A high fibre diet may help ward off asthma Special

Posted Jan 9, 2014 by Sherene Chen-See
We know that a diet high in fibre can help improve irritable bowel syndrome, Crohn's disease, and possibly colon cancer, but what about non-gastrointestinal conditions? In a new study, scientists have shown that fibre can help guard against asthma.
Naturally-occurring methanol is found in many of the fruits and vegetables we consume.
Naturally-occurring methanol is found in many of the fruits and vegetables we consume.
Ned Raggett
When we eat a fibre-rich diet, our intestinal bacteria helps us digest the fibre. Soluble fibre such as pectin, found in citrus fruits, pears, berries, apples, and onions, is taken by the microbes and fermented into fatty acids that interact with immune cells in a way that helps the body keep inflammation in the digestive system under control.
The effect of fibre beyond the digestive system is less clear. However, the fatty acids that are made in the digestive system can circulate through the bloodstream. Perhaps in the process, they can interact with immune cells throughout the body. We do know that asthma rates in the Western world have increased since the 1960s, while fibre consumption has gone down. Also, asthma is uncommon in areas of the world, such as parts of Africa, where a larger part of the diet is composed of fruits and vegetables, explains Science Now.
Immunologist Benjamin Marsland of the University of Lausanne, Switzerland, and his colleagues decided to test whether there is a link between fibre and asthma. First, they put a group of mice on a low-fibre diet. Two weeks later, they had the mice sniff a dust mite allergen (an asthma trigger). The mice experienced exaggerated asthma responses, including inflammation in the lungs and constricted airways.
They gave another group of mice a diet high in pectin for two weeks before giving them the dust mite allergen. These mice showed a reduced inflammatory response, says a report by the BBC. Their levels of immune cells called eosinophils, and of the antibody immunoglobulin E, which generally increase in asthma, were reduced by almost half, and they had less airway constriction.
"We were surprised that changing a single dietary component could alter the severity of allergic responses in mice, but did approach the study with the hypothesis that fibre would be beneficial," said Marsland in an interview with Digital Journal.
The results were reported in a recent online edition of Nature.
Marsland and his team analyzed the feces and blood of the mice and found that those who were given the high-pectin diet had twice the amount of bacteria that best produces anti-inflammatory fatty acids, compared to those mice who were given low-pectin diets.
To test whether the fatty acids were interacting with the immune system, the researchers then injected the mice with one of those anti-inflammatory fatty acids, propionate, After two weeks, these mice, when given the dust mite allergen, again showed reduced inflammatory markers and less airway constriction. They also found that the immune systems of the mice on the high-fibre diet were less able to turn on so-called 'effector cells,' which play a key role in asthma.
Finally, the investigators found that the mice given propionate produced more 'precursor cells' that develop into 'dendritic cells' in the immune system, that protect against asthma.
"Addressing [these findings] in rigorous clinical studies is important though before we draw strong conclusions, which is something we hope to do in the future," said Marsland. "Diet certainly not only influences our intestinal tract (and associated diseases), but it can have much broader implications for other tissues and diseases. Thus, one of the simplest things that we can do to be healthy overall is to eat well!"