Dietary fibres protect the lungs from asthma

10 January 2014

Researchers at Lausanne University Hospital (CHUV) have shown that fermentable fibres present in fruit and vegetables start a chain reaction that enables the body to protect the lungs from the inflammatory response in asthma.

 The fermentable fibres are transformed in the gut into short-chain fatty acids which enter the bloodstream and affect production of immune cells in the bone marrow. These immune cells in turn protect the lungs from asthma.

In the West, an increasing number of people have developed allergic asthma in the past fifty years. But dietary habits have also changed during the same period: fruit and vegetables are playing an ever smaller role in people's diets. It has already been known for some time that the microbial diversity in the gut when digesting and fermenting fibres plays a significant role in preventing intestinal cancer. Now these new results suggest that asthma and lack of fruit and vegetables in the diet are also causally linked. So the western diet probably has more to do with the asthma epidemic than has been assumed so far.

In the study, the researchers either put mice on a standard diet with 4% fermentable fibres or gave them low-fibre food with merely 0.3% fermentable fibres. This low-fibre food is largely comparable to the Western diet, which contains no more than 0.6% fibres on average.

When the researchers exposed the mice to an extract of house dust mites, the mice with the low-fibre food developed a stronger allergic reaction with much more mucus in the lungs than the mice with the standard diet. Conversely, a comparison between mice on a standard diet and mice who received food enriched with fermentable fibres showed that these dietary fibres have a protective influence.

Protection mechanism

This protection is the result of a multi-level reaction chain. First the fibres reach the intestine, where they are fermented by bacteria and transformed into short-chain fatty acids. These acids then enter the bloodstream and influence the development of immune cells in the bone marrow. Attracted by the extract of house dust mites, these immune cells wander into the lungs, where they eventually trigger a weaker allergic response.

Lead researcher Benjamin Marsland thinks that the results obtained by his group are clinically relevant not only because the share of plant fibres in Western diets is comparable to the low-fibre food of the mice, but also because the examined aspects of the immune system are virtually indistinguishable in mice and humans.

Many questions still remain unanswered so the team plans to conduct clinical studies to find out how a diet enriched with fermentable fibres affects allergies and inflammations. It is already sufficiently clear, however, that here is another reason to eat more fruit and vegetables.

Reference

Trompette A, et al. Gut microbiota metabolism of dietary fiber influences allergic airway disease and hematopoiesis through GPR41. Nature Medicine. 2014. doi: 10.1038/nm.3444