic is, let’s unravel the current definition a little more. A substrate is a molecule that can be broken down into smaller parts with the use of enzymes which are a type of protein. A prebiotic:

Is resistant to human digestion4,5. It can’t be broken down by human enzymes so it travels through the small intestine before reaching the large intestine relatively untouched.

Can undergo fermentation by gut microbes4,5. Gut bacteria can break down resistant substrates by using their own unique enzymes8,9.

Selectively encourages the growth or beneficial action of health-promoting bacteria4,5. Prebiotic substrates once broken down, provide nutrients to the bacteria that provide a health benefit3.

So, are prebiotics the same as fibre?

No. Not all fibres are the same. Some fibres act as a prebiotic and selectively stimulate the growth and/or activity of beneficial bacteria whereas others, such as most insoluble fibres are less readily fermented by our gut microorganisms9,10 and act mostly as a bulking agent for stools. Nevertheless, it is still very important to consume adequate amounts of fibre in our diet. Most plant-based sources contain various types of beneficial fibres (prebiotic or not).

As the prebiotic definition can somewhat overlay that of dietary fibre, consumers should be aware that not all dietary fibres are necessarily prebiotics.

Which prebiotics should I eat to achieve a healthy gut?

The answer to this question is not simple. There are hundreds of different species of bacteria in our gut microbiome that can play a beneficial role and we all have different combinations of these. For example, two equally healthy people can have very different looking microbiomes.

This means that the prebiotics and other nutritional fuel sources required to support or promote a ‘healthy’ microbiome will differ from person to person.

The best tips to improve gut health is to encourage and nourish the growth of the health-promoting bacteria that have taken up residence within you. We do this by consuming adequate prebiotics so they can thrive deep within our gut.

With that in mind, if the beneficial bacteria in your gut were to ‘order in’, what would they choose from the menu? Here are some of the prebiotics (both established via studies and promising candidates) your beneficial bacteria might like to order:

Resistant oligosaccharides– Found in foods such as wheat, rye, onion and garlic.

Resistant Starch* – Found in green bananas, oats and cooked and cooled rice and potatoes.

Phytochemicals* – Generally found in many fruits, vegetables, wholegrains, nuts and legumes.

Non-starch polysaccharides* – Found in rye, wheat, barley, oats, apples and plums.

Feed your microbiome the rainbow

The more we learn about the gut microbiome, the more we understand how diverse this inner landscape is. To achieve and maintain a good level of diversity, we need to consume a wide range of prebiotics to feed and nourish the assortment of bacteria that have made our guts their home.

To do this, eat a variety of plant-based foods from across the rainbow, as this will provide the microbiome with an array of prebiotics.

However, if you’re looking for something more specific, the Microba Insight™ report provides an evidence-based list of foods that contain a variety of prebiotic substrates. Our test gives you a comprehensive look at the bacteria living in your gut and which ones need to be fed from a different menu.

Microbiome Prebiotics

Discover your microbiome’s ideal menu. Start your Microba Insight™ journey.


*The evidence (especially in humans) for some of these candidate prebiotics is not as advanced as the current evidence for the resistant oligosaccharides such as Inulin, FOS and GOS.

This microbiome test is not intended to be used to diagnose or treat medical conditions. A full disclaimer is available here.


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