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Dietary Fiber Helps Immune Response

October 29, 2009

Australian researchers say they may have found yet another reason why we ought to be packing our diets full of fresh fruits and vegetables.  According to a new study released by Sydney’s Garvan Institute of Medical Research, dietary fiber isn’t just important for keeping your grandmother regular, but may in fact play a significant role in staving off chronic illnesses like arthritis, diabetes and asthma.

Researchers have for some time known that fiber-rich foods such as legumes, whole grain breads and fresh fruits and vegetables are processed by intestinal bacteria to produce byproducts known as short chain fatty acids “” biomolecules that naturally treat various inflammatory diseases of the bowels.

According to Professor Charles Mackay of the Garvan Institute, his group “” which collaborated with research labs in the U.S. and Brazil “” was able to more closely elucidate the nature of the effects of fiber on intestinal disorders, which they believe may have much broader implications for our understanding of the relationship between diet and immune response.

In short, Professor Mackay and PhD student Kendle Maslowski were able to show that a molecule known as GPR43 “” known to be present in immune cells and used to bind short chain fatty acids “” also doubles as an anti-inflammatory receptor.

“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 Mackay told AFP.

The team’s work, published in the current edition of Nature, points to a potential link between diet and immune responses that has hitherto been the subject of guesswork.

“The notion that diet might have profound effects on immune responses or inflammatory diseases has never been taken that seriously,” explained 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.”

According to Maslowski, taking care of the friendly bacteria that make their homes in our gut may be much more important to lifelong health than people realize.

“We’re [...] beginning to understand that from the moment you’re born, it’s incredibly important to be colonized by the right kinds of gut bacteria,” she explained.

“The kinds of foods you eat directly determine the levels of certain bacteria in your gut [and] 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.”

In lab studies, the team demonstrated that mice lacking the gene for GPR43 experienced a significantly increased incidence of intestinal inflammation and a diminished ability to fight off existing inflammation, presumably because their immune cells were unable to bind to short chain fatty acids.

The group’s work is corroborated by a 2006 study published in Nature that compared bacteria colonies in the intestines of obese people with those found in leaner subjects.  The obese people were then put on a diet, and scientists observed that as they began to shed pounds the constitution of their bacteria colonies progressively came to look more and more like that seen in the leaner people.

Mackay expressed enthusiasm over the potential that his team’s researcher could help to shed light on this little-understood branch of immunology.

“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 Professor Mackay.

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