Probiotics The Effects of Inulin on Gut Health and Bifidobacterial Populations in the Colon George C Fahey, Jr, PhD Department of Animal Sciences, University of Illinois


Abstract


Inulins are important constituents of dietary fiber that are present in a wide variety of foodstuffs of plant origin that act as prebiotics, which enhance gut colonization by beneficial bacteria, principally the bifidobacteria. Inulins consist of linear and branched polymers of repeating fructosyl units that range between 2 and 60 units in length. These polysaccharides are resistant to the host metabolism in the upper digestive tract, but are fermented by bacteria in the colon. Diets in the developed world that often comprise highly processed foods contain lower than desirable levels of inulin and dietary fiber generally. Inulins added to foods help maintain the mucosal barrier in the gut and are claimed to reduce the risk of cardiovascular disease and cancer and maintain gut health particularly in infants and the elderly. In recent years, inulins have been increasingly recognized as important in digestive health and are added to a variety of food products to take advantage of their prebiotic effects. This trend is likely to continue.


Keywords Inulins, fructans, prebiotic, dietary fiber, bifidobacteria, gut microflora, health benefits


Disclosure: The author has no conflicts of interest to declare. Acknowledgment: Editorial assistance was provided by Touch Briefings. Received: September 30, 2010 Accepted: November 5, 2010 Citation: US Gastroenterology & Hepatology Review, 2010;6:58–63 Correspondence: George C Fahey, Jr, PhD, Department of Animal Sciences, University of Illinois, 132 Animal Sciences Laboratory, 1207 West Gregory Drive, Urbana, IL 61801. E: gcfahey@illinois.edu


Support: The publication of this article was funded by General Mills. The views and opinions expressed are those of the author and not necessarily those of General Mills.


Inulin and other non-digestible oligosaccharides (NDOs) continue to attract increasing attention as prebiotics, which are defined as “a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-being and health.”1


Data on the mechanisms and


benefits of prebiotics such as inulin are accumulating in parallel with an understanding of the complex interactions among beneficial micro-organisms, notably the bifidobacteria, and other gut microflora, host tissues, and metabolism. The availability of marketed prebiotics and probiotics (selected strains of live bacteria) and their consumption in many populations worldwide is increasing, making this subject increasingly important for the physician.


Inulin is an important constituent of dietary fiber. Dietary fibers are a diverse collection of different edible carbohydrates predominantly of plant origin, which, in addition to inulin, include non-starch polysaccharides such as cellulose and also dextrins, lignins, waxes, chitins, pectins, and oligosaccharides.2–5


The consumption of adequate dietary fiber is


widely accepted as critical in maintaining digestive and general health. Traditionally, dietary fiber has been divided into two types: soluble and insoluble.6


The soluble types include inulin and are fermentable in the 58


gut, they are derived from many sources, and are claimed to lower cholesterol levels and reduce the risk of heart disease. The insoluble types of fiber are less readily fermentable—they are primarily cellulose and hemicellulose—and are considered more important in increasing fecal mass, gut transit times, and laxation. More recently, the US Institute of Medicine has changed this definition describing total fiber as consisting of: dietary fiber, the non-digestible carbohydrates as they naturally exist in plants, and functional fiber, which is defined as refined or synthetic fiber with demonstrated health benefits.7


The property of some dietary fibers,


particularly inulin, to promote gut colonization by beneficial bacterial populations and inhibit pathogenic types is significant in clinical medicine, food manufacture, and the composition of healthy diets.


This article discusses the mechanisms that underlie the prebiotic activity of inulin and considers our understanding of how its role in gut microbiology translates into both established and potential health benefits.


Defining Inulin-type Prebiotics


Inulin is a generic term that covers all linear fructans with beta (2 → 1) fructosyl-fructose glycosidic bonds, with a degree of polymerisation ([DP] number of repeat units in an oligomer or polymer chain) generally ranging


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