Writing in Nature Medicine, the team behind the mouse study noted that the past 50 years have seen an increasing prevalence of asthma in addition to changing dietary habits including a decreased intake of dietary fruit and vegetables. While these two trends have been shown to correlate for some time, there has been very little evidence to suggest a causal link between them, they added.
Led by Benjamin Marsland from Lausanne University Hospital (CHUV), Switzerland, the new study in mice, however, has begun to suggest a causal link - by demonstrating that altered intakes of fermentable fibres can lead to changes in the composition of the gut and lung microbiota, and that these alterations affect the severity of allergic reactions to dust mites.
"We are now showing for the first time that the influence of gut bacteria extends much further, namely up to the lungs," explained Marsland.
"Mice fed a high-fibre diet had increased circulating levels of SCFAs and were protected against allergic inflammation in the lung, whereas a low-fibre diet decreased levels of SCFAs and increased allergic airway disease," the researchers wrote.
Marsland and his team gave mice either a standard diet with 4% fermentable fibres or low-fibre food with just 0.3% fermentable fibres. This low-fibre diet is largely comparable to the Western diet, which contains no more than 0.6 percent fibres on average, the team noted.
The team then exposed the mice to an extract of house dust mites, finding that 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.
The protection against this allergic reaction in mice receiving the higher-fibre diet was found to be the result of a multi-level reaction chain, said Marsland.
"We found that dietary fermentable fibre content changed the composition of the gut and lung microbiota, in particular by altering the ratio of Firmicutes to Bacteroidetes," the team noted.
Marsland added that he believes 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.
"We plan to conduct clinical studies to find out how a diet enriched with fermentable fibres affects allergies and inflammations.," he added.
Source: Nature Medicine
Published online ahead of print, doi:10.1038/nm.3444
"Gut microbiota metabolism of dietary fiber influences allergic airway disease and hematopoiesis"
Authors: Aurélien Trompette, Eva S Gollwitzer, et al