An apple a day may keep the doctor away but a fibre-filled diet could also hold the key to keeping asthma, diabetes and arthritis at bay, according to Australian research released Thursday.

Scientists at Sydney's Garvan Institute of Medical Research say that fiber not only helps keep people regular, it boosts the immune system so it can better combat inflammatory diseases.

When foods high in fiber, such as dried fruit and beans, reach the gut, bacteria convert them to compounds known as short chain fatty acids. These acids are known to alleviate some inflammatory disease in the bowel.

Researcher Charles Mackay said that the team, which worked with scientists in Australia, the US and Brazil, was able to draw a clearer picture of this relationship, work which has implications for other diseases.

They demonstrated that a molecule used by immune cells and previously shown to bind short chain fatty acids also functioned as an anti-inflammatory.

"The important point about our work is that we provide the molecular explanation that links fiber in the diet to the micro-organisms in our gut to the affect on the immune response," Professor Charles Mackay told AFP.

The research, published in the latest edition of Nature, indicated that diet may have profound effects on immune responses or inflammatory diseases, he said.

"We believe that changes in diet, associated with western lifestyles, contribute to the increasing incidences of asthma, Type 1 diabetes and other auto-immune diseases," he said.

"Now we have a new molecular mechanism that might explain how diet is affecting our immune systems."

Copyright AFP