Fibre is more than just roughage: the role of fermentable fibres (prebiotic fibres, including resistant starch) on gut health

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CPD hours are applicable for Australian and New Zealand dietitians.

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Wholegrains contain complex carbohydrates – starch and dietary fibre – which benefit human health through various mechanisms including faecal bulking and gut fermentation. Dietary fibre consists principally of non-starch polysaccharides (NSP) which cannot be digested in the small intestine and passes into the large bowel. Modern refined foods are low in fibre and population studies show that greater fibre consumption lowers diet-related disease risk. However, data are inconsistent and in the Australia, where fibre consumption is moderate-to-acceptable in relation to dietary fibre intake recommendations, colorectal cancer remains high.

In the large bowel, resistant starch (RS) is fermented to short-chain-fatty-acids (SCFAs) by the microbiata. The main SCFAs are acetate, propionate and butyrate. SCFA improve gut health via various mechanisms, including decreasing colonic pH and providing substrate to colonic cells. Butyrate is particularly important for large bowel integrity. RS levels are very low in western diets, which leaves the large bowel microbiota ‘hungry’ for fermentable fibre. It is suggested that diet-related bowel diseases may be due to SCFA deficiency, stemming largely from inadequate fermentable fibre and RS intakes. Of course, increasing whole grain intake has been shown to be protective, across a range of chronic lifestyle mediated disease conditions.

Dietary prebiotics are defined as “selectively fermented ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health”. Examples of foods rich in dietary prebiotic fibre include Barley+, legumes and lentils, sorghum, onions, garlic, leek and asparagus. Dietary prebiotics provide substrate for the gut microbiota and subsequently can change the composition and activity of resident gut microbiota. This in turn appears to have knock on ‘gut health’ benefits.

Our webinar objectives are: 

1. Define and discuss a variety of fibre types (fermentable fibres like resistant starch), as distinguished from insoluble fibres (roughage-type-fibre) and soluble fibres

  • List food sources of the various fibre types
  • Understand differences in metabolism of highly refined processed CHO versus minimally refined /processed CHO
  • Understand the major functions of Fermentable Fibres, Insoluble Fibres and Poorly Fermented Soluble Fibers (e.g. beta-glucan, psyllium)
  • Note differences in metabolism/excretion of the various fibre types

2. Discuss function & relative importance of the diverse fibre types, in relation to:

  • Immune system & gut health/CRC risk reduction
  • Weight, mental health/mood, etc.


Participants will also be able to:

  • Apply research/evidence-based findings in the area to improve practice, service delivery, and health and nutrition of clients; and
  • Integrate new knowledge and skills obtained during this webinar into practice.

About the presenter:

Dr Joanna McMillan originally hails from Scotland, and came to Australia in 1999, where she won a scholarship to complete her PhD in Nutritional Science at The University of Sydney. As a dietitian and former fitness instructor, she is driven by a passion to promote the influence that diet and lifestyle have on our health and wellbeing. She is a published author, an international presenter and a regular on our TV screens, including being the host for the Gut Revolution series on ABC Catalyst. Joanna is a nutrition advisor to Freedom Foods.

This webinar is supported by 


Presented By
Dr Joanna McMillan
Professional Development
Duration1 hour