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,

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

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

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

Microbiota (Gut Bacteria) and Bowel Cancer: what’s the link and how can we reduce our risk?

Just in time for Bowel Cancer Awareness month, I thought I would start off my first blog series on gut health – specifically, the gut microbiome (or gut bacteria).

Did you know that bowel cancer is the second most common type of cancer in Australia? Of all diagnosed cases, 30% of people typically have a family history of the condition. However, apart from genetic factors, recent research has shown that certain microbiota (including in the mouth) may also impact our risk for bowel cancer.

Microbiota are the bacteria living in our digestive tract, from the mouth right down to the rectum. They help to maintain the ‘environment’ in our gut, and humans have an estimated 100 trillion bacteria in the intestine. Different types or amounts of microbiome can cause an imbalanced ‘environment’, and can not only impair digestive function, but may also cause symptoms like constipation, diarrhoea and bloating.

Microbiota help to maintain the ‘environment’ in our gut’, and humans have an estimated 100 trillion bacteria in the intestine.

While we may be born with certain types of microbiome (dependent on genetics and parents’ lifestyle at conception), these gut bacteria regularly change. Diet is something that can greatly influence the types and amounts of bacteria in your gut.

For example, in a study comparing the diets of European children and rural African children, key differences were found with a greater variety of bacteria in the rural African children. These children had a higher biodiversity of gut bacteria, including those related to anti-inflammation and protecting against bowel diseases.

Another review by Yang & Yu compiled the results from several different human and animal studies and found that fibre, protein and fat intake were the main influencers to gut microbiota. The key points were:

  • The fermentation of fibre in the large intestine produces short-chain fatty acids (SCFAs), particularly butyrate. This acts as ‘food’ for the cells in the colon and promotes anti-inflammatory actions.
  • High intakes of animal protein did not change the variety of microbiota but did cause protein fermentation and bile acid deconjugation, which in turn increased inflammation of the colon.
  • Diets high in fat, particularly from processed meats and red meat, increased the release of bile acids, which damaged the lining of the intestines.
  • There were conflicting studies on whether processed meat and red meat consumption caused increased risk for developing bowel cancer; however, most of the current evidence suggests that there is an increased risk.

So, it seems like the biodiversity or variety of microbiota is important in helping to reduce the risk of bowel cancer, as is reducing inflammation in the colon. What things can we do to improve the amount and variety of gut bacteria and reduce the risk of inflammation?

Two key methods stood out based on the above research:
  1. Increase fibre intake
  2. Decrease intake of processed and red meats

This post was a nerdy summary of the current scientific evidence in microbiome and bowel cancer. I hope my fellow science nerds enjoyed it. If that’s not you and you feel way in over your head, don’t stress! Over the next few weeks I will be sharing some more simple and practical tips, including how to take the above two methods on board. They will be actionable ways to help you eat your way to a healthier gut!

If you haven’t had enough of the science and still want to learn more, check out the further reading below!

腸道健康:人體消化道微生物(腸道細菌) 與腸癌


正巧本月份是腸癌關注月,我將會寫我第一篇網誌關於腸道健康,特別有關於人體消化道微生物(腸道細菌) 。






另外,Yang & Yu從許多以人類和動物的研究中收集了不同的結果,發現纖維,蛋白質和脂肪吸收是最主要影響腸道微生物的因素。重要理據包括:

  • 當纖維在大腸內發酵會生產短鏈脂肪酸(SCFAs),特別是丁酸酯(丁酸鹽)。這行為會給予大腸內的細胞足夠的營養和促進抗炎的功能。
  • 多吸收動物蛋白質不會改變微生物的多樣性,但會引致蛋白質發酵和膽汁酸早期解離,即是會增加大腸發炎的機會。
  • 當習慣進食一些高脂肪的食物,特別是經過處理的肉和紅肉,會增加膽汁酸的釋放溶量,這會損害大腸內壁。
  • 學術界在食用經過處理的肉和紅肉會否增加導致腸癌的風險存有分歧,然而,現時大多證據都偏向指出是會增加患癌風險


  • 增加進食纖維
  • 減少進食經過處理的肉類和紅肉

References & Further reading

Bowel Cancer Australia. (2017). About Bowel Cancer. Retrieved from Bowel Cancer Australia:

Dahmus, J., Kotler, D., Kastenberg, D., & Kistler, C. (2018). The gut microbiome and colorectal cancer: a review of bacterial pathogenesis. Journal of Gastrointestinal Oncology. 9(4):769-777. Accessed from

Filippo, C., Cavalieri, D., Di Paola, M., Ramazzotti, M., Poullet, J., Massart, S., Collini, S., Pieraccini, G., & Lionetti, P. (2010). Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa. Proceedings of the National Academy of Sciences of the United States of America.107(33):14691-14696. Accessed from

Flemer, B., Warren, R., Barret, M., Cisek, K., Das, A., Jeffery, I., Hurley, E., O’Riordain, M., Shanahan, F., & O’Toole, P. (2018). The oral microbiota in colorectal cancer is distinctive and predictive. Gut.67(8). Accessed from

Food and Mood Centre. (2016). Diet and the gut microbiota. Retrieved from

Yang, J., & Yu, J. (2018). The association of diet, gut microbiota and colorectal cancer: what we eat may imply what we get. Protein & Cell.9(5): 474-487. Accessed from