Sydney, Oct 30 (IANS) Insoluble dietary fibre or roughage plays a vital role in the immune system, keeping certain diseases at bay, according to researchers.

The indigestible part of all plant-based foods pushes its way through most of the digestive tract unchanged, acting as a kind of internal broom. When it arrives in the colon, bacteria convert it to energy and compounds known as 'short chain fatty acids'.

These are already known to alleviate the symptoms of colitis, an inflammatory gut condition.

Similarly, probiotics and prebiotics, food supplements that affect the balance of gut bacteria, reduce the symptoms of asthma and rheumatoid arthritis, also inflammatory diseases. Until now no-one has understood why.

Breakthrough research by a Sydney-based team makes new sense of such known facts by describing a mechanism that links diet, gut bacteria and the immune system, the website Science Alert reported.

PhD student Kendle Maslowski and professor Charles Mackay from the Garvan Institute of Medical Research, in collaboration with the Co-operative Research Centre for Asthma and Airways, have demonstrated that GPR43, a molecule expressed by immune cells and previously shown to bind short chain fatty acids, functions as an anti-inflammatory receptor.

'The notion that diet might have profound effects on immune responses or inflammatory diseases has never been taken that seriously,' said Professor Mackay. 'We believe that changes in diet, associated with western lifestyles, contribute to the increasing incidences of asthma, Type 1 diabetes and other autoimmune diseases. Now we have a new molecular mechanism that might explain how diet is affecting our immune systems.'

'We're also now beginning to understand that from the moment you're born, it's incredibly important to be colonised by the right kinds of gut bacteria,' added Kendle.

'The kinds of foods you eat directly determine the levels of certain bacteria in your gut.'

'Changing diets are changing the kinds of gut bacteria we have, as well as their by-products, particularly short chain fatty acids. If we have low amounts of dietary fibre, then we're going to have low levels of short chain fatty acids, which we have demonstrated are very important in the immune systems of mice.'

Mice that lack the GPR43 gene have increased inflammation, and poor ability to resolve inflammation, because their immune cells can't bind to short chain fatty acids.

'The role of nutrition and gut intestinal bacteria in immune responses is an exciting new topic in immunology, and recent findings including our own open up new possibilities to explore causes as well as new treatments for inflammatory diseases such as asthma,' said Mackay.

The results were published Oct 29 in the journal Nature.