12 January - 20 June 2016

Gut microbes need their fibre otherwise they eat the colon lining

Consuming dietary fibre has been reported to have numerous health benefits, however there is little evidence as to the mechanism by which fibre deprivation impacts the gut microbiota and changes disease risk. A mouse study published in the journal Cell has sought to understand the mechanisms behind fibres health benefits.

Consuming dietary fibre has been reported to have numerous health benefits, however there is little evidence as to the mechanism by which fibre deprivation impacts the gut microbiota and changes disease risk.  A mouse study published in the journal Cell has sought to understand the mechanisms behind fibres health benefits.

The international team of researchers investigated the impact of fibre deprivation in mice who were bred to have no gut microbes. The mice received a transplant of 14 bacteria that normally grow in the human gut.  As Martens et al. knew the full genetic signature of each of the bacteria, they were able to monitor their activity and show how they evolved over time. 

The mice were housed in a special germ-free facility, allowing the scientists to study the bacteria present and active under different conditions and study the impact of diets with different fibre content, and with no fibre, on the gut microbiota.    The mice were infected with the bacterial strain, Citrobacter rodentium similar to Escherichia coli in humans.  Martens et al. investigated the impact of a diet containing 15% fibre, made from minimally processed grains and plants, a diet that lacked fibre and a diet rich in supplement-like prebiotic fibre and the interactions between the fibre, the gut microbiota, and the colonic mucus barrier, which acts as a defence. 

They report that when the 15% fibre diet was consumed, the mucus layer stayed thick and protected the mouse from infection. The mucus layers forms a physical barrier between the gut content and the gut lining.   However when the diet was substituted with no fibre, even for a few days, the gut microbes starting to consume the mucus layers, as it contains glycoproteins as a nutrient source.  After a few days the bacteria started to consume the colon wall. Martens et al. found that the diet high in prebiotic fibre, similar to that found in some processed foods and supplements, showed similar results to the diet that lacked fibre and together with dietary fibre deprivation and mucus eroding bacteria, caused greater epithelial access and lethal colitis by the mucosal pathogen.  The scientists also found the fibre-free diet caused the mice to show signs of illness and lose weight.

Martens et al. discovered that in the low fibre and no fibre conditions, the four bacteria strains that were promoted the most were producing enzymes that break down glycoproteins that make up the mucus layer. Using genetic information the team found more than 1600 different enzymes which were capable of degrading carbohydrates. Diet also affected the mixture of enzymes present with occasional fibre deprivation causing more mucus degrading enzymes. 

On examination of gut tissue Martens et al. found the fibre deprived diet caused the mice to have thinner or patchy mucus layers, and inflammation across a wider area.  Those that had received a high fibre diet before infection, showed some inflammation however this was across a smaller area.

In conclusion the team state that “your diet directly influences your microbiota, and from there it may influence the status of your gut’s mucus layer and tendency toward disease.  But it’s an open question of whether we can cure our cultural lack of fibre, with something more purified and easy to ingest than broccoli.”

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