Fibre & Prebiotics for Gut Health: Feeding the Gut Bacteria

Gut health has become a ‘health trend’ in the past few years. More and more people are interested in maintaining a healthy gut, and for good reason! Our digestive tract not only helps with the breakdown of food and absorption of nutrients, but research has also shown a link with our mental health.

Last week I shared on the importance of the microbiota or gut bacteria in helping reduce our risk for bowel cancer. One of the key ways identified was to increase fibre in the diet. Today I thought I’d discuss a bit more about WHY fibre is so important, the different types of fibre and how we can include these in our diet.

First off, let’s clarify something. We always use ‘fibre’ as an umbrella term, but did you know that there are actually 3 different types of fibre?

The reason fibre is so important for gut health is because they act as a prebiotic. Now, that word sounds familiar. You may have been hearing it a lot lately. Not to be confused with probiotics which are the actual LIVE bacteria, prebiotics are FOOD for the bacteria. 

Many fibre foods act as prebiotics because of the way they are digested. Put simply, some fibre foods aren’t completely broken down in the small intestine, causing them to travel into the large intestine where they ferment into short chain fatty acids (SCFA).

At this stage, it’s important to remember 2 things:

  • Not every fibre is a prebiotic
  • Too much fermentation can cause excess gas and symptoms like bloating and abdominal discomfort

Whilst fermentation in the gut sounds kind of gross and too much can cause issues, some fermentation is important. The SCFAs created during fermentation acts as fuel, feeding and encouraging the growth of good gut bacteria. This then affects both the composition and activity of the microbiota (gut bacteria). Butyrate, a type of SCFA, is particularly important for cells lining the large intestine. 

It’s important to remember 2 things: not every fibre is a prebiotic, and too much fermentation can cause excess gas and symptoms like bloating and abdominal discomfort.

So which types of fibre are more fermentable and a better prebiotic for gut bacteria?

Soluble fibre and resistant starch are the most fermentable types of fibre, and therefore act as better prebiotics. Resistant starch (RS), in particular, is one of the most important. It is highly fermentable, and several studies have found higher levels of specific bacteria when consuming a higher RS diet. These bacteria include Bifidobacterium, Bacteroides, Lactobacillus, and Eubacterium, all of which are linked to reduced inflammation in the colon and improved immune function. RS has also been researched in diabetes and lipid metabolism, comparing the effects of a diet high in RS and low RS diet. If you’re interested in learning more about the science behind resistant starch, CSIRO have a great video on their site.

Contrastingly, if we’re just talking about fermentability, insoluble fibre has the least benefit as a prebiotic. However, insoluble fibre has another really important role – it helps to carry resistant starch all the way down the digestive tract. Without this transportation process, the fermentation of resistant starch would happen a lot higher up the digestive tract, causing more gas and potentially abdominal discomfort.

Based on the above, the moral of the story is that all three types of fibre are important to feed the gut bacteria.

So how can we include all these types of fibre in our diet? Which foods contain what?

Hopefully the infographic above helps give you a visual idea of what types of foods contain which types of fibres. Next week I will be sharing more on fibre, including practical tips on how to include more in your diet, and how much to aim for every day. Be sure to check back then!

*Disclaimer: The information above is intended to be used as a guide only and may not be applicable to everyone. Each individual will have unique requirements depending on their own health conditions. Please consult your doctor or health professional if unsure.

References & Further Reading

CSIRO. (2019). Nutrition and gut health – Resistant starch. Retrieved from CSIRO, https://www.csiro.au/en/Research/BF/Areas/Nutrition-and-health/Nutrition-and-gut-health/Resistant-starch

Hermann, E., Young, W., Rosendale, D., Conrad, R., Riedel, C., & Egert, M. (2017). Determination of Resistant Starch Assimilating Bacteria in Fecal Samples of Mice by In victor RNA-Based Stable Isotope Probing.Frontiers in Microbiology. 8:1331. Accessed from https://www.frontiersin.org/articles/10.3389/fmicb.2017.01331/full

Maier, T. et al. (2017). Impact of dietary resistant starch on the human gut microbiome, metaproteome, and metabolome. American Society for Microbiology. 8:e01343-17. Accessed from https://mbio.asm.org/content/8/5/e01343-17/article-info

Silvi, S., Rumney, C., Cresci, A., & Rowland, I. (2001). Resistant starch modifies gut microflora and microbial metabolism in human flora-associated rats inoculated with faeces from Italian and UK donors. Journal of Applied Microbiology. 86(3). Accessed from https://onlinelibrary.wiley.com/doi/full/10.1046/j.1365-2672.1999.00696.x