Could different types of fibre have unique effects on our gut bacteria?

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By The Gut Health Doctor Team

Dr Megan Rossi in a lab looking through a microscope

You’ll all know by now that fibre is good for us. Fibre feeds our gut bacteria and keeps them thriving, so they can keep looking after us in so many ways.


All our plant-based foods provide a diverse variety of fibre and there are thought to be over 100 different types – but could different fibres have unique effects on our GM (gut microbiota) and influence the chemicals they produce in our body? A new study suggests they might!


In the new study, 40 healthy individuals, who normally ate the UK average of around 18g of fibre daily, were given different types of resistant starch for 4 weeks: corn, potato, tapioca or a placebo (digestible corn starch). Each week, the participants increased their doses of fibre (on top of their 18g a day already), starting with an extra 10g per day in week 1, increasing to 20g, 35g and finally 50g per day in week 4. The activity of their GM, as well as gut symptoms, were measured at the end of each week.


What did they find?

Having 20g a day of the same type of fibre (corn and tapioca) actually led to a decrease in GM diversity – and remember, having more diversity is linked with better the health outcomes. This is thought to be because having large amounts of just one kind would favour one type of bacteria over others. So, relying on just one source for our daily fibre intake may not be such a good idea for our GM.

The non-fermented fibres (potato and the placebo) didn’t have this diversity-reducing effect, indicating that potato fibre doesn’t have the same influence on our GM as other prebiotic fibres.

It’s worth mixing up the menu as much as possible. For example, if you’re planning to have wholewheat pasta for lunch, go for a different starchy carb for breakfast, such as oats or buckwheat, then choose rice or quinoa for dinner.


Was there any impact on the products produced?

You see, each type of dietary fibre has a different structure and our microbes each favour different fibres – that’s why the variety is important, so we’re feeding a whole range of microbes. And when our GM ferments or ‘eats’ these fibres, they produce short-chain fatty acids (SCFAs), which are known to be beneficial for our health.

When looking at the individual effect on the gut bacteria, corn and tapioca not only influenced the types of bacteria they increased, but they also had very specific effects on what SCFAs the bacteria produced (at 35g a day, corn increased butyrate and tapioca increased propionate). Potato and the placebo didn’t have any impact. In practice, while it’s interesting to see, these changes didn’t seem to mean much for our overall health.


Full disclosure!

Now, this is a small study with only 10 participants per group and the authors themselves did caution against oversimplifying the results. We’ve got a long way to go before we can start recommending specific fibres for certain types of microbes – it’s highly individualised after all. But it does suggest there might be an opportunity in the future for targeted alterations to our GM. Watch this space…


Key take-home:

When it comes to fibre, variety is key! Focusing on just one type could negatively impact our GM by reducing the diversity. Think about incorporating all six plant-based food groups: fruits, vegetables, wholegrains, legumes (beans and pulses), nuts and seeds. Tinned, fresh and frozen all count. Each different type feeds different gut bacteria and has different effects on their activity, and we want a diversely skilled team of microbes for better health outcomes.


Gut Glossary

  • GM = gut microbiota, the trillions of microbes living within us

  • SCFAS = short-chain fatty acids are produced by our GM when they ferment or ‘eat’ dietary fibre. They’re considered beneficial to our health for a number of reasons, including links to maintaining our gut lining, modulating our immune system and reducing inflammation.

  • Resistant starch = a type of fibre that quite literally ‘resists’ digestion in your small intestine, making its way down to the large intestine where your GM love to feast on it and produce beneficial compounds (short-chain fatty acids, or SCFAs)


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