Fiber Helps Immune System Function

(October 29, 2009) - Load up on those fruits and vegetables. There is more evidence that they help keep you healthy. Insoluble dietary fiber (Read about "Fiber & Health"), or roughage, not only keeps you regular, say scientists, it also may play a vital role in the immune system (Read about "The Immune System"), keeping certain diseases at bay.

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 help alleviate the symptoms of colitis (Read about "Ulcerative Colitis"), say the study authors.

Similarly, probiotics and prebiotics, food supplements that affect the balance of gut bacteria, are believed to reduce the symptoms of asthma and rheumatoid arthritis (Read about "Asthma" "Rheumatoid Arthritis"), also inflammatory diseases. Until now, no one has understood why.

Published in Nature, the research makes new sense of this connection by describing a mechanism that links diet, gut bacteria and the immune system. The research claims 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 Charles Mackay, one of the researchers. "We believe that changes in diet, associated with western lifestyles, contribute to the increasing incidences of asthma, Type 1 diabetes (Read about "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 colonized by the right kinds of gut bacteria," added Kendle Maslowski, another of the researchers. "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 fiber, 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."

"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.