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Study · Nature · 2022Conflicts declared

Inulin fibre, gut bacteria and type 2 inflammation in mice

Arifuzzaman M, Won TH, Li TT, et al · Free full text

What it found

Inulin fibre raised certain bile acids made by gut bacteria and increased a type of inflammation in the gut and lungs of mice.

The same bile acid also activated immune cells taken from people in lab tests.

What they found

Animal and lab studies

Gut bacteria shifted

After 2 weeks on the inulin diet, mice had more Bacteroidetes bacteria and fewer Firmicutes in their faeces compared with control mice. The authors note this shift matches patterns seen in human studies.

Bile acids rose in blood

Blood levels of several bile acids went up in mice eating inulin, especially cholic acid. Faecal levels of some other bile acids went down, suggesting more were being reabsorbed into the body.

More eosinophils appeared

Mice fed inulin had significantly more eosinophils, a type of inflammatory white blood cell, in their colons within one week. This increase stayed high beyond 2 months and was also found in their lungs.

Gut bacteria were required

Inulin did not raise eosinophils in germ-free mice that lacked gut bacteria. When germ-free mice received gut bacteria from healthy people, inulin again raised bile acid levels and triggered the inflammatory response.

Allergen reactions worsened

Mice fed inulin had stronger lung inflammation when exposed to papain, an enzyme used in food processing, or to house dust mite allergen. Inulin-fed mice infected with a parasitic worm also cleared the worms faster than control mice.

Studies in people and animals

Cholic acid triggered inflammation

Giving cholic acid alone to mice produced the same rise in eosinophils as the inulin diet. When this bile acid was added to human immune cells in lab dishes, it also increased the number of cells making an inflammatory signal called IL-5.

What the authors conclude

  • They conclude that inulin fibre changes gut bacteria in a way that raises cholic acid levels and drives type 2 inflammation in the gut and lungs.
  • They suggest this pathway could help explain how diet influences allergic responses and defence against parasites.
  • The authors propose that the overall effect of eating inulin depends on a balance between different chemicals made by gut bacteria.

How it was done

Scientists know that dietary fibres change gut bacteria and the chemicals those bacteria make, but they do not fully understand how different fibres affect the immune system. They wanted to map out exactly what inulin does to gut bacteria, their chemical outputs and the resulting immune responses.

Mice were fed either a normal diet or a high-fibre diet containing 26% inulin for 2 weeks. The researchers then measured changes in gut bacteria, blood chemicals and immune cells in the gut and lungs. Some experiments used germ-free mice given human gut bacteria, and some tested mouse and human immune cells in the lab.

What it can’t tell you

  • These findings come mostly from mice, so they cannot show exactly what happens in people who eat inulin.
  • The only test in human material involved immune cells in a dish, which may not reflect whole-body effects.
  • The study used a diet of 26% inulin, which is much higher than typical amounts found in everyday foods.

The paper

Title
Inulin fibre promotes microbiota-derived bile acids and type 2 inflammation
Type
Study
Evidence
Studies in people · animals · lab
Summarised from
Full text
Cite
Arifuzzaman M, Won TH, Li TT, et al (2022). Inulin fibre promotes microbiota-derived bile acids and type 2 inflammation. Nature. doi:10.1038/s41586-022-05380-yFree full textPubMed 36323778DOI

Summary written 1 Oct 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error