Dietary fibre may protect against asthma

Posted by AFN Staff Writers on 22nd January 2014
Dietary fibre, such as that found in vegetables, may help asthma sufferers

The ‘Western’ diet may have more to do with the asthma epidemic than has been assumed so far because developing asthma is related to the amount of fruit and vegetables consumed, according to new research from the Swiss National Science Foundation.

The research, undertaken by Dr Benjamin Marsland and colleagues at Lausanne University Hospital (CHUV), showed in experiments with mice that the lack of fermentable fibres in the diet paved the way for allergic inflammatory reactions in the lungs. Gut bacteria ferment the dietary fibres contained in them, and fatty acids enter the blood as a result, influencing the immune response in the lungs.

Researchers said that 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 even smaller role in people’s diets. The researchers said their results suggest that these two developments are not merely simultaneous, they are also causally linked.

Influence extends to lungs

Researchers have already known for some time that the microbial diversity in the gut when digesting and fermenting fibres plays a significant role in intestinal cancer.

“We are now showing for the first time that the influence of gut bacteria extends much further, namely up to the lungs,” said Dr Marsland.

Study method

The research team either put mice on a standard diet with four per cent fermentable fibres or gave them a low-fibre food with just 0.3 per cent fermentable fibres. The researchers said the low-fibre food was largely comparable to the ‘Western’ diet, which on average contains less than 0.6 per cent fibre.

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 likewise showed that these dietary fibres had a “protective” influence.

This protection was the result of a multi-level reaction chain, according to the researchers. 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.

Another reason why fruit and vegetables are good for the body

Dr Marsland said 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. But the researchers said many questions still remain unanswered.

“We plan to conduct clinical studies to find out how a diet enriched with fermentable fibres affects allergies and inflammations,” Dr Marsland said.

But the researchers said it is already sufficiently clear that this is another reason to eat more fruit and vegetables.