Winter 2001 Issue — Inulin, a pure soluble dietary fibre

Diederick Meyer

Sensus Operations CV, The Netherlands

Bryan Tungland

Imperial Sensus, Sugarland, Texas, United States

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People have been consuming dietary fibres for years even if dietary fibre was not defined as such. Everybody can take advantage of their health benefits since dietary fibres can be found in our everyday diet. Indeed, we can find fibres in vegetables, fruits, whole grains and nuts. Despite the health benefits that dietary fibres have on reducing the risk of chronic disease, the intake remains.

Low in many populations worldwide, the fibre intake recommendations (table 1) are not followed by the consumers. We associate the fibre intake with the increase of stool bulk and the improvement of laxation, mineral absorption. Recent epidemiological data show that a diet high in fibre generally reflects healthier life style and fibre intake can be viewed as a maker of healthy diet.

Table 1

Since the beginning of the year, inulin is recognised officially as a dietary fibre in United Kingdom. The Food Standard Agency adopted a Guidance note. The Guidance Note recommends that the reference procedure for analysis of dietary fibre is the AOAC international method 997.08 an analysis specific for fructans, such as inulin, in food products. This method is recommended to the manufacturers to ensure consistent labelling of inulin as a dietary fibre.

Characteristics of inulin

Inulin is a naturally occurring storage carbohydrate, present in numerous plants. It is built up of 2-60 fructose units with one terminal glucose molecule. The low molecular weight fractions of inulin (DP 3-20) are also known as oligofructose. Inulin can scarcely be hydrolysed by gastric acid; digestion by human digestive enzymes does not occur, nor absorb intact inulin. The total amount of consumed inulin reaches the colon intact where it is fermented by endogenous bacteria. These characteristics, (non digestible carbohydrate from plant that reaches the colon largely intact and evokes physiological functions) qualify inulin as dietary fibre. Inulin further falls under the sub-category of highly fermentable non-viscous soluble fibres.

Physiological effects and the mechanisms of action

The best generally known effects of dietary fibre is its influence on stool. It decreases the time for food-passage through entire gastro-intestinal tract and increases faecal bulk. For these effects different forms of dietary fibre are being used quite successfully in case of constipation. Specific effects of soluble dietary fibre can be related to its actual place in the body. In the stomach soluble dietary fibre may increase the viscosity of the contents, thereby slowing down the rate at which food components empty from the stomach into the small intestine. This might result in a decreased feeling of hunger and reduction of food intake. In the small intestine soluble dietary fibre create a viscous environment, which inhibits absorption of nutrients. The major effect in the upper gastro-intestinal tract is an improved glucose-tolerance. Inulin reaches the large intestine intact. There it subsequently will be hydrolysed and fermented by specific caecal and colonic bacteria. Much research in this area has been done, from which can be concluded that in particular the growth of the beneficial genera of Bifidobacteria is increased; moreover inulin negatively influences the growth of pathogenic strains such as Clostridium perfringers; therefore inulin can be classified as a bifidogenic factor.

Through the caeco-colonic fermentation, inulin is converted into large amounts of Short Chain Fatty Acids (SCFA). The specific micro-flora also produces lactic acid, which together with SCFA leads to a decrease in colonic pH. In this way inulin creates circumstances that may be antagonistic to the growth of pathogens and putrefactive bacteria. Increased amount of SCFA also seem to mediate a local growth of the intestinal epithelium, partly as a direct source of energy, partly via a stimulation of certain growth hormones. The resulting increased thickness of the intestinal wall reduces the risk of bacterial translocation. Part of the produced SCFA (mainly acetate and propionate) will be absorbed into the bloodstream. They can either be used as a fuel or give rise to specific effects: propionate suppresses cholesterol synthesis and acetate might positively influence the postprandial glucose-response.

Applications

Frutafit® - inulin commercialised by SENSUS in the Netherlands is an excellent source of soluble dietary fibre and can be used in the general healthy diet to increase fibre-intake toward publicly recommended levels. Because of its diversity of effects, Frutafit® - inulin might be useful for specific purposes.

Frutafit® - inulin in dietary treatment of constipation

Frutafit® - inulin is a welcome supplementary source of dietary fibre to be used in fibre-rich diets. Frutafit® - inulin is a purified fibre and is easy to supplement to foods without significantly influencing taste or visual appearance. Furthermore, Frutafit® - inulin is very stable to heat and thus can be easily processed into a bread, cookies, pasties or ice cream.

A recent study involving 35 elderly constipated persons showed that daily dietary supplements of inulin improved stool frequency tremendously (Fig 2). Stools were soft, but diarrhoea was not observed. Furthermore, all patients reported the absence of nausea and headaches, complaints that often accompany constipation.

Another group of investigators reported results of a study with inulin in 9 healthy young men. They revealed that the increase in daily stool output, caused by a dietary supplementation of 22 gram inulin, could be associated to a significant increase in faecal bacterial weight and to significant increase in water content (Fig 3).

The positive effects on constipation of daily intake of inulin, categorised as soluble fermentable dietary fibre, can be associated to increased microbial, water content of the stool, and increased stool weight. The consistency of the stools get softer, because of the larger content of water. Also increased bowel frequency may be noted. These physiological effects together with its excellent physical properties for a broad spectrum of applications make Frutafit® - Inulin a highly recommendable ingredient in products to resolve constipation. For adults we recommend a daily intake of 10-20 grams inulin spread over the day. At this dosage no adverse effects, such as excessive flatulence or other intestinal discomfort, will be experienced. Potential applications are: fibre-enriched health drinks, bread or dairy products, enteral formulations and dietary supplements. Combinations with other fibre sources can increase the benefits of Frutafit® - Inulin in these applications.

Frutafit® - Inulin boosts mineral absorption

It is well recognised that dietary fibre binds metal ions. Though the increase of fibre intake is one of the most wide-spread dietary fibre recommendations to the western public, there is also concern that such increase could lead to reduced intestinal absorption of certain minerals.

You can enjoy a high fibre intake without worrying about mineral deficiency. Inulin provides the solution. Inulin is characterised by its well-documented physiological effects as a (soluble) dietary fibre. Yet, inulin intake does not inhibit mineral absorption. On the contrary, physiological research shows that regular consumption of inulin significantly enhances the absorption of minerals, e.g. Cations such as:

• Ca²+,
• Mg²+,
• Zn²+,
• Cu²+,
• Fe²+.

Mechanisms of action

It has been shown that inulin intake exerts its actions on mineral absorption following fermentation in the colon. In your colon, dietary inulin is totally fermented by the natural microflora to yield short chain fatty acids and lactic acid. Any inulin mineral complexes are degraded during fermentation, liberating the minerals and thus making them available for bio-absorption.

In addition, the acids produced by fermentation lower the pH of the colon lumen by 1-2 units. The solubility/bioavailability of many mineral salts, e.g. Ca-phosphate, is markedly enhanced in this dilute acidic environment.

Moreover, research also suggests that SCFA, especially butyrate, seem to stimulate proliferation of colon epithelial cells, thereby increasing the absorptive capacity of the epithelium. Other mechanisms may also play a role, such as the increase of calcium binding proteins in certain segments of the colon.

The increase of fibre consumption in the diet is directly dependant on the foods that possess quality taste properties and have a content in fibres. It is important from a food product development that the food product should have more than fibre content, it should also provide enhanced functional products to make a better taste, hence offering a high fibre intake. With these considerations in mind and reinforced by better consumer awareness and supported by new food regulations, new health enhancing food ingredients are providing a means to develop a market with healthy products with wide international interest.

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