Inulin

From Wikipedia, the free encyclopedia

Inulin

Molecular formula	C_6nH_10n+2O_5n+1
Molar mass	Polymer; depends on n
CAS number	[9005-80-5]
PubChem	24763
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Not to be confused with insulin.

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 unusual nutritional 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^[1] and possibly magnesium absorption^[2], while promoting intestinal 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.

1 Biochemistry
2 Calculation of Glomerular Filtration Rate (GFR)
3 Uses and health benefits
4 Health risks
5 Natural sources of inulin
6 References
7 External links

[edit] 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-ketose, which has 2 fructose units and 1 glucose unit.

Inulins with a terminal glucose are known as alpha-D-glucopyranosyl-[beta-D-fructofuranosyl](n-1)-D-fructofuranosides, 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.

[edit] Calculation of Glomerular Filtration Rate (GFR)

Inulin is uniquely treated by nephrons in that it is completely filtered at the glomerulus but neither secreted nor reabsorbed by the tubules. This property of inulin allows the Clearance (medicine) of inulin to be used clinically as a highly accurate measure of Glomerular filtration rate (GFR)—the percentage of plasma from the afferent arteriole that is filtered into Bowman's capsule.

It is useful to contrast the properties of inulin with those of para-aminohippuric acid (PAH). PAH is completely filtered from plasma at the glomerulus and not reabsorbed by the tubules, in a manner identical to inulin. PAH is different from inulin in that the fraction of PAH that bypasses the glomerulus and enters the nephron's tubular cells (via the Peritubular capillaries) is completely secreted. Renal Clearance (medicine) of PAH is thus useful in calculation of renal plasma flow (RPF), which empirically is (1-Hematocrit) times renal blood flow. Of note, the clearance of PAH is reflective only of RPF to portions of the kidney that deal with urine formation, and thus underestimates actualy RPF by about 10%. ^[3]

The measurement of GFR by inulin is still considered the gold-standard. Practically, however, it has now been largely replaced by other, simpler measures that are approximations of GFR. These measures, which involve clearance of such substrates as EDTA and creatinine, have had their utility confirmed in large cohorts of patients with chronic kidney disease.

[edit] Uses and health benefits

Inulin is indigestible by the human enzymes ptyalin and amylase, which are adapted 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. Most individuals can adapt to increased dietary fiber and most Americans consume only half the daily recommended value of dietary fiber.

There are two types of dietary fiber, soluble and insoluble. Insoluble fiber increases the movement of materials through the digestive system and increases stool bulk; it is especially helpful for those suffering from constipation or stool irregularity. Soluble fiber dissolves in water to form a gelatinous material. It can help lower blood cholesterol and glucose levels. Inulin is considered a soluble fiber.

Because normal digestion does not break inulin down into monosaccharides, it does not elevate blood sugar levels and may therefore be helpful in the management of diabetes. Inulin is also an effective prebiotic, stimulating the growth of beneficial bacteria in the gut. 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 Lactic acid bacteria (LAB) 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.^[4]

The (American) National Academy of Sciences' Institute of Medicine's daily dietary fiber recommendations for adults range from 21 grams for women over 51 years of age to 38 grams for men under 51 years of age. In order to reach the recommended daily amount for that latter category, a man would have to consume 19 FiberChoice tablets.

Inulin is also used in medical tests to measure the total amount of extracellular volume and determine the function of the kidneys.^[5]

[edit] Health risks

Allergic reactions to inulin in foods were reported in the New England Journal of Medicine.^[6] This article documents the case of one adult male with a severe allergy to inulin.^[7]

[edit] Natural sources of inulin

Plants that contain high concentrations of inulin include:

Dandelion (Taraxacum officinale)
Wild Yam (Dioscorea spp.)
Jerusalem artichokes (Helianthus tuberosus)
Chicory (Cichorium intybus)
Jicama (Pachyrhizus erosus)
Burdock (Arctium lappa)
Onion (Allium cepa)
Garlic (Allium sativum)
Agave (Agave spp.)

[edit] References

^ Abrams S, Griffin I, Hawthorne K, Liang L, Gunn S, Darlington G, Ellis K (2005). "A combination of prebiotic short- and long-chain inulin-type fructans enhances calcium absorption and bone mineralization in young adolescents.". Am J Clin Nutr 82 (2): 471-6. PMID 16087995.
^ Coudray C, Demigné C, Rayssiguier Y (2003). "Effects of dietary fibers on magnesium absorption in animals and humans.". J Nutr 133 (1): 1-4. PMID 12514257.
^ Costanzo, Linda. Physiology, 4th Edition. Philadelphia: Lippincott Williams and Wilkins, 2007. Page 156-160.
^ Coussement P (1999). "Inulin and oligofructose: safe intakes and legal status.". J Nutr 129 (7 Suppl): 1412S-7S. PMID 10395609. Text)
^ MedlinePlus DrugInfo uspdi-202300
^ Fabienne Gay-Crosier, M.D. et al., Anaphylaxis from Inulin in Vegetables and Processed Food (Correspondence), New England Journal of Medicine, 342(18), 1372. May 4, 2000.
^ http://allergies.about.com/cs/inulin/a/aa051500a.htm