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Inulins are a group of naturally occurring oligosaccharides (several simple sugars linked together) produced by many types of plants. They belong to a class of carbohydrates known as fructans. Inulin is used by some plants as a means of storing energy and is typically found in roots or rhizomes. Most plants which synthesize and store inulin do not store other materials such as starch.
Inulin is used increasingly in foods, because it has excellent nutritional and functional characteristics. It ranges from completely bland to subtly sweet and can be used to replace sugar, fat, and flour. This is particularly advantageous because inulin contains one-third to one-fourth the food energy of sugar or other carbohydrates and one-sixth to one-ninth the food energy of fat. It also increases calcium absorption (PMID 16087995) and possibly magnesium absorption (PMID 12514257), while promoting probiotic bacteria. Nutritionally, it is considered a form of soluble fiber, and it is important to note that consuming large quantities (particularly for sensitive and/or unaccustomed individuals) can lead to gas and bloating. Inulin has a minimal impact on blood sugar, making it generally considered suitable for diabetics and potentially helpful in managing blood sugar-related illnesses.
Biochemistry
Inulins are polymers 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, which has 2 fructose units and 1 glucose unit.
Inulins with a terminal glucose are known as alpha-D-glucopyranosyl-abbreviated as GpyFn. Inulins without glucose are beta-D-fructopyranosyl-[D-fructofuranosyl(n-1)-D-fructofuranosides, abbreviated as FpyFn where n is the number of fructose residues and py is the abbreviation for pyranosyl.
Hydrolysis of inulins may yield oligofructose, which are polymers with a degree of polymerization (DP) of <= 10.
Uses and health benefits
Inulin is indigestible by the 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 metabolise inulin, with the release of significant quantities of carbon dioxide and/or methane. Inulin-containing foods can be rather gassy, particularly for those unaccustomed to inulin, and these foods should be consumed in moderation at first. However, given some time, most people can adapt to consuming fairly high levels of inulin without side effects.
Inulin is not broken down into simple sugars (monosaccharides) by normal digestion, so it does not elevate blood sugar levels, hence, helping diabetics regulate blood sugar levels.
Inulin is also a highly effective prebiotic, stimulating the growth of beneficial probiotic bacteria in the gut. As mentioned, inulin passes through the stomach and duodenum undigested and is highly available to the gut bacterial flora. This contrasts with proprietary probiotic formulations based on yogurt or milk in which the bacteria have to survive very challenging conditions through the gastrointestinal tract before they are able to colonize the gut.
Some traditional diets contain up to 20g per day of inulin or oligofructose. Many foods naturally high in inulin or oligofructose, such as chicory, garlic and leek, have been seen as "stimulants of good health" for centuries (PMID 10395609).
Inulin can be found in commerically available products such as Fibersure from the Makers of Metamucil. Fibersure is a fiber supplement powder that can be added to foods or beverages without changing the taste or texture. It performs well in cooking and baking applications and can be an easy way to add additional fiber to the diet through foods and drinks.
Health risks
The New England Journal of Medicine has reported on allergic reactions to inulin in foods This article documents the case of one adult male with a severe allergy to inulin [http://allergies.about.com/cs/inulin/a/aa051500a.htm.
Natural sources of inulin
Plants that contain high concentrations of inulin include:
- Dandelion (Taraxacum officinale)
- Wild Yam (Dioscorea sp.)
- Jerusalem artichokes (Helianthus tuberosus)
- Chicory (Cichorium intybus)
- Jicama (Pachyrhizus erosus)
- Burdock (Arctium lappa)
- Onion (Allium cepa)
Other useful information
Inulin, as it is completely filtered at the glomerulus and is neither secreted nor reabsorbed in the tubules, has been used as an important medical test of renal function, specifically a measure of glomerular filtration rate. The measurement of GFR by inulin is still considered the gold-standard, although it has been now largely replaced by other, simpler measures which are actually estimations of GFR, which have been confirmed in large cohorts of patients with chronic kidney disease (e.g. Iothalomate, EDTA, creatinine clearance).
External links
- Cargill's Inulin Homepage
- Orafti, a Major Inulin Manufacturer
- PMID 15877886 - Introducing inulin-type fructans.
"Inulin"