Fibre, fermentation, FODMAPs and flatulence

17th February 2023

Fibre is important for our health, as well as that of our microbiome. Gut microbe fermentation of fibre that reaches the colon releases beneficial compounds, but also gases. And for some, that gas can cause serious discomfort. Is there a way to endure everyone can reap the benefits of fibre?

What is fermentation?

Fermentation is the breakdown of complex carbohydrates by bacteria and other microbes to release energy. In the gut, this mainly happens in the colon, or large intestine. Here, different bacterial species within the microbiome ferment fibre and other complex carbohydrates that have survived digestion in the small intestine.

Why is gut microbiome fermentation important?

Fermentation provides the energy that bacteria need to survive and thrive, so providing plenty of fibre in the diet helps maintain a healthy microbiome. Fermentation also releases compounds called short chain fatty acids that have a range of benefits for gut health, and the health of other bodily systems.

Gut microbe fermentation and gas

As a by-product of this fermentation, gases are produced. These gases are eventually expelled from the body as flatulence. For some people, the production of gases in the colon can be uncomfortable, or cause bloating. For people with conditions such as Inflammatory Bowel Disease (IBD) or Irritable Bowel Syndrome (IBS) it can be a more serious problem, causing pain and exacerbating damage to the gut lining.

FODMAP diets

People with conditions like IBS may, under the supervision of a dietician, follow a low FODMAP diet that minimise fermentable carbohydrates and replace them with tolerable alternatives. FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols and different people have different sensitivities to each of these type of carbohydrate. After a period of cutting out all high FODMAP foods, small amounts from different categories may be added back to see what an individual can tolerate. So it’s important that a FODMAP diet is only started after consulting with your GP and under the supervision of a dietician. They are challenging to follow and risk introducing deficiencies in other key nutrients. And, with less fibre passing to the gut, there’s less chance of the microbiome supplying beneficial short chain fatty acids.

Fibre’s benefits without the discomfort?

3 million people in the UK are thought to have IBS, and with no known cure there’s been an effort to help them maintain optimum healthy diets that also control symptoms. Researchers at the Quadram Institute and University of Nottingham have been studying the properties of a type of dietary fibre called psyllium. This is derived from Plantago ovata plant seeds and is used as a thickener in foods and as a dietary supplement.

In a study recently published in the journal Food Hydrocolloids Dr Hannah Harris and Dr Fred Warren and colleagues from the Quadram Institute and University of Nottingham uncovered more detail about how psyllium is fermented.

Psyllium forms a viscous gel called mucilage, and they previously showed that there are several parts within the gel, which can be separated and differ in their physical properties. The team used a model of the colon seeded with faecal bacteria to understand how these different forms are fermented by microbes in the colon.

four square microscopy images of gut microbe fermentation side by side under 0,6, 24 and 72 hour labels. 0 hour is mostly orangewith patches of yellow, 6 and 24 are dull green, 72 hour image is orange surrounded with bright green/cyan

Microscopy images of gut microbe fermentation of psyllium fibre and the bacterial interactions over time. Bacteria show in differnt colours: Bacteroidetes (Cyan), Lactobacilli (orange) sand Bifidobacteria (yellow). From

They found that during fermentation the physical properties of psyllium determine gas production, but the chemical properties are behind short chain fatty acid production.

This finding opens up the opportunities to selectively breed plants or hone production methods that deliver new optimised forms of psyllium with all the health benefits of dietary fibre, but that reduce gastric discomfort.

Dr Hannah Harris said “These results are exciting, and we hope to investigate how these different properties of the psyllium influence the gut microbiota. Our data suggest that there is potential for individuals who experience gastric discomfort to have the advantages of consuming fibre without any negative effects.”

Reference: The impact of psyllium gelation behaviour on in vitro colonic fermentation properties, Hannah C. Harris, Noelia Pereira, Todor Koev , Yaroslav Z. Khimyak , Gleb E. Yakubov, Frederick J. Warren, Food Hydrocolloids DOI: 10.1016/j.foodhyd.2023.108543

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Fred Warren

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