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Inulins are naturally occurring oligosaccharides (several simple sugars linked together) produced by many types of plants. They belong to a class of carbohydrates known as fructans. Inulins are mainly comprised of fructose units and typically have a terminal glucose. The fructose units in inulins are joined by a beta-(2-1) glycosidic link. Plant inulins generally contain between 2 to 140 fructose units. The simplest type of inulin is 1-kestose is which has two fructose units and one of glucose.
Inulins with a terminal glucose are known as alpha-D-glucopyranosyl-[beta-D-fructofuranosyl](n-1)-D-fructofuranosides, abbreviated to GpyFn. Inulins without glucose are beta-D-fructopyranosyl-[D-fructofuranosyl](n-1)-D-fructofuranosides, abbreviated to FpyFn where n is the number of fructose residues and py is the abbreviation for pyranosyl.
Inulin is used by plants as a means of storing energy and is typically found in roots or ryhzomes. Most plants which synthesise and store inulin do not store other materials such as starch.
People have used plants containing inulin to help relieve diabetes mellitus which is a condition of unbalanced insulin levels resulting in unhealthy blood sugar levels. Inulin is incapable of digestion by human enzymes ptyalin and amylase, which are designed to digest starch. As a result, Inulin passes through much of the digestive system intact. It is only in the colon that bacteria use Inulin as an energy source, with the release of significant quantities of carbon dioxide and/or methane. Inulin containg foods are therefore notoriously gassy and not recommended for the socially sensitive.
Because Inulin is not broken down into simple sugars (monosaccharides) by normal digestion it does not contribute to blood sugar levels and thus enables sufferers from Diabetes to manage their condition more reliably. Inulin is however wholly unrelated chemically to Insulin; the similarities in name does not relate to any similarity in form or function.
Inulin is also a highly effective prebiotic, stimulating the growth of beneficial probiotic bacteria in the gut. Because Inulin passes through the stomach and duodenum undigested, it is highly available to the gut baterial flora. This contrasts with prorietary probiotic formulations such as yogurt and milk in which the bacteria have to survive the very challenging conditions in the stomach before they are able to recolonize the gut
Some plants which contain high concentrations include Dandelion (Taraxacum officinale), Wild Yam (Dioscorea sp.), and Jerusalem artichokes (Helianthus tuberosus).
Inulin, because it is neither secreted nor reabsorbed in the kidney, was used in a historically important medical test of renal function, specifically a measure of glomerular filtration rate, now largely measured by the creatinine clearance test. The inulin clearance test was performed by injecting inulin, waiting for it to be distributed, and then measuring plasma and urine inulin concentrations.
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