Fiber has been receiving a lot of press lately and rightly so – it is an extremely important nutrient that most of us don’t get enough of.

So what exactly does fiber do in your body?

First, it might be helpful to understand what your colon does. Your colon’s main job is to complete the digestion process by removing excess water from food wastes that enter from the small intestine. If not enough water is absorbed, waste passes too quickly resulting in diarrhea-like symptoms. This also means that too much water being absorbed will lead to constipation.
Whereas protein, fats, and carbohydrates are almost entirely absorbed in the small intestines, fiber passes through the large intestine virtually unchanged. It does not provide your body with any energy or nutrients but is still critically important. Fiber basically helps keep food moving through the intestine and helps to expand the inside walls of the colon to ease the passage of waste. It does this by slowing the absorption of nutrients, absorbing water, and binding cholesterol. When you consume enough fiber, your body can absorb water which makes your stool larger and softer; this stimulates the intestinal muscles so less pressure is needed to expel the waste.

Fiber comes in two forms – Soluble and Insoluble

Soluble fiber is "soluble" in water. When mixed with water it forms a gel-like substance and swells.  It is readily fermented in the colon into gases and physiologically active byproducts. Soluble fiber has many benefits, including moderating blood glucose levels and lowering cholesterol. The scientific names for soluble fibers include pectins, gums, mucilages, and some hemicelluloses. Good sources of soluble fiber include oats and oatmeal, legumes (peas, beans, lentils), barley, fruits and vegetables (especially oranges, apples and carrots).

Insoluble fiber does not absorb or dissolve in water. It passes through our digestive system in close to its original form. Insoluble fiber offers many benefits to intestinal health, including a reduction in the risk and occurrence of colorectal cancer, hemorrhoids, and constipation. The scientific names for insoluble fibers include cellulose, lignins, and also some other hemicelluloses. Most of insoluble fibers come from the bran layers of cereal grains.
Both forms of fiber add bulk to your diet, which makes you feel full faster, in turn reducing the chance of overeating. Fiber does not bind to vitamins and minerals and therefore does not restrict their absorption. In fact, evidence exists that fermentable fiber sources actually improve absorption of minerals, especially calcium.

Fiber may help calm the immune system

Insoluble dietary fibre, or roughage, not only keeps you regular, say Australian scientists; it also plays a vital role in 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 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.
Published 29 October in Nature, 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.
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.

There is plenty of evidence to suggest that bacteria and their by-products play an important role in people. An American study published in Nature in 2006 compared the bacteria in the guts of obese and lean people. The obese people were put on a diet, and as they lost weight their bacteria profile gradually came to match that of the lean people.

Another study looked at what diets might do to short chain fatty acid levels. Obese people were put on three different diets over time – high, medium and low fibre – and there was a direct correlation between the level of carbohydrate, or fibre, in the diet and the level of short chain fatty acids.

The conclusions drawn from the current research provide some of the most compelling reasons yet for eating considerably more unprocessed whole foods - fruits, vegetables, grains, nuts and seeds.

Dietary fibre, of course, has many known health benefits in addition to those discussed above, including reduced risk of cardiovascular disease and certain cancers, and various health organizations around the world recommend daily minimum levels. It is certain that the majority of people in countries like Australia, the United States and Britain eat much less fibre than they need to stay healthy.

“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.

Eat more fiber!

What all this tells us is that basically we need to eat more fiber! Carbohydrates seem to be the current enemy in the average person’s media-guided approach to diet these days, and unfortunately they are the greatest provider of this very important nutrient. And as we also seem to be farming all the nutrients out of the soil we grow our fruit and veges in, we should be trying to add more of these great foods to our daily intake as well. So stop being scared of carbs, pump up the fruit and veges, and live a longer, healthier life!