Dietary fibres make our gut bacteria behave healthily

We get healthy dietary fibres from consuming fruits, vegetables, and whole grains. But why are the fibres so good for us? A team of researchers has discovered that dietary fibres play a crucial role in determining the balance between the production of healthy and harmful substances by influencing the behaviour of bacteria in the colon.

Picture: Colourbox

Understanding the behaviour of gut bacteria

It is well-known that dietary fibres can alter the composition and quantities of bacteria in our gut microbiome. However, looking merely at composition and abundance of gut microbial species will not tell us much about their impact on our health.

“The gut microbiome research field has had a strong focus on assessing effects e.g. of diet on the quantity of potentially good or bad gut bacteria, but often neglect that diet can regulate the gut bacteria’s activity without necessarily making major changes in the quantity of bacterial species in the colon,” says an associate professor at DTU National Food Institute, Martin Frederik Laursen.

So, dietary fibres not only help modify the types of bacteria in the gut, leading to a healthier composition, they also influence the behaviour of gut bacteria in ways that promote health.

“As a research community we need to change focus from viewing gut bacteria and their abundances strictly as either good or bad – to instead understand how we make our gut bacteria behave good or bad.” says Martin Frederik Laursen.

This understanding can help scientists develop better dietary recommendations that keep our gut healthy and prevent diseases. 

The essential amino acid tryptophan is converted in the large intestine into either beneficial or harmful substances. The research shows that tryptophan contributes to the production of the healthy substances Indole lactic acid (ILA) and Indole propionic acid (IPA) when we consume sufficient amounts of dietary fibre. However, if we do not get enough dietary fibre, tryptophan will be converted into the substance indole, which is associated with adverse health effects. This figure was created with BioRender( by Martin Frederik Laursen


Essential amino acids, such as tryptophan, must be obtained through the diet since the body cannot synthesize them.

Protein-rich foods serve as sources of tryptophan. Examples include chicken, turkey, salmon, tuna, eggs, milk, cheese, yogurt, legumes, nuts, and seeds.

Dietary fibres are present in fruits, vegetables, and whole grains. 

Original study title: “Dietary fibre directs microbial tryptophan metabolism via metabolic interactions in the gut microbiota

The research is funded by the Novo Nordisk Foundation project PRIMA, led by Professor Tine Rask Licht at DTU National Food Institute. Grant no: NNF19OC0056246

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Learn more about the research group for Gut, Microbes and Health at DTU National Food Institute’s website.