In the past 50 years, as fruits and vegetables have featured less and less in the Western diet, rates of allergic asthma have gone up. Now a new study suggests these trends are not coincidental, but causally linked.
Funded by the Swiss National Science Foundation (SNSF), and led by Benjamin Marsland, an assistant professor at Lausanne University Hospital (CHUV) in Switzerland, researchers report their work in a recent online issue of Nature Medicine.
Using laboratory mice, they found that when gut bacteria digest dietary fiber, such as that contained in fruits and vegetables, they release fatty acids into the bloodstream, and these affect how the immune system behaves in the lungs.
The finding builds on knowledge that has been around for some time: that having a rich and diverse mix of microbes in the gut that digests and ferments fiber, helps prevent cancer of the intestines.
Prof. Marsland says:
"We are now showing for the first time that the influence of gut bacteria extends much further, namely up to the lungs."
For their study, he and his colleagues tested three groups of lab mice. They put one group on a low-fiber diet, comparable to a Western diet, averaging no more than 0.6% fiber, another group on a standard diet comprising 4% fermentable fiber, and the third group on a standard diet enriched with fermentable fibers.
To provoke an allergic response, the researchers exposed the mice to an extract of house dust mites.
Mice on low-fiber diet had stronger allergic reaction to dust mites
They found that the mice on the low-fiber diet had a much stronger allergic reaction - with more mucus in the lungs - than the mice on standard diet with more fiber.
And the mice on the enriched fiber diet showed an even stronger protective effect than the mice on the standard diet.
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