Prebiotics and fiber: the unsung heroes of digestive health

Most of us are very familiar with probiotics and the health benefits these can bring to our gut microbiome, the collective of bacteria in our gastrointestinal tract. 

Probiotics are live microbes that, when consumed, help restore and maintain a healthy balance of good and bad bacteria in the gut. 

However, another nutrient that is under the radar but also essential to the balance of the gut microbiome is prebiotics. The name prebiotics means it is often confused with probiotics. 

The British Dietetic Foundation explains that prebiotics are a source of fuel for probiotics, helping probiotics to survive and produce good bacteria for the gut.

Monash University explains that prebiotics are dietary fibre, though not all fibres are prebiotic. Our bodies can’t digest prebiotics, but the beneficial microbes in our gut can. 

One 2019 review article in the Foods Journal explains that to be classified as a prebiotic, the fibre must pass through the GI tract undigested and to the large intestine. Once there, the prebiotics are selectively targeted by the gut’s microorganisms, which metabolise and ferment the prebiotics, stimulating the growth and activity of ‘good’ bacteria. The Foods Journal article explains that the fermenting process also produces short-chain fatty acids (SCFAs), which can have multiple positive effects on the body and health. 

In this way, prebiotics and probiotics work together to contribute to maintaining a healthy environment of beneficial flora in the gut, which is now well-recognised for its role in supporting immune, digestive, and mental health. 

According to the Dietitians Association of Australia (DAA), fibre plays a key role in gut health. The DAA also adds that a more diverse gut microbiome is thought to be most beneficial for overall health.

To boost the diversity of your microbiota, the International Scientific Association for Probiotics and Prebiotics (ISAAP) explains that the best way is to consume a diverse, fibre-rich diet that provides your gut with a wide variety of foods for many different species of bacteria.

Dietary fibre, as described by Monash University, is a natural prebiotic that passes through the gastrointestinal tract undigested, stimulating the growth and activity of good bacteria.

There are two types of fibre, both with different roles. 

Insoluble fibre does not dissolve in water but instead absorbs water to help soften the contents of our bowels, as Nutrition Australia states. This helps speed up food through the digestive system, promoting regular bowel movements. 

This type of fibre is found in wholegrain cereals and breads, nuts, seeds, and the skin of fruit and vegetables.

Soluble Fibre dissolves in water, forming a gel-like substance in the gut. Some types help slow down food passage through the gastrointestinal tract. This helps you to feel fuller, according to Nutrition Australia.

It is found mainly in plant foods such as fruit and vegetables, legumes, and barley.  

The British Dietetic Foundation explains that resistant starch (RS) is a soluble fibre that is highly fermentable in the gut. Good bacteria break it down to produce beneficial short-chain fatty acids (SCFAs). 

Resistant starch is present in bananas, grains, potatoes, and pulses.

The Baker Heart and Diabetes Institute advises introducing fibre slowly, as a sudden large increase can cause gas and bloating. 

According to Nutrition Australia, adult males require 30g per day, while females require 25g per day.

According to Monash University, foods that contain fibre with high prebiotic activity include inulin, fructooligosaccharides (fructans, FOS), and galactooligosaccharides.

They are often found in high-fibre foods.

Examples of such foods are below: 

Vegetables: Spinach, artichokes, boiled potatoes, as the starch is more resistant to digestion, asparagus, onion, chicory, garlic, leek, shallots, and spring onion

Legumes: Chickpeas, lentils, red kidney beans, baked beans, soybeans

Fruit: Berries, bananas that are less ripe, nectarines, watermelon, pomegranate, white peaches

Bread and cereals:  Cereal products such as oats and wheat bran, wheat and rye bread, rye crackers, pasta and couscous

Nuts and seeds: Flaxseeds, chia seeds, cashews, pistachio nuts

Human breast milk  also contains prebiotics

It’s important to gradually increase the amount of prebiotic foods you consume rather than eat a whole lot at once because they can produce gas, potentially making you feel bloated. 

Prebiotics are also available in supplement form. 

You most likely won’t see the word ‘prebiotic’ on the label. The ISAAP suggests instead looking in the ingredients list for galactooligosaccharides (GOS), fructooligosaccharides (FOS), oligofructose (OF), chicory fibre, or inulin. The Association recommends consuming at least 5 grams of prebiotics daily for improved gut health.

The Cleveland Clinic notes that it’s best to take prebiotics during the day as this is when the microorganisms are more active.

A 2020 research paper published in The American Journal of Lifestyle Medicine discusses how much of the data shows health benefits are associated with dietary fibre rather than those in supplements, so a food-first approach should be taken to achieve such benefits.

The research paper also notes that fibre supplements have demonstrated health benefits, such as including improved regularity. 

If you feel you may need extra support through fibre supplements, speak to your doctor first. Your doctor may also recommend you take a supplement for gut symptoms you may be experiencing. Supplements come in powder, capsules, and even gummies, and common ones include psyllium and inulin fibre.

Your healthcare provider can recommend the best one suited to your health situation.