Gut fermentation of dietary fibres: implications for health


Almost two-thirds of Australian adults and a third of Australian children are either overweight or obese.1 Globally, there is an epidemic of obesity, along with related chronic diseases including type 2 diabetes and cardiovascular disease.2 What role does dietary fibre (DF) play?

Studies have demonstrated a link between low levels of DF and the occurrence of these diseases.2 DFs consist of edible plant parts that resist digestion and absorption in the small intestine and undergo complete or partial fermentation in the colon.

Often considered a single entity within nutritional guidelines, DF is a complex group of substances, including nonstarch polysaccharides, resistant starch, cellulose and hemicellulose, oligosaccharides, pectins, gums, lignin and waxes.

One of the main benefits of DF is its fermentability, which affects microbial diversity and function within the gastrointestinal tract (GIT), as well as the by-products of the fermentation process.2

Studies on DFs have examined purified ingredients extracted from plants. However, the validity of this is questioned in terms of nutritional value, with evidence to suggest that it is the actual complexity of DF that affects the complexity of the GIT microbiota.2

In a study published in the International Journal of Molecular Sciences, researchers looked at what we know about different forms of DF, as well as how the GIT microbiota responds to these compounds.

By reviewing the literature comparing the results of fermentation of purified DF substrates with whole plant foods, the authors found strong indications that the more complex and varied the diet (and its ingredients), the more complex and varied the GIT microbiota is likely to be.

‘Intuitively, this makes sense, as many bacterial species have the enzymes required for the breakdown of very specific molecules,’ the authors stated.

‘Hence, the more varied the molecules present, the greater variety of bacteria required to break them down.’

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  1. Australian Institute of Health and Welfare. A picture of overweight and obesity in Australia 2017. Canberra: AIHW; 2017. At:
  2. Williams BA, Grant LJ, Gidley MJ, et al. Gut fermentation of dietary fibres: physico-chemistry of plant cell walls and implications for health. Int J Mol Sci. 2017;18(10):2203.