Irritable Bowel Syndrome Message Boards | Re: Types of dietary fiber

The categorization of fibers is a bit more complicated. Here are a some quotes from the reference below you might find useful. It seems to clear up some of the confusion about the solubility of RS. It also contains some tables you may find useful. The Linus Pauling Institute web site at Oregon State U on the fiber page says "Beta-glucans, gums, mucilages (e.g., psyllium), pectins, and some hemicelluloses are soluble fibers while cellulose, lignin, some pectins, and some hemicelluloses are insoluble fibers (10)." It seems not all hemicelluloses are insoluble.

"Insoluble fibre has passive water-attracting properties that help increase bulk, soften stools and shorten transit time through the intestinal tract. Most insoluble fibres are also resistant to fermentation in the large bowel. Soluble indicates a fibre source that readily holds water, forming a viscous solution as it passes through the gastrointestinal tract, and is fermented"

"First, there are many components, such as the resistant starches and the oligosaccharides, which, by their indigestible nature, could be considered to contribute to the total amount of dietary fibre in the diet. If such components were included in a definition of dietary fibre, they do not fit into this neat soluble/insoluble categorisation."

"Resistant starches and oligosaccharides have physiological characteristics that are more akin to other similar components than to 'soluble' or 'insoluble' components. As a result, were these compounds included, they would need to be considered separately."

"Second, to differentiate by solubility in water ignores the 'metabolism' that occurs in the large bowel. Here, fermentation of different types of fibre produces endproducts with significant health effects, although ffects are not predicted by solubility. It is now clear that some insoluble fibres are in fact fermented in the large bowel whereas some soluble fibres have no clear health effect."

"Defining dietary fibre physiologically allows recognition of the analogous carbohydrates. These are carbohydrates with structures and physiological properties similar to those of naturally occurring dietary fibres."

"In summary, a workable definition of dietary fibre should: clarify the constituent makeup of dietary fibre; recognise that a primary characteristic is resistance to digestion and absorption in the small intestine and fermentation in the large intestine; and demonstrate that fibre has physiological properties."

Reference
Lunn, J. & Buttriss, J. L. Carbohydrates and dietary fibre . Nutrition Bulletin 32, 21-64 (2007).

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